BULLETIN 423 PLATE I

AND DUST GALLERY NO. 1, PITTSBURG TESTING STATION.
DEPARTMENT OF THE INTERIOR

UNITED STATES GEOLOGICAL SURVEY

GEORGE OTIS SMITH, DIRECTOR

,ErrrN 423

A PRIMER ON EXPLOSIVES 

FOR COAL MINERS

BY

CHARLES E. MUNROE

AND

CLARENCE HALL

WASHINGTON

GOVERNMENT PRINTING OFFICE

1909

CONTENTS.

Page.

Introduction............................................................. 9

Combustion and explosion................................................ 11

Fire................................................................. 11

Combustible substances............................................... 11

Explosion ........................................................... 11

Dust explosions ....................................................^. 11

Air necessary to ordinary combustion.................................. 12

Oxygen of the air necessary for combustion............................ 12

Oxygen from saltpeter................................................ 12

Saltpeter supports combustion......................................... 12

Charcoal with saltpeter produces heat and gas.......................... 12

Sulphur is added to make the mixture ignite easily..................... 13

Chile saltpeter contains oxygen ..........................___:........... 13

Oxygen in other bodies............................................... 13

Nitric acid from saltpeter............................... .............. . 13

Putting oxygen into cotton, glycerin, etc............................... 14

Sensitiveness and violence of fulminate of mercury..................... 14

Low explosives ....................................................... 14

High explosives...................................................... 14

Confinement essential to use of explosives............................. 15

Folly of attempting to make explosives ................................ 15

Explosives................................................................ 15

Gunpowder.......................................................... 15

Black blasting powder................................................ 15

Danger from dampness ............... ................................ 16

Keep powder dry .................................................... 16

Granulating powder.................................................. 16

Size of powder grains................................................. 16

Danger in using a mixture of different-sized grains...................... 17

Potassium chlorate................................................... 17

Nitrocellulose........................................................ 18

Nitroglycerin ......................................................... 18

Nitroglycerin freezes .................................................. 19

Liquid nitroglycerin is especially dangerous............................ 19

Dynamite............................................................ 19

Explosive gelatin and gelatin dynamite................................ 20

All explosives containing nitroglycerin freeze........................... 20

Dynamite cartridges.................................................. 20

Packing dynamite.......... i ......................................... 20

Nitrostarch ...................;...................................... 20

Ammonium nitrate................................................... 21

Nitro-substitutioii compounds......................................... 21

Why nitro-substitution compounds are so called......................... 21

Fulminates .^........................................................ 22

Danger with fulminates............................................... 22

Warning against manufacturing explosives ............................. 22

3
4 CONTENTS.

Page.

Explosives for use in coal mines...---.-.....................__.....__...... 22

Number of explosives. ........_...................._.........._........ 22

Explosives in open work.. ........................._...___.____..__.__. 23

Explosives in inclosed work........................_..................' 23

Danger from flames in coal mines...................................... 23

Noxious gases ............ r ........................................... 23

Investigation by Geological Survey.................................... 23

Testing station at Pittsburg ........................................... 24

Explosives gallery No. 1.............................................. 24

Permissible explosives........-......-.---------...................... 24

Classification of permissible explosives................................. 25

Advantages of permissible explosives ................................... 25

Danger from permissible explosives.................................... 25

Freezing of permissible explosives..................................... 26

Danger from exposure to high temperatures............................ 26

Do not expose to sunlight.................................. '. .......... 26

Keep explosives dry.................................................. 26

Do not dry explosives too much ............................'...........' 26

Use explosives promptly.............................................. 26

Injury to cartridges from rough handling .............................. 27

Care in handling cartridges............................................. 27

. Shipment of explosives ............................................... 27

Storage of explosives ................................................. 27

Magazines ........................................................... 27

Detonators never to be stored with other explosives .................... 27

Opening boxes of explosives ................:......................... 28

Thawing frozen explosives............................................ 28

Thawers for explosives ............................................... 28

Complete thawing necessary ...................... .................... 28

Thaw houses......................................................... 29

Thaw houses not to be used for storage ................................ 30

Squibs, fuse, and detonators............................................... 30

Means of exploding explosives ........................................ 30

Miner's squibs ....................................................... 30

How sqnibs work...................^..................^.............. 30

Squibs should not be used in fiery mines............................... 30

Fuse ................................................................ 30

Action of fuse..............................................I......... 31

Testing fuse.......................................................... 31

Fuse injured by bad handling.......................................... 31

Care in cutting fuse ................................................... 31

Detonators.....-.-..--....--...-.--..........-...-.-.......-.....-... 31

Advantage in use of detonators........................................ 31

Grades of detonators ................................................. 32

Attaching detonators to fuse .......................................... 32

Fuse not to be used in fiery mines.......... i........................... 32

Fuse and detonators must be of'standard size........................... 32

Electric detonators................................................... 32

Grades of electric detonators .................'......................... 33

Firing electric detonators ............................................. 33

Delay-action electric detonators ....................................... 33

Danger in use of detonators........................................... 34
CONTENTS. 5

Page.

Mining coal with explosives............................................... 34

Conditions in coal mines ............................................... 34

Shooting off the solid.....................'............................ 34

Need of slow-acting explosives........................................ 35

Dependent shots .....................................'................ 35

Overcharging ........................................................ 35

Undercutting and shearing............................................ 36

Shearing............................................................. 36

Charge of explosive in shearing ........'............................... 37

Undercutting ........................................................ 37

Charge in undercutting ......'......................................... 37

Placing of the shots.................................................... 37

Advantage of small charges ............................................ 38

Depth of undercutting ................................................ 38

Care in using permissible explosive's ................................... 39

Dust must be wet down and removed.................................. 39

Humidifying mines................................................... 39

Shot firera ....:............................................-......... 40

Loading and firing charges of explosives................................... 40

Loading bore holes ................................................... 40

Primer .............................................................. 40

Density of charge...............:.:1.................................. 40

Loading black blasting powder........................................ 41

Tamping stick.................................................. ...... 41

Placing fuse and tamping ............................................. 41

Danger of firing untamped holes ...................................... 41

Fitting fuse in detonator.............................................. 41

Fitting fused detonator in primer...................................... 41

Be careful not to pull detonator out of primer ........................... 42

Detonator must not be completely buried .............................. 42

Dirt between cartridges............................................... 42

Fastening electric detonators.......................................... 42

Some explosives, if split and tightly packed, may not explode........... 42

Instructions for tamping..................... I........................ 43

. Air spacing of charge to reduce shattering effect......................... 43

Electric igniter....................................................... 43

Instantaneous fuse.................................................... 44

Delay-action detonators............................................... 44

Safety in single shots time between them ............................. 44

Danger from flame and sparks......................................... 44

Failure of formulas for size of charges.................................. 44

Comparison of effects of different explosives............................ .45

Size of charge of permissible explosives for coal mines .................. 45

Objections to overloading .............................................. 45

Objections to underloading............................................ 45

Premature explosions, misfires and hang fires .......................... 46

Keep away from a hang fire for half an hour........................... 4.6

Partial explosions ..............................................^..... 46

Firing blasts by electricity ................................................ 47

Danger of firing by flame ............................................. 47

Connecting legs to leading wires....-.........----...-.........---..... 47

Splices should not be opposite wrapping splices ....................... 47
6 CONTENTS.

Firing blasts by electricity Continued. Page.

Connecting leading wires to firing machine............................. 47

All connections to be made from bore hole to firing machine............ 47

Connecting detonators in series..'...................................... 47

Connecting holes..................................................... 48

Danger from a break or short circuit................................... 48

Sources of current.................................................... 48

Dry cells............................................................. 48

Portable devices......................... ............................. 49

Testing strength of batteries .......................................... 49

Firing from electric-lighting circuit.................................... 49

Connecting up in parallel............................................. 49

Premature electric firing.............................................. 49

Dynamo-electric machines............................................. 49

Rating of dynamo-electric machines................................... 50

Magnetos............................................................ 50

Leading wires...........................................^............ 50

Insulation of leading wires............................................ 50

Inspection and repair of leading wires after firing.....................'... 50

Testing the line ....................................................... 50

Use of galvanometer................................................... 51

Safety precautions to be taken......................................... 51

Explosives in sinking shafts and blasting rock and dirt...................... 51

Difference in conditions .............................................. 51

Loading, tamping, and firing.......................................... 51

Tamping high explosives .............................................. 52

Proper strength of detonators ......................................... 52

Firing shots in groups ................................................ 52

Firing simultaneously ................................................ 52

Various explosives for use in sinking shafts and driving entries.......... 53

Ammonia dynamites ................................................. 53

Caution in use of ammonia dynamites.................................. 54

Gelatin dynamites!.................-.--....-....---...-.-...-....----- 54

Safe shipment and storage of explosives.................................... 55

Responsibility to public............................................... 55

Federal law and Interstate Commerce Commission regulations ........... 55

Explosives in baggage or household goods.............................. 55

Magazine buildings................................................... 55

Isolation of magazines...............-..........---...-...----......-- 58

Care of magazines.................................................... 58

Appendix................................................................ 60

United States Geological Survey test requirements for explosives ........ 60

Survey publications on mine accidents and explosives................... 61
ILLUSTRATIONS.

Page. 

PLATE I. Gas and dust gallery No. 1, Pittsburg testing station.:...... Frontispiece.

II. Explosion from flour in mills at Minneapolis in 1878............... 12

III. Explosion from coal dust in gas and dust gallery No. 1, Pittsburg

testing station................................................. 14

IV. A, Explosion of high explosive in bomb filled with water; B, screens

for separating different-sized powder grains...................... 16

V. A, Grains of black blasting powder; B, mixture of different-sized

grains of black blasting powder................................. 18

VI. A, Flames from explosion of equal weights of black blasting powder 

and of a permissible explosive; B, boxes of-dynamite, showing 

method of packing it; C, thawer for frozen explosives............ 24

VII. A, Miner's squib; B, miner's squib and fuse....................... 30

VIII. A, Crimping detonator on fuse; B, detonators and electric detonators ........ 1............................................... 32

I.. A, Fuse and detonator fitted into primer; B, secondary battery, firing

machine, and dry cell; C, testing detonator..................... 48

FIGURE 1. Thaw house for frozen explosives; elevation...................... 28

2. Thaw house for frozen explosives; section........................ 29

3. Electric detonator, showing its component parts.................. 33

4. Shooting off the solid........................'................... ' 35

5. Shearing....................................................... 36

6. Snubbing shot.................................................. 37

7. Firstor "buster" shot......................................... 38

8. Bore hole for permissible explosives .......I...................... 39

9. Bore hole ready for firing....................................... 40

10. Loaded bore hole, showing air space about the charge ............ 43

11. Foundation plan, front elevation, and plan of ventilator hole of

brick magazine............................................... 56

12. Sections of magazine............................................ 57

7
NOTE.

This bulletin is issued and distributed in the hope that it may lessen 

the accidents caused by the improper use of explosives in mining 

operations. The Geological Survey will be glad to receive any suggestions as to additions or other changes which, in the opinion of 

readers, would increase the usefulness of this primer in accomplishing 

this purpose.
INTRODUCTION.

By J. A. HOLMES.

Of the common causes of the larger mine accidents, such as falls 

of roof and coal, gas and dust explosions, mine fires, and the misuse of 

explosives, all of which are often closely related, each must be studied 

and fought in a manner peculiar to itself. The last-mentioned, the 

misuse of black powder and other explosives, is sometimes considered

the least important of these causes of mine accidents; but its importance is much greater than the statistics indicate, for the reason 

that the misuse of explosives is the true cause of many of the fatal 

mine fires, gas or dust explosions, and falls of roof that are credited 

to other causes.

Both, the quantity of explosives used and the number of purposes 

to. which they are applied are increasing. They are now made at 

about 150 plants, in different parts of the United States, and the 

product of a single year is estimated at nearly 500,000,000 pounds. 

Nothing in all this material is a safe or "safety" explosive when in 

the hands of a careless or ignorant person; and this is true whether 

considered in connection with the shipment or the use of these 

explosives. In addition to the large losses of life and property 

resulting from an improper use of explosives in mining, the recent 

statistics of the railway bureau for the safe transportation of explosives have shown more than 400 persons killed or injured and over 

$3,000,000 worth of property destroyed by explosives in transit by 

rail. The fact that three years of cooperative effort under the wise 

supervision of this bureau has reduced these losses to almost nothing 

encourages the hope that similar cooperative effort may likewise 

greatly lessen losses of life and property from the use of explosives 

in mining.

The additions to the large death roll of our mines make a recurring 

appeal to the public for fair treatment of the coal-mining industry, 

and to the miner and the manager that they join in every possible 

effort for greater safety. It may. never be possible under conditions 

such 'as exist to-day to prevent mine accidents entirely. Little can 

be accomplished in that direction by either the operators or the 

miners working alone, but experience in all countries shows that

9
10 INTRODUCTION.

through the hearty determined cooperation of both the accidents 

may be greatly reduced. This will require wise laws and regulations 

based on fact and experience, and the strictest possible discipline.

The accidents resulting from the improper use of explosives in 

mining can be most certainly prevented (1) through the use of the 

best and safest explosives; (2) through the handling and firing of 

these explosives in the safest manner by carefully selected and 

trained men; and (3) through the strict and competent oversight of 

these men.

This little book on explosives is published in the hope that it 

may aid in preventing such accidents. The aim has been to tell 

what explosives are and'how they should be handled, with a view 

to greater safety; and to do this in language free of unnecessary 

technicalities. It has been prepared by Charles E. Munroe, consulting 

explosives expert, and Clarence Hall, explosives engineer of the United 

States Geological Survey. It has been revised in the light of suggestions made' by the mining engineers associated with the Survey, by 

several mine managers, by experts associated with the manufacture 

of explosives, and by Col. B. W. Dunn, chief of the bureau for the 

safe transportation of explosives, who has also kindly added a brief 

chapter on the transportation of explosives.

Much, of the information in this primer has been obtained from 

experiments conducted at the mine-accidents station of the United 

States Geological Survey at Pittsburg, authorized by Congress in 

May, 1908, for investigations as to the "causes of mine explosions." 

These investigations have shown the recent development of a new 

type of short-flame explosives, which can be used with greater 

safety than black powder in mines where there is dangerous gas 

or inflammable dust, because the flame from the explosion of black 

powder lasts from. 2,500 to 3,500 times as long as does the. flame 

from these newer explosives, and is therefore more likely to ignite 

the gas or dust in such mines.

Lists of permissible explosives were issued by the Geological Survey 

on May 15 and October 1 of the present year, and with these lists 

was printed a statement of the conditions under which the explosives 

were selected from a larger number offered for examination. These 

lists comprise 31 explosives. There are also in course of publication 

and soon to be issued bulletins dealing with other phases of the subject, such as methods and results of using permissible explosives in 

coal mining, the results of tests of explosives, and the dust problem in 

coal mining.
A PRIMER ON EXPLOSIVES FOR COAL MINERS.

By C. E. MUNROE and CLARENCE HALL.

COMBUSTION AND EXPLOSION.

There is probably no activity of nature with which man is better 

acquainted or has been longer acquainted than with 

fire, of which he has made use from the earliest clays

for warming his body, cooking his food, giving him light, and in more

recent times for breaking down rock, for making steam, and for other

purposes. He has observed that a great number of substances can be

burned, such as wood, charcoal, coal, sulphur, phosCombustible sub- i -i i JT stances phorus, magnesium, zinc, oil and gas in their many 

varieties, and many others, and he has made use of 

them to produce heat and light. He has noticed that when wood is 

burned in large sticks it is difficult to start the fire, and that where 

there are but a few large sticks the fire burns but slowly. When the 

wood is cut into kindlings and these are heaped together, they burn 

more rapidly. When the kindlings are cut into shavings and these 

are piled together, they burn still more rapidly; and when the wood 

is cut into dust by means of a saw and this dust is suspended in the 

air and set on fire, it burns with explosive rapidity.

The same thing is found to be true of the other substances that 

burn under ordinary circumstances and are therefore called combustible. That is, the more finely divided they are and the more 

intimately this finely divided material is mixed with the air, the more 

rapid is the burning or combustion. This intimate mixture with the 

air is best attained with gases such as marsh gas (the fire damp found 

in mines), coal gas such as is used for lighting, and acetylene, or with 

vapors such as those from gasoline; and when these are thus intimately mixed with the air the combustion goes on so rapidly that it 

takes the form of an explosion. Although an explosion

Explosion. i ii i

is thus easily produced by mixing gas or vapors and 

air in the right proportions, explosions may also be obtained by mixing combustible dusts with the air in the right proportions and igniting them; and therefore we are not surprised to hear 

that explosions have been occasioned by mixtures of 

sawdust or flour dust or starch or sugar or soap or coal dust with the

11
12 A PRIMER ON EXPLOSIVES FOR COAL MINERS.

air. Many explosions thus produced are very violent, and destroy 

life and property. (See Pis. II and III.)

In each of the kinds of combustion or explosion that have been

spoken of the combustible substance is mixed with

Air necessary to ajr^ anc[ ^a^ ^ne presence of air is necessary for the

tion. combustion is proved by the fact that when we cut

off the air from contact with a burning body the fire

goes out, or, as we say, we have smothered the fire.

The reason for this has been found in the nature of one of the several different substances that the air is composed of. 

oxygen of the air This is the 'gas named oxygen, which is about onebustion. fifth of the whole volume of the air. It is possible 

to separate this oxygen from the air, and when this 

has been done and burning bodies are brought into contact with 

this separated oxygen it is found that they burn much more rapidly 

than in air, and that the combustion is much more brilliant. By 

repeated experiment it has been proved that all ordinary combust 

tion is caused by the combination of the combustible substance : 

with this oxygen of the atmosphere. Air deprived of its oxygen 

will not support combustion or life.

In view of these facts, and in view, further, of the fact that there 

are other substances in nature besides air that conpeter ^ ^^ Salt" * am oxygen an(^ w^ g^ve UP this oxygen to combustible substances, it would seem probable that combustion could be brought about through the aid of such oxygencontaining bodies; and this was long ago proved to be true. One of 

the first, if not the first, of such bodies that became known to man is 

saltpeter, also called niter, or potassium nitrate, which, because it 

occurs as a white efflorescence like frost on the surface of the soil in 

India, has been called India saltpeter, although it has been found to 

s*ome extent in many parts of the world.

If solid saltpeter in the dry condition is mixed quite thoroughly 

with a solid combustible substance, such as charcoal, 

the mixture burns easily when once it is ignited. 

The advantage of such a mixture is that the oxygen 

which is to support the combustion is in close contact with the charcoal which is to be burned, and that, therefore, this substance or 

mixture can be ignited and will burn without contact with the air, 

and will so continue to burn until the charcoal is completely consumed. As a result of the burning of the charcoal or carbon with 

the oxygen of the saltpeter a gas is formed. As 

charcoal with another result of the burning of 'this mixture of charheat and gas. coal and saltpeter heat is produced, and this heat 

warms up the gas, so that if it is unconfined its volume becomes greatly expanded, and if it is confined it exerts pressure
U. 8. GEOLOGICAL SURVEY 

EXPLOSION FROM FLOUR IN MILLS AT MINNEAPOLIS 
COMBUSTION AND EXPLOSION. 13

and does work. ° Hence, if such a mixture be burned in the bore 

hole of a rock, it may break down the rock, or in the barrel of a gun 

it will drive out the bullet.

It is found, however, that it is not easy to ignite such a mixture of

charcoal and saltpeter, even when mixed in the best

sulphur is added possible way, and to overcome this difficulty use is

to make the mixture , , . , . . ., ignite easily. made of another substance that ignites easily, one 

which on burning gives out heat enough to ignite the 

mixture of charcoal and saltpeter. This substance is sulphur, or 

brimstone, such as has been used in the past for the tips of.sulphur 

or brimstone matches,, for which the same object of easy ignition 

was sought. So eventually the mixture has been made of charcoal 

and saltpeter and sulphur, which are finely ground and closely mixed 

and then formed into .grains, and such a mixture is called gunpowder. 

As has been pointed out, it is simple combustion.that takes place

when such mixtures are set afire, but on account of the thoroughness 

of the mixing, the proportions in which the different substances are 

mixed, and the way in which the material is finally made into grains, 

-this combustion may proceed so rapidly that there is an explosion, 

which is powerful because the solid mixture, occupying a very small 

space, gives on combustion a large volume of highly heated gases. 

About 1821 there was discovered in the desert regions of Peru and 

Chile another saltpeter, sodium nitrate, which has 

come to be known by the name of Chile saltpeter. 

Like the India saltpeter, potassium nitrate, it contains oxygen, and it will give up its oxygen to combustible substances 

with ease at a relatively low temperature. Hence a mixture of it 

with charcoal (known also as carbon) and sulphur makes a body 

similar to that produced with the India saltpeter, and since 1857 such 

a mixture has been extensively used, especially in this country, for 

blasting in rock and in mines.

Besides the India and the Chile saltpeters, many other solid substances that contain oxygen and will give up their 

bod^ief611 ln °ther °xygen easily, on heating, to combustible substances 

have become known, and many of them have been 

tried in the formation of explosive mixtures. Though one or two of 

them are used to some extent, as will be shown further on, none are 

used so largely as the saltpeters.

It has .also been found that we can get the oxygen out of the saltpeters in other ways than by heating an explosive 

saitpeter. aCid frOm mixture, as, for instance, by heating either the India 

or the Chile saltpeter in a proper manner with sulphuric acid, when we obtain from them nitric acid, which contains 

all of the oxygen originally in the saltpeters. It has further been
14 A PRIMER ON EXPLOSIVES FOR COAL MINERS.

o * ' .

learned that when substances like cotton or starch or glycerin are

treated with nitric acid in the proper way there are

Putting oxygen formed, from the cotton, gun cotton, or nitrocellulose. into cotton, glycer- ' J& ' '

in,etc. as it is also 'called; irom the starch, mtrostarch; 

from the glycerin, nitroglycefin; and through this 

means the cotton, the starch, and the glycerin, which are all combustible substances, are converted into substances much more highly 

explosive and more powerful than mixtures made with the saltpeter 

and sulphur and combustible substances. In fact, such bodies can 

be made to explode by a shock such as is produced by a detonato 

or blasting cap when fired in contact with them, and the explosion is 

extremely rapid and very much more powerful than that of the saltpeter mixtures.

It has also been found that by the action of alcohol upon nitricacid solutions of metals, such as copper or silver or mercury, under 

proper precautions, substances may be formed which are still more 

sensitive and still more violent in their explosive effects than guncotton or nitroglycerin. The best known and the 

sensitiveness and most widely used of these substances is fulminate

violence of fulminate J T-I

of mercury. or mercury. When dry, this substance is so sensitive that a very slight blow, very little friction, or a 

slight rise in temperature will cause it to explode, and on explosion 

it produces a shattering effect upon any substance with which it is 

in contact. Moreover, the character of its explosion is such that if 

but a small mass of it is exploded in proper contact with gun cotton 

or nitroglycerin or dynamite or other similar explosive, it will cause 

each of them to undergo a very violent explosion, which also will 

produce a shattering effect on the bodies with which they are in 

contact.

From what has been said it will be seen that there are at least two 

classes of explosives. One class is the saltpeter mixtures, in which 

an explosion is brought about by simple combustion that proceeds 

rapidly and gives rise to a large volume of highly heated gases, though 

almost one-half of the mass remains as a solid residue. Explosives 

of this class exert a relatively slow pushing; effect. Low explosives. 1.11 

upon the substances with which they are in contact 

when they explode, and are called "low" explosives. In the other 

class are explosives of the character of gun cotton and nitroglycerin, 

which undergo explosion by being suddenly and wholly resolved 

into a large volume of highly heated gases, the change proceeding 

many times faster than the combustion that takes place in the saltpeter class of explosives. Because of their speed and power these

explosives have a shattering effect upon the sub- nigh explosives. l T i i i -, stances with which they are in contact, and are known

as "high" explosives, and also sometimes as detonating explosives.
U. S. GEOLOfllCAL SURVEY

EXPLOSION FROM COAL DUST IN GAS AND DUST GALLERY NO. 1, PITTS
EXPLOSIVES. 15

Every explosive, when exploded, exerts pressure in every direction. When laid on top of a rock and exploded, gunconflnement es- powder and other low explosives do not affect the

plosives. rock, because they explode so slowly that the gases

formed can lift the air above them and escape; but

dynamite, fulminate of mercury, and other high explosives, if laid

upon brittle or soft rock and detonated, may shatter it, because they

explode so quickly that the gases formed can not lift the large volume

of air which confines them without pressing back forcibly against the

rock. (See PI. IV, A.) This confinement by air is not, however,

close enough to give the best result with any explosive. By boring

a hole in rock and tamping the explosive firmly in it, gunpowder and

other low explosives may be made to break the rock, or a much less

quantity of high explosive will break the rock than is required to

break it when laid upon it. Confining an explosive is the cheapest

and best way to use it.

It is foolish and dangerous for an inexperienced person to attempt

to manufacture any kind of an explosive except

roily of attempt- under the supervision and direction of a trustworthy

Ing to make explo- . 1 . . r

person who. is skilled in the art. Many serious accidents, which have destroyed lives or inflicted injury 

on persons and property, have been caused by su'ch attempts.

EXPLOSIVES.

As may.be inferred from what has already been said, a large number of substances are known and used as explosives.

Gunpowder. . A .

1 he one longest known and used is gunpowder, which 

has certainly been used since early in the fourteenth century. This 

is made by intimately mixing 75 parts of India saltpeter (potassium nitrate) with 15 parts of charcoal and 10 parts of sulphur. 

Each of these ingredients is ground to a fine powder, and then they 

are ground together while moistened with water, in the proportions 

given, until the mixing is complete. The material is pressed into 

cakes, which are then broken up into grains, which are dried, glazed 

by rubbing, and sorted by the aid of sieves into the various desired 

sizes.

Formerly this India saltpeter powder was used both in guns and

in blasting, and while to-day some of it is used in 

powder blastlne blasting, the larger part of what is used in this

country under the name of black blasting powder is 

composed of 73 parts of Chile saltpeter (sodium nitrate or nitrate of 

soda), 16 parts of- charcoal, and 11 parts of sulphur. This black blasting powder is made in a manner similar to that described for gunpowder, but less time is spent in making the mixture, and the charcoal is 

usually obtained from coarser-grained woods. The Chile saltpeter will
16' A PKIMER ON EXPLOSIVES FOR COAL MINERS.

supply more oxygen, and supply it more easily, than the India 

saltpeter, and therefore is a better and cheaper oxidizing agent; but 

the Chile saltpeter is not used in the manufacture of gunpowder 

because when it is exposed to moist air it takes up water by absorption

from the air and becomes wet, and powder or other 

from explosives in which this Chile saltpeter (nitrate

of soda) is used likewise take up moisture when 

exposed to the air and become damp, so that it is difficult, and 

sometimes impossible, to set fire to them. As gunpowder for 

use in guns and firearms must often be kept for a great many 

years, and yet always be in such condition that it can be fired 

at any moment with certainty, this property of absorbing moisture 

from the air makes the nitrate of soda unfit for use in gunpowder;

but blasting powder is not expected to be stored for

Keep powder dry. i , , , -11

years, and in magazines at mines it is quite possible 

to store it for a while so as to protect it from exposure to damp air. 

Besides, by proper management it is possible to obtain this blasting 

powder fresh from the manufacturer and use it promptly while in 

that condition; hence advantage may be taken, for economic use, 

of the superior efficiency and cheapness of the nitrate of soda in 

the manufacture of blasting powders if we keep them dry.

Black blasting powder comes into the market in the form of grains

whose edges have been rounded off by rubbing

owal* U l * * * n § together in a revolving barrel and which are usually

coated on the surface, or glazed, as it is termed,

with graphite, or black lead. The object in rounding and glazing

the grains is to render them free running, and the glazing also

serves to delay somewhat the taking up of moisture from the air by

the grains.

The powder is divided into grades according to the size of grains, 

as separated and collected by sieves of different sizes 

gS. °f P°Wder of openings. (See PL IV, £.) The sizes most usually offered for sale are called CC, C, F, FF, FFF, 

and FFFF. Of these, CC represents the largest grains, about onehalf inch in diameter, and FFFF represents the smallest grains, 

about one-sixteenth inch in diameter. (See PI. V, A.) The 

relation between the letters designating the sizes of the powder 

grains and the sieves by which the different sizes are separated is 

shown in the following table:
U. S. GEOLOGICAL SURVEY

A. EXPLOSION OF HIGH EXPLOSIVE IN BOMB FILLED WITH WATER.

B. SCREENS FOR SEPARATING DIFFERENT-SIZED POWDER GRAINS.
EXPLOSIVES. 17

Relation between sizes of black blasting powder and separating sieves.

Size of

grains.

CO

C

F

FF

FFF

FFFF

Diameter of

round holes

in screens

through 

which grains

pass.

$inch

iMnch

J inch

A inch

Jinch

A inch

Diameter of

round holes

in screens

on which 

grains

collect.

£ inch

4 inch

iinch

J inch

A inch

,,' inch a

a Square holes

To get the best results in the use of this powder in blasting, the

grains should be of uniform size, so that the miner,

Danger in using a having determined the best size of charge; may have

mixture of different ° . . TT -, . ,

sized grains. no difficulty in repeating it. Unfortunately, not 

enough care is taken in separating the grains into the 

different sizes, and powders have appeared in the market in which 

a considerable number of different sizes of grains were mixed 

together, so that the miner has obtained quite different results 

from his different shots in the same mine of coal with the same 

grade of powder. (See PL V, B.} Moreover, where large and small 

grains of powder are mixed in a charge, the fine grains, which burn 

freely, may produce, in burning, enough pressure to throw the large 

grains out into the mine where they can set the gas and dust afire. 

This makes such a mixture of grains a dangerous one in use.

It has already been said, that many other substances besides 

India saltpeter (potassium nitrate) and Chile saltpeter 

chl°" (sodium nitrate) are known which contain oxygen in 

such quantity and in such manner that they may be 

used as the oxidizing agents in forming explosives. Among these 

is the substance known as potassium chlorate. More than one 

hundred years ago- an eminent French chemist showed that when 

it was mixed with combustible substances a most powerful explosive 

was produced; but, unfortunately, this mixture was found to be 

so sensitive to friction, blows, and heat as to endanger the lives of 

those who sought to handle and use it. Many of the mixtures 

produced with potassium chlorate are so easy to prepare and explode 

with such violence that a great many persons have been tempted 

to make them, but until recently all those that have been devised 

have been rejected as unfit for use because they were liable to destroy 

those who attempted to make or use them. It is found, however, 

that when dry and finely ground potassium chlorate is mixed with 

a body like starch, and with oil and other substances, an explosive 

16210 Bull. 423 09 2

Potassium 

rate.
18 A PRIMER ON EXPLOSIVES FOK COAL MINERS.

is produced that is fairly safe to handle. Mixtures of this nature 

have met with some use in Europe.

Attention has also been called (p. 14) to the fact that when purified drv cotton is immersed in nitric acid in the

Nitrocellulose. J . '-, i , i T

proper manner it is changed into an explosive substance through reaction with the nitric acid. When we withdraw the 

fibrous cotton from the nitric acid, wash it thoroughly to remove any 

acid that sticks to it, and then carefully dry it at a low temperature, 

the cotton appears unchanged to the eye, even when examined most 

carefully. It has, however, become a little harsh to the touch. 

When rubbed, it becomes electrified so that it sticks to the fingers, 

and when a flame is applied to it, it flashes off with great rapidity. 

In practice, a mixture of sulphuric acid is used with the nitric acid in 

nitrating the cotton. By varying the strength and the proportions of 

the nitric and sulphuric acids, their temperature when the cotton is 

dipped in them, and the length of time that the cotton is in them, 

we can get a number of different products varying in the rate at 

which they will burn and in the degree to which they are soluble in 

various solvents; but every such product results from the replacement of more or less of the element known as hydrogen, which was 

present in the cotton, by nitrogen and oxygen (indicated by the 

formula N02), which came from the nitric acid. Such a product, 

obtained by the action of the nitric acid on the cotton, will take 

fire and burn the more easily the greater the number of N02 groups 

that have replaced hydrogen in the cotton. We may, for convenience, divide these various products into two classes. Those 

which contain the fewer of these N02 groups are called pyroxylin, or 

soluble nitrocellulose, or collodion cotton, and those which contain 

the greater number of the N02 groups are known as gun cotton. In

the manufacture of gun cotton the very strongest nitric and sulphuric 

acids are used. After the product has been washed so as to remove 

most of the acid sticking to it, it is pulped while wet into a fine powder 

in a machine such as is used in pulping paper stock, and when the 

gun cotton has been washed in this powdered condition so as to 

remove the last traces of acid, it is molded into blocks or sticks and 

is used as an explosive in that form.

Nitroglycerin is prepared by slowly running glycerin into a 

mixture of the strongest nitric and sulphuric acids,

Nitroglycerin. i i i i i

the whole being stirred and kept cool during the 

process of mixing. The reaction which takes place between the 

glycerin and the nitric acid is similar to that which takes place with 

the cotton. As a result of the reaction, N02 groups from the nitric 

acid replace hydrogen in the glycerin, and the mild, sweet, harmless 

glycerin is thereby changed into the powerful and dangerous explosive nitroglycerin. Nitroglycerin is a rather dense, oil-like liquid.
U. S. GEOLOGICAL SURVEY

FFFF FFF

cc

A. GRAINS OF BLACK BLASTING POWDER. B. MIX
EXPLOSIVES. 19'

When pure it is colorless, but as it appears in the market it is usually 

pale yellow. It is somewhat poisonous, and one can be poisoned by 

it not only through the mouth but also by breathing its vapors or by 

allowing the liquid to touch the skin. A drop of it touching the tip 

of the finger will usually soon produce a violent headache. Fortunately, most persons lose their sensitiveness to poisoning after 

repeated contact, so that they cease to have the headache, but it

would still be dangerous for these persons to get any 

freezes'° glyCerl11 °^ ^ne nitroglycerin into the mouth. Nitroglycerin

may freeze after some exposure to a temperature of 

52° F. (see p. 26) and it must be thawed before it can be properly 

used as an explosive.

Being a liquid, nitroglycerin is especially dangerous for ordinary

use, because it may escape from the cans or other 

Liquid nitro- vessels in which it is carried or stored and run off

glycerin is especially .

dangerous. to considerable distances, so as to increase the chances 

of accidental explosion by a blow, or friction, or heat; 

and also because it may, when placed in a bore hole, leak out into 

crevices or seams in the rock, and when fired give most undesirable 

results. In fact, during the middle of the last century, when it was 

offered for use, so many accidents occurred that many countries, by 

law, forbade its use or manufacture. We can, however, prevent a 

liquid from flowing about by absorbing it in a porous body, like a 

sponge. This has been done with nitroglycerin, and the product is 

called dynamite. Dynamite consists of nitroglycerin 

absorbed in a solid body called the dope. There are 

many dynamites. One of the earliest known and used was made by 

absorbing the nitroglycerin in powdered "rotten stone." As the 

"rotten stone" could neither burn nor explode, it was called an inactive dope, and there are several varieties of dynamites with inactive dopes. On the other hand, nitroglycerin may be absorbed in 

gunpowder. As the gunpowder explodes, as well as the nitroglycerin, 

when the dynamite is fired, the gunpowder is called an active dope. 

There are a large number of dynamites made with active dopes, and 

with varying percentages of nitroglycerin. The standard straight 

dynamite used at the Pittsburg testing station may be taken as an 

example of a dynamite with an active dope. It consists of the 

following:

Composition of standard straight dynamite.

Per cent.

Nitroglycerin................................................... 40

Nitrate of sodium................................................ 44

Wood pulp..........................:............................ 15

Calcium carbonate............................................... 1

100
'20 A PRIMER ON EXPLOSIVES FOR COAL MINERS.

Since it is a liquid, nitroglycerin, like other liquids, acts as a solvent, and it has been found that under certain congelatin diticms it can dissolve soluble nitrocellulose, and that 

mite. the mixture thus formed will set to a jelly-like 

mass. In this way, or sometimes by the use of 

other solvents also, the substance known as explosive gelatin is 

formed, a substance that in some respects is regarded as the most 

nearly "ideal" explosive. However, it is too powerful for ordinary 

use in blasting, and it is therefore diluted by mixing it with a dope, 

such as the nitrate of soda and wood pulp used in straight dynamite. The mixture so formed is known as gelatin dynamite.

It has already been said that nitroglycerin when exposed to 

AII explosives con- ordinary winter temperatures will freeze. Dynamite, 

taining nitroglycerin explosive gelatin, and gelatin dynamite will also 

freeze>. freeze, because all of them contain nitroglycerin, and, 

like nitroglycerin, all of these substances should be properly thawed 

before any attempt is made to use them.

Each of these substances is put upon the market in the form of 

sticks or cartridges, which are made by wrapping 

rt" UP cylinders of the material in paper. The wrappers for dynamite and gelatin dynamite are paraffined to protect them from the action of water and the moisture in 

the air, because they contain nitrate of soda and hence may absorb 

moisture and become spoiled, and develop new sources of danger 

in handling and use. These sticks usually vary in size from seveneighths inch to 2% inches in diameter, and they are usually 8 inches 

. long. They are usually packed in cases containing

Packing dynamite. to J i «m- -j »

50 pounds each. The mark Ihis side up, or a

design on the top of the case, shows the position in which the cartridges are packed. The cases should always be placed so that the 

cartridges lie on their sides, and they do lie so when the cases are 

stored with their top sides up.

For use in coal mines it is suggested that the explosive be packed 

in cases or cartons containing the weight which the law of the district 

permits being taken into the mine. (See PL VI, B.)

Besides cotton and glycerin, there are a large number of substances,

such as sugar and starch, that are chemically related to cotton and

glycerin and through the action of nitric acid, particularly in the

presence of sulphuric acid, give rise to explosive substances. Many

of these have been produced, but so-called nitrostarch

is the only one that seems to have any commercial

importance. During the last ten years this has attracted some

attention, and it has been offered for use both in this country and in

Europe. It is a finely powdered substance like starch itself, but it

does not need, as starch does, to be suspended in the air in order to
EXPLOSIVES. 21

explode on ignition, because even when in a pile it will burn with 

great rapidity i'f set afire, and through the action of a detonator it 

explodes with great violence. It is not yet used by itself, but is 

used as a component in various explosive mixtures, particularly 

dynamites.

Attention has been called to the use of potassium nitrate and sodium nitrate in the manufacture of explosives. In 

nl~ recent years another nitrate, formed by the union 

of ammonia with nitric acid and known as ammonium nitrate, has come to be somewhat largely used. It has been 

used in this country for more than a quarter of a century in the manufacture of some' dynamites, taking the place of .sodium nitrate and 

having the advantage over it that on explosion it goes completely 

into gases; but it has come to be used in Europe in the manufacture 

of special explosives for use in coal mines, for the reason that on explosion it forms a large amount of water, and this lowers the temperature of all the products of the explosion. In the making of several of these ammonium-nitrate powders, various substances obtained from coal tar, which generally have been acted upon by nitric 

acid, are mixed with the ammonium nitrate.

The substances derived from the coal tar, after having been acted 

upon by the nitric acid, are known as nitro-substitu- 

^on compounds. One of the substances obtained 

from coal tar which is perhaps best and longest 

known is carbolic acid, and when this reacts with strong nitric acid 

it gives us the nitro-substitution compound known as picric acid. 

Other substances obtained from coal tar that are pretty well known 

are benzene, toluene, and naphthalene. When these are acted upon 

by nitric acid we obtain from them the nitro-substitution compounds 

known as nitrobenzene, nitrotoluene, and nitronaphthalene. These 

are but a few of the many substances that may be obtained from 

coal tar and furnish, through the action of nitric acid upon them, 

nitro-substitution compounds. All the nitro-substitution compounds will form explosives when mixed with oxidizing agents such 

as ammonium nitrate, or other nitrates, or clllorates, and many explosives have been made from such mixtures. Moreover, these 

nitro-substitution compounds have been used as components of 

dynamites, particularly because they lower the freezing point of the 

nitroglycerin in the dynamites.

The nitro-substitution compounds are so called because the N02

groups in them, obtained from the nitric acid, are

why nitro-substi- directly connected to the carbon atoms in the original

tutlon compounds . , . . °

are so called. material, replacing hydrogen atoms; whereas iri gun

cotton, nitroglycerin, and bodies of that sort, the

N02 groups are linked to the carbon atoms of the original substance
22 A PRIMER ON EXPLOSIVES FOR COAL MINERS.

by means of atoms of oxygen. The nitro-substitution compounds 

are usually yellowish to red crystalline solids, but as most of these 

solids are easily melted, they are often sent out in compact masses. 

A few of them are liquids at ordinary temperatures, and they have 

a marked aromatic odor. Some of these substances are poisonous. 

Great care should be taken in handling all of them, and one should 

especially avoid breathing their vapors.

As has been stated above, the most common fulminates are produced by dissolving a metal, such as mercury, in a

Fulminates. J. . -, -, i , .

strong nitric acid, and pouring the solution into 

common alcohol. When the proportions used are correct and the 

operation is carried out in a proper manner, after an apparently violent reaction there will be produced a mass of fine, gray crystals that 

look quite alike, and this is known as fulminate of mercury, or mercury fulminate. The crystalline powder thus produced is washed with 

water to free it from acids, and because of its extreme sensitiveness 

it is kept soaked with water until desired for use. It is principally 

used in loading blasting caps or detonators, and for this purpose the 

water may be removed from it by alcohol and- it may be loaded into 

the copper capsules while wet with alcohol, but it should be always 

borne in mind that this .mercury fulminate, even when thoroughly

soaked with or sunk under water or alcohol, will 

minateT1 WUh ful~ expl°de w*th tremendous violence if only a small

amount of the dry fulminate be exploded while 

touching it, or very near it. Hence extreme precautions should 

always.be taken with mercury fulminate, whether the substance be 

wet or dry.

The manufacture of explosives is by no means simple. Unless all

the materials are of the proper kind and in the proper 

warning against condition, and they are used, in the proper order, in manufacturing ex- 11 ^11 plosives. the proper manner, with the proper tools and vessels, 

and with all the proper precautions at each stage of 

the operation, the manufacture is a very dangerous thing to undertake, and it is very foolish for anyone to undertake it by himself.

EXPLOSIVES FOR USE IN COAL MINES.

It is evident that a large number of different explosives can be 

formed by mixing various combustible substances 

with various oxidizing agents, or by using such mixtures as dopes for dynamite, or by using them together 

with the different nitro-substitution compounds. In fact, the number is "so great that a book published in 1895 gave the names of more 

than one thousand different explosives, and many have been added to 

the list since that date. As the number of those in actual use is much 

smaller, it is clear that most of the explosives known are, for various

Number of explosives.
EXPLOSIVES FOR USE IN COAL MINES. 23

reasons, unsuitable for use; indeed, no one of those more generally 

known is suitable for use under all circumstances. For instance, 

some of them on explosion give off a considerable volume of flame; 

some of them on explosion give off considerable volumes of poisonous 

or noxious gases; some of them explode so quickly as to shatter the 

rock or other material in which they are fired and break it down into 

fine pieces; some of them are too bulky; and so on.

It is evident that if we are seeking to break down the rock in an

open quarry for the purpose of making use of that

Explosives in open r ^ ag ballast for roads, we can employ an explosive

work. ' . . '

that produces a long flame, or gives off poisonous gases, 

or shatters the material, because the work is done in the open air, 

and because the rock has to be broken up into small pieces anyway, so that it is well for the explosive to do it. If, however, we 

sought to get out from that quarry blocks of stone such as marble or

granite, which were to be used in building or for monuments, we

should avoid using the shattering explosive and choose one that

slowly, and without a shock, separates the rock mass from the

deposit. Yet for this purpose also, as the work is in the open

air, it might matter little if the explosive gave rise to a large flame

or gave off poisonous gases, provided the quantity of explosive used

was small. But the conditions in a coal mine are

Explosives in in- very different from those in a quarry. The mine is

closed work. J . .

inclosed and not out in the open air, and, moreover, it 

is liable at any time to contain inflammable gases or coal dust, or both, 

which may form explosive mixtures with the air. If under these

circumstances an explosive were used which gave off

a long flame °n firin& this flame> darting Out from

the bore hole, might set fire to the explosive mixture 

in the mine and produce a mine explosion. (See PL VI, A.) 

Moreover, as the mine is an inclosed space and as the wholesomeness of the air within it depends upon artificial venNoxlous gases. . , * .

tilation, it is also objectionable in such a mine to 

make use of an explosive giving off any considerable quantity of 

noxious gases, which must be removed from the mine after the 

explosion before the miner can safely return to his work. 

Considerations -such as these have led to an investigation by the 

United States Geological Survey of the explosives 

°^QrQ^ m tne market, for the purpose of determining, 

in the interest of the coal miner, which of such explosives are suitable for use in coal mines and will do the work 

with the greatest degree of safety for the miner using them. Of 

course, it is impossible to insure complete safety, for no explosive 

can be perfectly safe and every explosive should be treated with the 

greatest care and consideration.
24 A PEIMEE ON EXPLOSIVES FOR COAL MINERS.

With this object in view the United States Geological Survey has 

established a testing station at Pittsburg, Pa. (see

Testing station at _, T . . ° r , \

pittsburg. rl. 1, frontispiece), where there has been erected a 

^Explosives gallery jarge gallery made of steel, 100 feet long by 6 feet

4 inches in diameter, and so made that it can be 

filled with fire damp, or with coal dust and air mixed, or with 

gas, dust, and air mixed in any desired proportion, so as to reproduce the dangerous conditions that may occur in coal mines. 

Attached to one end of the gallery is a very strong "gun" 

with a chamber representing the bore hole in a mine. From this 

"gun" various exactly determined quantities of the explosive to be 

tested may be fired, either untamped or tamped, into 'the. mixture 

in the gallery, and thereby it can be learned whether or not the 

definitely known quantity of explosive used as described will cause 

the ignition and explosion of the mixture in the gallery. Besides 

this gas and dust gallery there is at the testing station a collection 

of other apparatus and appliances by which to test the various 

properties of explosives, and so to find their relative value and their 

relative- safety for use in coal mines. This investigation has been 

going on since September, 1908, and there have already been published two lists of explosives that have passed all test requirements 

in a satisfactory manner and are considered to be suitable for use in 

coal mines, provided they are used under the prescribed conditions. 0 

These approved explosives are, therefore, called by the United

States Geological Survey "permissible explosives."

^Permissible explo- rphe name Qf each brand that hag pagsed the tegtg

up to October 1, 1909, together with the name of 

the manufacturer, is given in the following list:

List of permissible explosives October 1,1909.

Brand. Manufacturer.

.ffitna coal powder A... 

JEtna coal powder A A. 

./Etna coal powder B... 

./Etna coal powder C... 

Bituminite No. 1......

Black Diamond No. 3.. 

Black Diamond No. 4.. 

Carbonite No. 1........

Carbonite No. 2......

Carbonite No. 3......

Carbonite No. 1-L. F. 

Carbonite No. 2-L. F. 

Coalite No. 1.........

Coalite No. 2-D.

Coal special No. 1......

Coal special No. 2......

Collier dynamite No. 2.

Collier dynamite No. 4. 

Collier dynamite No. 5.

..Etna Powder Co., Chicago. 111.

Do.

Do.

Do.

Jefferson Powder Co., Birmingham, Ala. 

Illinois Powder Manufacturing Co.. St. Louis, Mo.

Do.

E. I. Du Pont de Nemours Powder Co., Wilmington, Del.

Do.

Do.

Do.

Do. 

Potts Powder Co., New York City.

Do.

Keystone Powder Manufacturing Co., Emporium, Pa.

Do.

Sinnamahoning Powder Manufacturing Co., Emporium, Pa.

Do.

Do.

See p. 60 for prescribed conditions under which each of these explosives is to be used.
U. S. GEOLOGICAL SURVEY

R. P. M. 375. Duration of flame, 1539 miIIisec.;height of flameSO.EI in. 

A BLACK BLASTING POWDER

R.P. M. 2400. Duration of flame, .342 millisec.; height of flame, 19.79 in. 

A PERMISSIBLE EXPLOSIVE

A. FLAMES FROM EXPLOSION OF EQUAL WEIGHTS OF BLACK BLASTING POWDER AND OF A

PERMISSIBLE EXPLOSIVE.

B. BOXES OF DYNAMITE, SHOWING METHOD OF PACKING IT.

C. THAWER FOR FROZEN EXPLOSIVES.
EXPLOSIVES FOR USE IK COAL MIKES. 25 

List of permissible explosives October 1, .7909 Continued.

Brand. Manufacturer.

Giant A low-flame dynamite. 

Giant B low-flame dynamite. 

Giant C low-flame dynamite. 

MasuriteM. L. F............

Meteor dynamite............

Mine-He A. 

Mine-He B. 

Monobel...

Tunnelite No. 5. 

Tunnelite No. 0. 

Tunnelite No. 7. 

Tuunelite No. 8.

Giant Powder Co. (Consolidated), Giant, Cal.

Do.

Do.

Masurite Explosives Co., Sharon, Pa. 

E. I. Du Pont de Nemours Powder Co., Wilmington, Del. 

Burton Powder Co., Pittsburg, Pa.

Do. 

E. I. Du Pont de Nemours Powder Co., Wilmington, Del. 

G. R. McAbee Powder and Oil Co., Pittsburg, Pa.

Do.

Do.

Do.

With reference to the characteristic component of each of these 

permissible explosives, they may be placed in three

classification of classes ammonium nitrate powders, represented by

e exp ° ^Etna coal powder AA, Collier dynamite No. 5, Masurite M. L. F., and Monobel; hydrated powders, represented by Meteor dynamite and Giant A, B, and C; and nitroglycerin powders, represented by all the others on the list. With the 

exception of Masurite M. L. F., all the powders mentioned in the list 

contain nitroglycerin, and therefore they are all of the general nature 

of dynamite; but the components and proportions of the dope have 

been so chosen and the mixtures so made as to modify very greatly 

the shattering effect upon explosion, while at the same time the volumes of gases produced are relatively cool. As a result, the flames

produced are short and not lasting, and coal is thrown

Advantages of ou£ without being powdered, when the proper charge

permissible explo- .. .

of such an explosive is used and this charge is properly placed. These explosives are designed to take 

the place of black blasting powder, which has been found to be 

unsuited for use in coal mines where dangerous gas or inflammable 

dust is present, because of the great mass of flame which it produces 

and the long time that this flame lasts, and because of the quantity 

of poisonous smoke and noxious gases which it gives out when 

exploded. Although explosives of the kind represented in the list 

of permissible explosives have been introduced into this country only. 

during the last few years, yet their consumption now amounts to 

several million pounds annually and is rapidly growing.

Unfortunately, though the permissible explosives are good coal 

getters and yield short flames that do not last and 

gases °f l°w temperature, so that there is little danger of igniting the explosive gases and dusts in mines 

when they are used, still the gases they yield on explosion may be 

noxious and inflammable; and miners are warned, when using permissible explosives, not to return to the breast after firing them any
26 A PEIMEE ON EXPLOSIVES FOE COAL MINEES.

sooner than they would if they had fired a charge of black blasting 

powder.

From what has been said regarding nitroglycerin, it follows that

all these permissible explosives, except Masurite M.

L- Fv wil1 freeze when exposed long enough to low

temperatures, and they must be thawed before they 

can be properly used. It is true that in making several of them, 

especially those marked L. F., materials have been added that prevent their freezing so readily, but the manufacturers do not claim 

that such explosives will remain unfrozen when the temperature falls 

below 35° F. To keep any of the nitroglycerin explosives permanently thawed, they should be stored where the temperature does 

not go below 52° F. On the other hand, care should be taken that

none of these explosives is subjected to high ternDanger from ex- peratures, for this will render all of them more

posure to high tern- x . . . .

peratures. sensitive to explosion and is likely to cause the decomposition of some of them. It is best that the 

temperature of magazines in which they are stored should not rise 

above 90° F.

Explosives should not be exposed for any length of time to direct 

sunlight, because this may lead to decomposition in 

sunlight* expose to those containing nitroglycerin, nitrocellulose, nitrostarch, or substances of that kind. Explosives should 

be stored in a dry place, for many of them contain considerable 

quantities of ammonium nitrate or of sodium nitrate and so will 

take up moisture from damp air and become damp. Too great 

dampness makes the explosive not only harder to 

^Keep explosives g^ j^ wea]jer wnen fired. Besides, if the explosive is damp the nature of the gases produced will be 

different. Moreover, as bodies like dynamite become moist, the 

nitroglycerin contained in them tends to run out; that is, what is 

called exudation takes place, and all the dangers follow that belong 

to liquid nitroglycerin.

On the other hand, explosives should not be kept in an extremely 

dry place, for all of them, as made, contain some 

moisture, and if the place of storage is very dry the 

explosive may lose this moisture. Such a change 

in composition will affect the explosive so as to change the speed 

with which the explosive reaction takes place within it, and 

therefore the character of the work which it does when exploded. 

Naturally, the longer an explosive is kept in storage 

promptly Pl ° SlTeS ^ne grater are the chances that change will take 

place in it, and therefore the explosive should be 

obtained in as fresh a condition as possible and should be used as 

soon as possible after it is received. -Also, it should be kept stored
EXPLOSIVES FOR USE IN COAL MINES. 27

in its original packages in the magazine outside the mine until 

wanted for immediate use, and then used promptly.

Dynamite is put up in sticks, which are wrapped in paper, and

the cartridges so formed are usually dipped in paraffin

injury to car- £0 make the wrapping waterproof. As by rough

tridges from rough \A ° 11,1 i

handling. handling the folded, edges may be broken open and 

the contents of the cartridge thereby exposed to the 

moisture of the air, these cartridges should be handled with great 

care, and they are best carried to the place where they are to be used 

in the cartons in which they are bought.

In handling explosives the greatest care must be taken to prevent 

their falling or getting shocks. They must not be 

cartridges handllne thrown or dropped, and portions of the powder falling from the cartridges must be carefully guarded 

against friction, blows, or fire.

Explosives should never be carried by railroad except in conformity with the rules of the Interstate Commerce Comsivse^lpmentofexpl°" mission, as published by the American Railway 

- Association, These rules make it unlawful to carry 

any explosives, except small-arms ammunition, on any public vessel 

or vehicle carrying passengers.

Explosives should be stored in properly placed, built, and aired 

magazines. Such a magazine should be far enough 

sifes°raee °f 6XPl °" fr°m other buildings or works so that if an accidental 

explosion occurred when the magazine was full it 

would do the least possible damage, and it should be so placed as not 

to be in danger from forest, brush, or other accidental fires. Magazines are best built of brick or concrete, but they are 

. more frequently built of wood covered with corrugated iron. In any case they should be provided with wooden floors, 

which should be kept free from grit and dirt. It is best that only 

one kind of explosive should be kept in any one magazine. If more 

than one kind of explosive (other than permissible explosives) must, 

be kept in the same magazine, the magazine should be divided into 

rooms, by partitions, and the different explosives 

Detonators never jjep^ m different rooms. On no account should deto be stored with x 11- ^ other explosives. tonators, or blasting caps, or any device containing 

fulminating composition, be kept in the same magazine with any other explosive. These firing devices should be kept 

in a dry place by themselves.

Plans and specifications for magazines will be furnished by manufacturers of permissible explosives. (See also pp. 57-59, and figs. 

11 and 12.)
A PEIMER ON EXPLOSIVES FOE COAL MINERS.

Opening 

explosives.

°*

r

Thawing 

explosives.

frozen

Window for 

thermometer

The greatest care must be taken to prevent packages of explosives 

from falling or getting shocks. They must not be thrown, dropped, 

nor. rolled. Wooden boxes containing explosives 

should be opened with extreme care, so as to avoid 

friction and blows as much as possible. They should 

never be opened within the magazine, but in a properly sheltered 

place outside of the magazine and at a distance from it. They should 

be opened only by the use of a wooden mallet and a hardwood wedge.

The thawing of frozen explosives 

requires extreme care, and doing it 

improperly has frequently led to most 

serious accidents. 

No attempt should ever be made 

to thaw a frozen explosive by placing the cartridge before a fire, or 

near a boiler, or on steam pipes, or 

putting it in hot water, or by placing it in the sun. While thawing, 

nitroglycerin explosives are extremely sensitive and should be 

handled with -great care. During 

the thawing the nitroglycerin tends 

to separate from the dope and run 

out from the cartridge (that is, to 

exude), and this is a source of 

danger.

When but a small amount of 

the explosive is required, it may be 

thawed in the thawers that are furnished by all the manufacturers of 

explosives and have been found safe 

,for use as directed. (See PI. VI, <7.) The thawer consists of a waterjacketed tin vessel, in which the cartridges are 

plosives?" °r e*~ placed and which is closed with a tin cover. Before 

the water is placed in the vessel it is warmed up to a 

temperature not uncomfortable to the hand put into it, and the 

cartridges are allowed to remain in the thawer until it is found, by 

gently pressing them, that they are completely thawed throughout. When thawed, the material will feel plastic, or like flour, 

between the fingers. When frozen, or partly frozen, the stick 

will feel more or less rigid and hard. It is necesnecessary!6 &WinS saiT that ^ne stick should be thawed completely, 

because dynamite when frozen can be detonated 

only with great difficulty, and any part that is frozen will be

O 1 Z 3 4 FEET

FIGURE l. Thaw house for frozen explosives; 

elevation.
EXPLOSIVES FOR USE IN COAL MINES. 29

but imperfectly detonated in the hole; hence not only may such 

partly frozen powder fail to give its full effect as an explosive, but 

there is danger of a serious accident in a coal mine where such powder 

is used, because if a blown-out shot results the burning solid part may 

set fire to the dust or fire damp in the air of the mine.

Where large quantities of explosives are used daily, a small thaw

house should be provided for the purpose of thawing

out the frozen explosive. (See figs. 1 and 2.) Plans

and specifications, together with a bill of material for such a thaw

mi

ss :

To o o o o~o o o! 

o o o o o o o

JO O C O O O O C)

oooooocoi

::SS

SECTION E-F

SECTION C-D

FIGURE 2. Thaw house for frozen explosives;- section.

house, will be furnished, on application, by the manufacturers of 

permissible explosives. The thaw house should be large enough to 

hold all the explosives used in one day's work. It should be heated 

by a small hot-water heater, placed at least 4 yards from the house, 

the hot water being passed into the house through iron pipes, at such 

a rate that the temperature in the house will not at any time be above 90° F. '
30 A PEIMER ON EXPLOSIVES FOE COAL MINERS.

Thaw houses are intended only for the treatment of explosives for

immediate use, and not for the storage of explosives,

Thaw houses not for if powders or dynamites are left in this high temto be used for stor- r j j t i ui * 4.1

age. perature and dry air tor a considerable time, the 

moisture that is a proper part of them will be driven 

off, and, as stated before, this will markedly alter the character of 

the powder or dynamite and may lead to accidents in its use.

SQUIBS, FUSE, AND DETONATORS.

It has been made clear in the discussion of combustion and explosion and the description of various explosives that they 

can ^e cause(l to explode by various means. All of 

them can, under some circumstances, be made to 

explode by fire. Some of them can be caused to undergo a detonating 

explosion by setting off a detonator in contact with them. In blasting 

use is made of both these means for setting off explosives, the means 

used being determined by circumstances.

In setting off by means of fire, use is made of miner's squibs, or of 

fuse. Miner's squibs (PI. VII, A) consist of tapering

Miner's squibs. \ . £ii i -,i £

paper tubes about 7 inches long, rilled with line gunpowder, one end of each paper tube being treated with chemicals 

so as to form a slow-burning match, which, when ignited, burns so 

slowly as to give the miner time to reach a place of safety before 

the explosion. When used the squib is placed in the needle hole, 

or blasting barrel, through the tamping, with the match end of the 

squib outward. When the match is ignited the fire burns slowly

along the tube until it reaches the powder core.

Then the squib darts forward like a rocket, leaving 

a trail of flame behind which spurts out from the needle hole, and

the fire continues burning along the powder core of the squib until it 

bursts out of the other end of the tube and so ignites the charge. 

In experiments made at the Pittsburg testing station it has been 

found that, though the burning match on the end of

squibs should not ^e ^u]-)e O f ^}ie Sq Uib does not inflame a mixture of

be used inflery. , . mines. mine gas and air, as soon as the powder core is 

ignited the flame that then flashes out from the end 

of the squib will explode the mixture. Hence squibs should not be 

used in any gaseous mine.

Fuse, as used in coal mines, is sent out into the market in coils

50 feet long, and in several varieties, but all consist

of a core of mealed gunpowder inclosed in two or

more layers of yarn and generally surrounded by tape that has

been dipped in a waterproofing composition. (See PI. VII, B.)

Some varieties are then dusted with substances like powdered soapstone, to prevent the sticky surfaces from sticking to one another.
U. 6. GEOLOGICAL SURVEY

A. MINER'S SQUIB.

B. MINER'S SQUIB AND FUSE.
SQUIBS, FUSE, AND DETONATORS. 31

The kinds of fuse most commonly used are hemp fuse, cotton fuse, 

single-tape fuse, double-tape fuse, triple-tape fuse. 

When one end of a fuse of any variety is lighted the powder core 

burns slowly along the fuse till at last the flame 

rushes out at the farther end and, if it touches a 

charge of powder, sets it off. Like squibs, fuse throws off flame 

when lighted, and hence the use of fuse in a gaseous mine can 

not be recommended. Fuse should be so made and should be 

in suqh a condition when used that any part of 

any coil will burn at the rate of 1 foot in eighteen to. 

twenty seconds. This is of the greatest importance, because in 

setting a charge the blaster or shot firer cuts a piece of fuse to reach 

from the charge to the opening and long enough to give hiin ample 

time, after the end has been set on fire, to reach a place of safety 

before the flame fires the charge. Therefore, careful tests should be 

made of the rate of burning of pieces of the fuse whenever there is 

any doubt whatever as to its soundness. Although the manufacturers may produce a fuse with a regular rate of

* burning, the rate may be changed by bad handling,

as, for instance, by squeezing ths fuse so as to disturb 

the powder core, or by suddenly and roughly opening the coil when 

it is stiff from cold, so as to crack the fuse; or the fuse may be injured

by rubbing' against the rough surfaces of the rock. 

fuse"6 ln cuttlne In cutting the fuse and in fitting it into place, care

must be taken that the powder core does not run 

out from the fuse, for that might cause a misfire.

Detonators (which are also called blasting caps, and sometimes are

called exploders, though the last term applies to any

Detonators. £ ' . ° LL

means or producing an explosion, and therefore is 

not commended here) consist of copper capsules about as thick as an 

ordinary lead pencil, which are commonly charged with dry mercury 

fulminate or with a mixture of dry mercury fulminate and potassium 

chlorate that is compressed in the bottom of the capsule, filling it 

to about one-third of its length.

Dynamite and other detonating explosives are in practice fired by

means of detonators, for though they may be exploded

* ^7 the aid of squibs or fuse, or by means of gunpowder primers, yet the explosion so produced is not 

a complete one; the explosives are not used to their best advantage; 

all of the work that they can do is not done; and, moreover, the 

gases that are produced are usually dangerous. Where high explosives are employed, it is safer to fire with detonators strong enough 

to cause their most complete explosion. Permissible explosives should 

be fired by detonators, and are best fired by electric detonators of 

the strength prescribed for each one. (See p. 61.)
32 A PRIMER ON EXPLOSIVES FOR COAL MINERS.

Several grades of these blasting caps or detonators are to be found 

in the market, and they are differently designated by 

different manufacturers. The "strengths" of the 

detonators most commonly used, as measured by the

weights of the fulminating composition contained in them, are as

follows:

Grades of detonators and weight of their charges.

Testing-station grades. .

No. 3 ...................................................

No. 4...................................................

No. 5. .................................................

No. 6...................................................

No. 7.................................:.....,...........

No. 8...................................................

Commercial grades.

7X, or No. 20..........

8X, or No. 30..........

Weight of 

charge in 

grams.

0.54

0.65

0.80

1.00

1.50

2.00

Weight of 

charge in 

grains.

8.3

10.0

12.3

15.4

23.1

30.9

Detonators are fired by the aid of a piece of fuse. The end of the 

fuse is inserted in the mouth of the blasting cap and 

carefully pushed down until it gently touches the 

surface of the detonating composition, and then the 

cap is crimpe'd ontQ the fuse. (See PI. VIII, A.} The cap, with 

the attached fuse, is inserted in the charge to be fired, which, when 

placed in the bore hole and tamped, is ready for firing. The end 

of the fuse is lighted, and the fire burns'down the powder core until 

it streams against the detonating composition, which then detonates 

and causes the detonation of the explosive with which it is in contact. 

It has been found at the Pittsburg testing station that the flame 

which rushes out from a fuse when it is ignited at 

tne mouth of a bore hole will ignite an explosive 

mixture of mine gas and air. Therefore fuse should 

not be used, either alone or with detonators, in fiery mines.

The .practice of fitting the fuse to the detonator is common in

quarries, tunnels, and mines that are not gaseous.

Fuse and detona- Accordingly, it is customary to make both detonators

tors must be of & J. ' . J

standard size. and ruses in standard sizes, so that the ruse may 

easily slip down within the mouth of the detonator 

and yet make a neat fit within it.

By the use of'electric detonators (also called electric fuses), the 

dangers that are common in the use of squibs or fuse 

in gaseous coal mines are avoided. (See PL VIII, B, 

and fig. 3.) These electric detonators are simply 

ordinary detonators that have been fitted with a means of firing them 

by the electric current. This is done by inserting within them two 

copper wires, joined at the inner ends by an extremely fine platinum 

or other high-resistance wire, which, like the carbon filament in the 

ordinary incandescent lamp, becomes heated till it glows when an

Electric detonators.
U. S. GEOLOGICAL SURVEY

A. CRIMPING DETONATOR ON FUSE.

B. DETONATORS AND ELECTRIC DETONATORS.
SQUIBS, FUSE, AND DETONATORS. 33

electric current is passed through it. This wire, known as the bridge, 

is placed above the detonating composition, and is surrounded by 

gun cotton or loose fulminate. The space above it and the rnouth of 

the capsule are then filled and closed by means of a plug of sulphur or 

other waterproof composition, which is poured in while soft. The 

copper wires pass through the plug and are long enough to extend outside the capsule. These outer ends are called the legs or wires of the 

electric detonator. Although the copper wires are bare within the 

electric detonator, the legs outside are covered with an insulating 

wrapping. These legs are made of different lengths 

in order to suit different depths of bore holes. The 

charge of detonating composition differs in the different grades of electric detonators so 

as to give different strengths. 

The following table gives the grade

and weight of charge for the more 

common electric detonators:

Grades of electric 

detonators.

Grades and weights of charge of electric detonators. Sulphur 

filling

Testing-station 

grades. .

No. 5.. ..........

No. (I............

No. 7. ...........

No. 8............

Commercial grades.

Weight 

of charge 

in grams.

' 0.80

1.00

1.50

2.00

Weight 

of charge 

in grains.

12.3

15.4

23.1

30.9 Gun cotton or __ 

mercury fulminate 

(loos'e)

In loading

FIGURE 3. Electric detonator, showing 

its component parts.

bore holes electric detonators are placed in the 

Firing eiectnc de- charge'lust as detotonators. i c

nators with ruse are, and 

the bore holes are tamped in a similar 

manner. To fire the charge, the legs of 

the detonator are connected by leading 

wires to an electric device at a safe distance, and from it the current 

is sent to fire the blast. No flame can escape from the bore hole 

during the firing, for the tamping fills the hole completely, and 

hence blasting in gaseous mines is made much safer.

Only electric detonators are used at the Pittsburg testing station 

in the tests of explosives for use in mines.

What are called delay-action electric "exploders" or detonators 

are now being offered for use where a number of

trte deto^o0 160" h°leS al>6 t0 be fired at OnC6 > but SO that the charges

may explode one after another. This is done by 

placing a piece of fuse or other device in the electric detonator

16210 Bull. 423 09 3
34 A PEIMER ON EXPLOSIVES FOE COAL MINERS.

between the detonating composition and the bridge and inclosing 

the whole so that the flame may not escape from the blast hole. In 

the present state of knowledge this practice is not commended for 

use in coal mines.

In the description of mercury fulminate attention was called to

its extreme sensitiveness to heat, friction, or blows 

detonators11 * ** an<^ *° ^e extreme violence of the explosion which it

undergoes. All these properties therefore belong to 

detonators and electric detonators, and these little devices should 

be treated with the utmost respect. Never attempt to pick out any 

of the composition. Do not drop them or strike them violently 

against any hard body. Do not lay them on the ground where they 

may be stepped on. Do not step on them. In crimping, take the 

greatest care not to squeeze the composition, and never crimp with 

the teeth, for there is enough composition in one of these small capsules to blow a man's head open. They should be stored in a dry 

place and in a building apart from any other explosives. They 

should never be carried into a mine with other explosives, and they 

should never be placed in a mine near other explosives except in 

bore holes. When carried or shipped they should be packed firmly 

with a quantity of elastic material, such as felt or the coiled legs of 

the electric detonators, about them, and they should not be exposed 

to heat, blows, or shocks of any kind. 

MINING COAL WITH EXPLOSIVES.

No universal rule can be made for blasting coal, for the local

conditions, the character of the seam, and the method

mines.dltl°ns in C°ai °^ working make it necessary to use different means

in different mines and sometimes even in different

parts of the same mine. The best method of blasting in any given

mine or part of a mine is determined by practical experience and

observation.

The placing of bore holes, as well as the size of the charge, is of 

vital importance. In placing them special attention and due consideration should be given to the bedding and cleavage planes in the 

seam; also to slate and bone parting, horsebacks, clay slips, and other 

local irregularities.

In this country, apart from the not widely used long-wall system 

and the pillar pulling or withdrawing, in both of 

soUd°0tinS °fl thC which little or no explosive is used, there are two 

general methods of bringing down coal in entry driving or room work, namely, "shooting off the solid" and undercutting 

or shearing before shooting.

In the coal mines of the middle interior fields, where shooting off 

the solid is largely practiced and where there are no marked faces or
MINING COAL WITH EXPLOSIVES. 35

Need of slow-actIng explosives.

butts, the following method is used: A hole is bored or drilled in the 

fac.e at or near the middle of the seam, at such a slant as to make a 

small angle with the face. If an imaginary line (AB in fig. 4) drawn 

from the back of the drill hole at right angles to the hole passes out 

of the open face, and if that distance is not too great, the hole is 

rated as "safe" by those who use the method. If, however, the 

hole extends beyond A to X (fig. 4), the extended part is said to 

be "dead" and the hole is considered "unsafe." A hole is also considered "unsafe" if the angle ACB is greater than 35°. In the softer 

coals and where the joints or cleavage planes (cleat) are favorable a 

greater angle is used, but no drill hole, even under such favorable 

conditions, is bored at an angle greater than 45°.

In shooting off the solid only one face of the coal to be thrown 

off is exposed. It must be torn off along the line AB 

and AC (fig. 4) and in addition must be forced out 

along

the bedding planes at £ 

top and bottom. Where 

such bedding planes 

are smooth this is not 

difficult, but generally 

they are irregular, and 

a strong shearing force 

must be exerted parallel to the bedding 

planes, both at the top 

and bottom. This 

method to be effective 

requires a slow-acting

explosive, and black blasting powder has been much used in the work. 

A second hole and even a third one is sometimes drilled and 

charged before the first one is fired, and these are called 

"dependent" shots. The fuses are sometimes made 

of different lengths and lighted at the same time, with the expectation that the shots will go off in the proper order. Such practice is 

now generally held to be very wrong even in "solid shooting" districts. The second and third holes should not be drilled until after 

the first shot has been made, so that the location of each shot can be 

properly judged.

The size or weight of the charge in shooting off the solid varies 

much in different coals. In fact, it is extremely difficult, even in the same coal, to judge the amount 

correctly each time. If undercharged, the hole is likely to "blow 

out;" hence it follows that holes are almost invariably overcharged, 

and in some districts all sense of right proportion has been lost by 

the miners.

FIGURE 4. Shooting off the solid.

Dependent shots.

Overcharging.
36 A PRIMER ON EXPLOSIVES ,FOR COAL MINERS.

Aside from the dangers in the use of black powder, the uncertainties 

in proportioning the charge to the work are such that the method of 

shooting off the solid can not be approved as either precise or safe. 

Many of the great mine disasters of this country have undoubtedly 

started from misjudged or overcharged shots off the solid.

The other method of bringing down the coal, in which the explosive 

is assisted by undercutting or shearing beforehand and 

"* which was early used in this country, is now being 

readopted in most parts of the country. The object 

of undercutting or shearing is to expose two faces of the mass of the 

coal to be brought down, and, as coal generally tends to break 

along vertical planes, to permit the explosive to exert a wedging 

effect, rather than to shear or tear off the mass as it must in shooting off the solid.

There are two ways of applying this method shearing and undercutting. Occasionally, where the coal is hard to shoot down, both

shearing and undercutting are done, so that a 

less amount of explosive is needed; in fact, 

in some places none is 

required, as the coal 

can be wedged down.

Where the cutting is 

by hand and the top and 

bottom part "freely," 

shearing is the easier, 

and is usually employed 

in entry or narrow 

work. In some cases

FIGURE 5. Shearing.

Shearing.

the shear or vertical cut is made on but one rib, but generally it is 

made in. the center of the narrow face and the shot is so placed as to 

throw the coal toward the shear.

Where the coal is all alike in character and parts equally well at 

top and bottom the hole is started at or near the middle of the seam and drilled nearly parallel with the 

shearing, slanting a little upward to cross the bedding planes, and 

also to clear itself of dust as it is being drilled. The hole should never 

go deeper than the cutting, and it is better for it not to go as deep by 

at least 6 inches as the cutting. In figure 5 the back of the bore hole 

is shown as reaching the projected line of the rib, b.ut in softer coals 

the backs of the bore holes are usually at least 6 inches from the 

projected line of the rib.

In districts where black powder is still used it is conceded that a 

shot hole of this character should never be charged with more than
MINING COAL WITH EXPLOSIVES. 37

Charge of explosive In shearing.

Roof

2 pounds of/black powder, and better with much less. It is difficult 

to make rules for an exact amount, because the 

proper amount differs with the length of the hole and 

cutting, the strength of the coal, and the way that it 

parts from top and bottom. However, the work should never be so 

laid out that it will require more than 2 pounds of black powder. If 

one of the permissible explosives is used, the charge should be, in 

general, only about one-half (by weight) what would be required if 

black powder were used; but no work should be so laid out that is, 

no drill hole should be so located with reference to the shearing as 

to require more than a pound and a half of the explosive.

Where the place is so wide that another hole is required near the 

 first, when the first has done its work properly a similar situation is 

left for the second hole. 

Where the coal is undercut,

either by hand or machine, the 

purpose of the

Undercutting. , . .

shot is to bring

down the mass of coal by wedging from above. In such a 

place the greater part of the 

force of the explosive used in 

the first shot will go to shear 

off the coal on both sides of 

the shot, the expanding gases 

from the explosive working 

along the bedding plane at the 

line of the drill hole and the 

mass pivoting at the back 

the bedding; of the coalFloor 

FIGURE 6. Snubbing shot.

of the undercutting. The stronger 

that is, the less marked the vertical 

lines the more difficult is this shearing, which then becomes a 

tearing, rending effect at the 'sides of the mass, so that the shape 

of the mass is somewhat conical, the top being at the line of the drill 

hole and the base at the undercutting. Under the circumstances 

the coal above the drill hole generally does not come down, but it is 

usually so shattered that it may be pulled down with 

a pick. Necessarily this first shot takes more explosive than later shots, but the amount should never 

be more than that already stated for the shearing method.

To help the first or "buster" shot, if the undercutting has been 

done by machine, it is advisable, and in some cases 

of the necessary, that the coal at the front edge of the undercutting be "snubbed" off either by the pick or by 

a small "pop" or "snubbing" shot (fig. 6). In narrow work, if the

Charge 

cutting.

Placing 

shots.

under"
38 A PEIMER ON EXPLOSIVES FOE COAL MINERS.

" buster" shot has done its work properly at one rib, the second shot 

is placed at the other rib. In wider work the "buster" shot is usually placed near the center of the room face and the second and third 

shots are placed on either side (fig. 7). Each of these is so placed as 

to throw down a mass of coal which practically has three faces free 

the front, the bottom, and one end. The chief work of the shot is to 

wedge off the rib end and push away from the back/- Such a shot 

usually only requires from one-half to three-quarters of a pound of 

one of the permissible explosives. The work should be adjusted to 

these charges, so that if three shots besides the snubbing shot (if one 

is needed) are not enough, four or even five shots 

snouW be used. It is far safer to use a number of 

' shots with a small amount of explosives in each than 

to use a few shots with a larger amount; and on the whole less explosive will be needed in all the small shots than in the few large shots.

Roof

s^tu Barges e ° ° f

Floor 

FIGURE 7. First or "buster" shot.

cutting °

The depth of the undercutting varies with the character of the coal 

and with the thickness of the seam, but in hand-pick

work the depth is not commonly greater than the 

thickness of the seam. Where machines are used to 

undercut, the depth is from 6 to 7 feet, depending on the machine. 

With machines the cutting is usually done at the bottom of the seam; 

if the seam is thin (less than 3 feet) the cutting is done in the underlying clay, if there is any. Where the undercutting is done by hand 

pick, it is sometimes done in a soft layer near the middle of the seam, 

or in a parting of soft clay, but so far as the placing of the shots is 

concerned, the part above such an undercutting may be regarded as a 

thin seam, the coal below the cutting being lifted afterward by 

"heaving" shots. Generally the cutting is in the bottom, and where 

it is so the shots are usually placed above the middle of the coal and 

sometimes near the top. Where the coal is undercut and black 

blasting powder is used, owing to the powder's slow wedging action the 

exact position of the shot is not of such special importance as it is 

where permissible explosives are used. As already explained, these
 MINING COAL WITH EXPLOSIVES. 39

are quicker in action than black blasting powder, and unless they dislodge the coal instantly their force is spent in shattering the coal near 

the drill hole. Therefore with permissible explosives the mouth and 

back of the drill hole should be nearer the roof and the hole should 

slant upward in order that the back of the drill hole may reach the 

top bedding plane (fig. 8), The break will then be clean and a 

wedging action will be exerted along the top bedding plane.

In' the use of permissible explosives, special care should be taken 

that each bore hole has the same width throughout 

anc^ is w^e enough to permit the cartridges to pass 

through it without too hard ramming. Too small a 

hole may cause the cartridge to stick, and nitroglycerin explosives or 

even black powder may be exploded by the friction of the tamping 

bar against the sides of the hole. Daily attention should be given to 

the drills that are used in

drilling the bore holes, and

the points of the bits when _ 

being sharpened should be 

made to a standard size. 

Before a shot is fired in 

a working

Dust must be wet i nn «u ,^; > 

down and removed. PlaCe bug

dust and all

other coal dust should be Coal 

thoroughly wet and sent out 

of the working place. No 

cause of explosions has been 

more common than the 

presence of coal dust when 

shots are being fired. If the

WOrkillg place is naturally FIGURE 8.-Bore hole for permissible explosives.

dry, it should be thoroughly sprinkled, and all the ribs, roof, and props within 40 feet of

the shot washed down by hose before shots are fired.

Good results have been obtained in bituminous coal mines during

the winter months by warming and moistening the 

mine's m * d * f y l n e air entering the mine by means of exhaust steam and

spraying devices. In experiments made in December, 

1908, at the Pittsburg testing station the outside air entering the 

gallery was warmed up to a mine temperature and moistened by 

drawing it through humidifiers. It was found that if the air. is kept 

at a relative humidity of 90 per cent and a temperature of 60° F. for 

forty-eight hours, thus giving conditions like those of summer in a 

mine, the taking up of moisture by the dust and the blanketing effect 

of the moist air prevent a general. ignition of the dust by a blown-out 

shot of black powder.
40 A PRIMER ON EXPLOSIVES FOR COAL t

Since the new permissible explosives began to be used it has been

shot flrers f ound that more satisfactory results are obtained in 

mines where the loading and tamping of all shots are 

done by a few competent men known as "shot firers/'

For the greatest safety the loading and firing of all shots should 

be done by shot firers.after all other men have left the mine. The 

practice of having all shots loaded and fired by shot firers during 

the shift, which has lately been introduced in some of the mines of 

the Pittsburg district, is certainly a step in the right direction.

It is plain that the greatest safety and best work can not be obtained when the miners are allowed to load and fire their shots, 

because the new permissible explosives must be properly handled 

to get the desired results.' The shot firers should be selected from 

the more intelligent miners, and they should be thoroughly instructed 

in the great dangers that arise when the permissible explosives are 

used in any other'manner than that specified by the Pittsburg testing station.

LOADING AND FIRING CHARGES OF EXPLOSIVES.

In blasting, any explosive gives the greatest disruptive effect 

when the charge most completely fills the bore hole 

holes a n§ ° re from, side to side. If the explosives are supplied 

in cartridge form this condition can often be obtained 

in the bore hole by splitting the wrapper, gently pushing a cartridge down into place in the bore hole with a tamping stick, gently

5 Inches

FIGURE 9. Bore hole ready for firing.

squeezing it so that it spreads out to fill the entire width of the hole,

and repeating this with each cartridge until the charge has all been

put in. Finally, the detonator is placed oin the last cartridge put

_ . in, and this cartridge is known as the primer. The Primer. ° * 

primer is gently pushed down into place in firm contact with the remainder of the charge, arid the hole is tamped (fig. 9). 

If the same weights of different explosives are of equal strength, the 

one that takes up least space that is. the densest Density of charge. .-. . . ,

will nave the greatest effect in breaking coal or 

rock. Of two cartridges of equal size containing different explosives the heavier cartridge is said to have the greater density.
AND FIRING CHARGES OF EXPLOSIVES. 41

Black blasting powder to be used in blasting is made up into a 

cartridge by means of a paper wrapper which has 

been formed about the handle of a pick. When this 

cartridge has been charged with powder, the electric 

igniter or fuse is placed and well fastened, and the. cartridge should 

then be gently pushed down into the bore hole by means of a 

wooden tamping stick, which is safer than any metal

Tamping stick. A I l> i, u u i

bar. 'An iron tamping bar should never be used. 

When squibs are used, the cartridge of powder is placed in the 

bore hole and then the tamping is put in about a copper or brass 

needle rod until the hole is filled. Then the copper needle is withdrawn and the squib is put through the opening. 

When only fuse is used, it should be long enough to reach beyond

the mouth of the bore hole. The tamping should be

tal1 * fuse and Packed in about the fuse quite to the mouth of the

bore hole, and the fuse should be completely surrounded by tamping.

It is observed that in some mines the practice has been to use 

but a short length of fuse and to let the charge 

explode untamped, or simply secured by running 

the tamping bar into the hole. This is a very bad 

and dangerous practice and should be forbidden. 

When detonators are used together with a fuse, the fuse should 

be cut off squarely at the end, gently inserted within 

the detonator until the powder core touches the detonating composition, and then, with the fuse held in 

the left hand, the detonator should be crimped onto the fuse with 

crimpers close to the open end of the cap, so as to make a perfectly 

tight and secure joint, care being taken in crimping that no pressure 

is brought to bear upon the detonating composition.

Two ways are in use of inserting the detonator and attached fuse 

into the stick of explosive that goes on top of the 

charge and is known as the primer. The more 

approved way is to open the top of the cartridge or 

stick of explosive by unfolding the paper at the end; then to make 

a hole by means of a wooden skewer or lead pencil in the top of the 

cartridge, deep enough to let the detonator be pushed into it up to 

the line of crimping; then to gather the end of the paper jacket or 

envelope together about the fuse, the whole being bound with twine, 

so as to fasten the detonator and fuse firmly in place.

Another way that is sometimes used is to insert the wooden 

skewer into the side near the upper end of the priming cartridge so 

as to make a slanting hole in the charge, deep enough to take the 

detonator up to the crimping mark, then to insert the detonator and 

bind it and the fuse close to the cartridge with twine. (See PL IX, A.)
42 A PEIMEE ON EXPLOSIVES FOR COAL MINERS.

The first way is perhaps more generally used, and it is better 

where the cartridge fits neatly into the bore hole. 

Be careful not to When the second way is used, the bore hole must be 

of primer. larger, as there should be some leeway between the cartridge and the side of the hole. In either way, when 

the primer, with the detonator and fuse, is put into the bore hole, 

extreme care should be taken that they do not come apart, for if 

there is any space between the cartridges in a charge, or particularly 

between the detonator and the explosive in the priming cartridge, 

the explosion may be prevented altogether, or may 

Detonator must be a very poor one. Likewise, when a fuse and detonot be completely i i r 1,111,4.1 ±u *

buried. nator are used in loading, care should be taken that 

the detonator is not completely buried in the explosive, for as the fuse burns and fire rushes from its end some of it 

may blow out over the top of the detonator and set fire to the explosive about it before the detonator is set off. This has been a common 

cause of inferior and dangerous explosions.

The same sort of trouble happens if coal dust or any other dirt 

is allowed to get between the cartridges in a charge, 

r" or between the priming cartridge and the charge. 

In loading, extreme care should be taken to make sure 

that the cartridges all touch one another closely. 

When electric detonators are used they are fastened in the priming 

cartridge in ways like those described above for deeleCtri° tonators used with fuse. When the electric detonator is inserted in a hole in the side of the priming 

cartridge, the practice has sometimes been to fasten it firmly by 

taking a half hitch around the priming cartridge with the legs of the 

detonator, the loading and tamping being then done as already

described. This last means of attaching the electric detonator to 

the priming cartridge is not a good one, because the legs are likely to 

become kinked, and also because there is a chance that when the 

priming cartridge is pushed into place the insulation may be rubbed 

off from the legs and the wires may be short-circuited.

Although it has been stated that with certain explosives, which 

are somewhat largely used, the cartridge case may 

sv\ t and1 "tightly ^e SP^ anc^ *ne charge rammed firmly into place, 

packed, may not ex- this is not the universal practice and should not be 

plode' done with all the ammonium-nitrate class of explosives (p. 21), nor with some of the nitro-substitution explosives, for if 

they are tightly rammed in the bore hole, it is difficult or even almost 

impossible to explode them.

After the priming charge with its fuse and detonator or its electric 

detonator has been inserted in the bore hole, the hole should be
LOADING AND FIRING CHARGES OF EXPLOSIVES. 43

Instructions for 

tamping.

tamped with clay or with other material that can not burn. It 

should never be tamped with coal dust (either wet or 

dry) or with machine cuttings, known as "bug dust." 

The tamping should be done by means of a wooden 

tamping stick. The pressure in tamping should be very gentle on 

the first tamping material put in, particularly if detonators are used 

in the primers, and great care should be taken at this time not to 

disturb the position of the detonator in the primer. Special care 

should be taken not to draw the detonator out from the primer or 

the fuse out from the detonator. When fuse is used, care should 

also be taken not to rub the surface off of it.

After the first 6 inches of the tamping material has been pressed 

down, greater force may be used in ramming the rest, because the 

firmer the tamping is the better is the work of the explosive and the 

less is the chance of a blown-out shot. The tamping should be continued quite up to the mouth of the bore hole. If fuse has been 

used, the upper side of it near the end may now be cut into on a slant, 

with a sharp knife, and the outer part bent away so as to form a

FIGURE 10. Loaded bore hole showing air space about the charge.

notch in which the powder from the core gathers and to which the 

. igniter is applied. This cutting prevents the loss of powder from 

the fuse and makes it easier to light.

The shattering effect of high explosives may be lessened in loading 

simply by pushing the cartridges into place without

Air spacing of splitting or afterward squeezing them, so that an air charge to reduce * ° ^ ° ;

shattering effect, space will be lelt about the cartridges in the bore hole, 

and then proceeding with the priming and tamping. 

This air space notably lessens the shattering effect of the explosive 

(fig. 10).

Where it is desired to use black blasting powder, electric blackpowder igniters, sometimes called electric safety fuses 

or squibs, are recommended for setting off shots. 

They are made in a general way like electric detonators, but gunpowder or other slow-burning composition is used in them instead, 

of detonating composition. They are much safer for use in coal 

mines than ordinary squibs or fuse, both because they do not throw 

fire into the mine air and because they permit better tamping of the 

bore holes.

Electric Igniter.
44 A iPRlMER. ON EXPLOSIVES FOR COAL MINERS.

It sometimes happens that it is desired to fire a number of charges 

at the same instant. This is readily done, with electric detonators 

by coupling them up in series from hole to hole and firing by one 

discharge from the machine. This method endangers the roof and

may cause falls. In mines other than coal mines it 

fu** stantaiieous may be done by instantaneous fuse running from a

central fuse t6 the several charges, but this practice 

is not.a good one in coal mines, because the fuse may set fire to the 

dust .or gas that is present.

In coal mines it is more commonly desired to fire one or more of

the charges before the other charges, and this may 

omitOTs"a0tl011 det" be done in a single act of firing by the use. of the

delay-action electric detonators already described 

(p. 33). An ordinary electric detonator is placed in the charge 

for the central breaking-down shot, and delay-action electric detonators are placed in the charges for the right and left rib shots. This 

method of firing has many advantages over the methods of firing 

successive shots by means of different lengths of running fuse, but 

neither method is recommended for use in gassy or dusty coal mines. 

The safest way is to fire but one shot at a time, and to allow time

enough between shots for the ventilating current

safety m single to m±K with and render harmless the products of

shots Time between ,

them. combustion rrom the previous shot 'and to carry 

off any coal dust that may have been thrown into 

the air by the shock of the previous shot. The interval of time that 

should elapse between shots differs with local conditions and the 

amount of ventilation, but in ordinary mining practice the interval 

should never be less than five minutes for shots made in the same 

working place.

In the making up of charges for loading bore holes and during 

the loading, extreme care should be taken that the 

expl°sives are not exposed to the flames from naked 

lamps or to sparks from the striking of metals upon 

each other or upon rocks, or from any source, since any of these 

may cause serious accidents.

As already suggested, the right size for a charge of explosive for

blasting in a coal mine can be found better by practice

Failure of formu- than by theory. Several formulas have been devised

las for size of . '*; . . , , charges. by which to determine the right charge beforehand, 

but unfortunately they have not given satisfactory 

results in practice. If the material or mass to be blasted were always 

alike throughout, and of equal hardness, theoretical rules could be 

made to apply, but such is not the fact. Differences in the resistance of the material to be blasted and in the rate of burning or 

detonation and the breaking force of the different explosives all 

affect the results of a blast.
LOADING AND FIRING CHARGES OF EXPLOSIVES. 45

Thus, for instance, in soft bituminous coal a permissible explosive

containing only 20 per cent of nitroglycerin has

comparison of ef- \)Qen found to bring down more coal, and better

fects of different ex- - , ,

plosives. coal, than one made under a similar formula but 

containing 25 per cent of nitroglycerin. A very 

quick explosive should not be used in bituminous coal mines where 

lump coal is sought. For instance, 40 per cent dynamite, which 

has been lound by experiment at the Pittsburg testing station to 

have a rate of detonation of 4,688 meters (15,380 feet) per second 

is unsuitable for producing lump coal; but the permissible explosives 

that have rates of detonation between 1,866 and 3,617 meters 

(6,122 and 11,867 feet) per second are found to be well adapted 

for this work. Explosives that develop very high pressures are 

also unsuited for this work. Thus the 40 per cent dynamite referred

to above has been found to produce a pressure of 8,308 kilograms

per square centimeter (118,165 pounds per square inch), but the

permissible explosives show pressures as low as 4,833 kilograms per

square centimeter (68,740 pounds per square inch).

In deciding on the charge of a permissible explosive for use in

a coal mine it is safe practice to use about one-half

size of charge of the weight of black blasting powder that would be

sives for coai mines, needed to do the work; but no charge of permissible

explosives should be more than \\ pounds. As stated

before (p. 39), bore holes for permissible explosives are placed by a

different rule for depth and direction than that which is followed

when black powder is used. No permissible explosives nor any

high explosive should ever be used in the same bore hole with black

blasting powder.

The most obvious objections to overloading are that it crushes 

and wastes the coal, and that it throws fire and flame 

*° ou^ m^° *ne au: °^ the mme. Another objection 

is that the surplus force of the shot may so weaken 

the roof and surroundings as to cause falls, which may not occur, 

however, for some time after the shot has been fired.

Underloading, on the other hand, not only causes loss and waste, 

but it may so fissure the coal near by as to make it 

underloading. 118 *° dangerous to fire another shot near the place. At 

. the same time it may happen that the underloaded 

charge, though not strong enough to bring down the coal, may spring 

the bore hole, throw out the tamping, and give a blown-out shot; 

that is, a charge that is not heavy enough to make a blast may be 

heavy enough to act in a bore hole as it would in the barrel of a gun; 

and this may happen particularly if the tamping' is not well secured 

and firm. Blown-out shots are especially to be feared in dusty and 

gassy mines, because it has been found that explosive mixtures, such
46 A PEIMEB ON EXPLOSIVES FOE COAL MINERS.

as are present in such mines, are most sure to catch fire and burn 

most completely when a mass of flame, and more particularly a mass 

of glowing solid particles, is thrown into their midst. Investigation 

has shown that the larger number of the recent disasters in coal mines 

have been due to blown-out shots.

Premature explosions, misfires, and hang fires are most likely

to happen when squibs and fuses are used to set

premature expio- Off charges, owing to defects that may be in them

sions, misfires, and & ' & . J

hang ares. from the first, or may be caused in the handling, 

carrying, or loading of them. Miners are especially

warned in case of a hang fire to avoid returning to the breast until 

half an hour has passed. Hang fires rarely hapPartial explosions.

Keep away from a pen w^n electric detonators, but it is possible that

hang fire for half an fl ' r

hour. they may happen more often with delay-action

detonators.

Incomplete explosions may result from several causes. They may 

be due to failure to push in all the cartridges of a 

charge till they touch one another, thus leaving an 

air space between them, or else a mass of coal dust 

or dirt, which breaks the path of the detonation from cartridge to 

cartridge. They may be due to the pulling out, even but a little 

way, of the detonator from the primer or of the fuse from the detonator. In the use of nitrate of ammonia or nitro-substitution 

powders, incomplete explosions may be due to too tight packing 

and compressing in the bore hole. In any case, a partial explosion 

is a marked source of danger; first, because it may have the effects 

of an underloaded charge; second, because the unexploded part of 

the charge may burn and throw out flame and sparks into the mine, 

and also give out poisonous gases and fumes; third, because the 

unexploded part of the charge, if it is not burned up, may be 

brought down with the coal and give rise to an accident in the 

breaker, or, if it passes the breaker, to an accident in the transportation or the use of the. coal. Whenever there is a partial explosion, if 

coal has been brought down, careful search should be made in the 

coal for the remainder of the charge.

In case of a misfire no attempt should be made to draw the charge, 

but a new bore hole should be placed at least 2 feet away from the 

first one and fired, and after the coal has been brought down it 

should be carefully looked over to find any unexploded material that 

may have come from the hole that misfired. When a hole charged 

with black blasting powder has misfired the tamping and charge may 

be withdrawn, drenching them with water while withdrawing them. 

After the hole has been dried out it may be reloaded.
FIRING BLASTS BY ELECTRICITY. 47

FIRING BLASTS BY ELECTRICITY.

The methods used in causing the explosion of charges in blasting 

depend on the nature of the explosive. To cause the 

by&&me °* ^^ explosion of an explosive of the black-powder class, 

it is only necessary to put a flame to it, but a violent 

shock is necessary to cause the detonation of high explosives so that 

they will have their greatest breaking effect. As already stated, 

black-powder charges are set off by means of squibs, fuse, or electric 

igniters. Squibs and fuse are set on fire by means of the flame of 

the miner's lamp, or sometimes by heating a wire to the glowing 

point in the miner's lamp and applying it to the match of the squib 

or the cut end of the running fuse; but evidently these methods 

would be dangerous in fiery coal mines, and hence they should never 

be used in such mines.

An electric igniter or an electric detonator should be so loaded 

into a bore hole that while it is in perfect contact with the charge the 

legs of it reach at least 6 inches out of the completely tamped hole. 

Both legs should be bared of their insulation for about 2 inches from 

their ends, and the wires scraped bright so that a good 

electrical contact can be made with them. Each leg 

is then firmly connected with one of the leading wires 

by about five turns. It is bad practice to have the two splices directly 

opposite each other, because when the leading wires 

splices should not are pulled the splices may touch one another and

be opposite- Wrap- * i , , i i -n j. j.i ping splices. thus make a short circuit, which will prevent the 

electric igniter or electric detonator from being exploded. A better plan is to wrap the bare wire splices with tape 

made for the purpose, which will completely insulate them.

After the legs are spliced to the leading wires (and only after), the

wires are connected to the firing machine from which

connecting lead- the electric current is to be obtained. This last con- ing wires to firing . machine. nection should never be made until all the men are 

at a safe distance from the place where the blast is

to be fired. The rule should be made and never broken that when bore 

holes are charged the connecting up shall move from

be made from bore the bore hole back to the firing machine. The work

hole to firing ma- m ^ne mine should be so organized that it can never

be possible for the leading wires to be coupled up to

the firing machine while anyone is about the place where the holes

are being charged and where the blast is to be fired. In heavy blasts

in development work, two or more electric detonators may be used

to good advantage in the same bore hole. For this

na^oTs^ series*6*0" purpose they are connected up in series, which means,

for two detonators, that a leg of each is bared and

the two legs twisted together and wrapped witk insulating tape, and
48 A PEIMEE OST EXPLOSIVES FOE COAL MINEBS.

that then the two free legs are attached to the leading wires, just 

as where but a single detonator is used. In coal mining the charge 

used should never be so large as to require the use of more than 

one detonator in the same hole.

When it is desired to fire two or more holes at the same time the 

detonators for these holes should also be connected up

Connecting holes. . . . , * in series, and to bridge the space between the holes a 

cheap insulated wire, known as connecting wire, which is not as 

heavy as the leading wires, may be used. In coupling up a series of 

holes for this purpose, one leg of a detonator is connected to one leg 

of the detonator in the next hole, and so on to the last hole. There 

is then left one free leg in the first hole and one free leg in the last 

hole, and these are spliced to the leading wires. The usual precautions should be taken to wrap all the splices with insulating tape, so 

as to completely insulate them, and thereby insure a good circuit 

through which the current may pass. It should be borne in mind 

that the greater the number of holes to be fired in a single blast the

greater is the necessity for making sure that the cirDanger from a cu^ is complete throughout, because if there is a

break or short cir- r . .° ' .

cuit. break or a short circuit at any point, the blast will 

probably fail to fire. The delay, expense, and danger

caused by such a failure can be prevented by giving careful attention

in the first place to the charging and the wiring.

The electric current for use in firing electric igniters or electric 

detonators may be obtained either from primary batteries, such as dry-cell batteries, or from secondary batteries, such as storage batteries, or from electric-lighting circuits, or from

generators known as electric firing machines. (See PI. IX, 5.) 

Firing charges of explosives by means of ordinary dry cells has 

been prohibited in foreign countries, because premaDry cells. *\ . , & , . - \

ture firing or detonators, and sometimes or the charge, 

has been caused by the wires coming into contact with the poles of 

the batteries. Safety-contact dry-cell batteries have lately been 

introduced abroad and in this country. These are made with a 

spring-key contact, or with two safety-spring contact buttons, which 

are the poles of the battery. The two leading wires are laid on the 

buttons, which are at the same time pushed downward. When the 

pressure of the thumbs is released the contact is broken. If the 

wires of a detonator accidentally come into contact with the poles of 

the battery, the current can not be discharged unless both poles are 

pushed downward.

Dry cells, small batteries, and some firing machines can be carried 

about by the miner who is to act as shot firer, and this is an advantage,
U. S. GEOLOGICAL SURVEY

A. FUSE AND DETONATOR FITTED INTO PRIMER.

B. SECONDARY BATTERY, FIRING MACHINE, AND DRY CELL.

C. TESTING DETONATOR.
FIRING BLASTS BY ELECTRICITY. 49

that insures him against premature firing by any other person. 

Such small devices can at best be used with only a few 

shots in one circuit. The number of shots to be fired 

and the length of leading wires and other conductors through which 

the firing is to be done must be known beforehand, so that a battery 

of sufficient capacity can be selected. Batteries often fail to fire 

blasts because they can not send such a current as will fire through the 

great length of leading wires, connectors, and detonator legs that is 

used for the blast. A simple way to test the strength 

°^ ^o batteries is to pass the current through a small 

electric lamp of known capacity and note the brightness of the light given by the lamp. Another way is to pass the current from the battery through a testing circuit whose resistance is 

equal to that of the circuit of a blast and which has in it one electric

detonator. If the battery fires this detonator (which should be put

in a safe place) it is strong enough and in good condition. 

When the electric current for firing is obtained from an electriclighting circuit the connections are usually made in

Firing from elec- & & . ' . , / .

trie-lighting circuit, parallel; that is, one leg or every detonator is connected to one of the leading wires and all the other 

legs to the other leading wire. Care must be taken, by the use of 

insulating tape, that there shall be no short-circuiting 

connecting up in m these connections. This method has the advantage 

that if there is a defective electric igniter or electric 

detonator in the circuit its failure will not prevent the rest of the blast 

from being fired; but, on the_other hand, this method is objectionable 

because at any time after the explosion of the good igniters or detonators 

the unexploded charge with the defective igniter or detonator may be 

blown out and scattered in the coal, or it may even be set afire or perhaps exploded in the air of the mine by shock or friction. Furthermore, in this and other methods of electric firing an 

accidental premature blast may possibly be caused 

by leakage from the electric main to the earth and 

through the leading wires or connections, which may have become 

bared by rough handling or may not have been properly covered by 

the insulating tape. Premature explosions have been known to occur 

that were caused by leakage due to defective insulation.

Firing machines, sometimes called blasting machines, generate 

the electric current to be used in firing by mechanDynamo -electric jca| m^ng. A variety of such machines have been

machines. . , .

invented, but the two best-known classes are the 

dynamo-electric machines and the magnetos. The dynamo-electric 

machines are made like ordinary dynamos used for generating electric 

currents, differing only in that they are worked by hand. They contain a coil-wound armature which is rotated between the poles of an

 Bull. 423 09 4
.50 A PEIMEE ON EXPLOSIVES FOB COAL MINERS.

electromagnet. This armature can be made to revolve by means of 

a crank or a vertical ratchet geared direct to the spindle of the 

armature. The machines with ratchet bars are made so as to store 

up the current during a stroke, until just as the stroke is ended the 

entire current that has gathered is discharged through the leading 

wires.

These machines are built in different sizes and are rated according 

to the number of electric detonators they can fire 

Thus, a '"50-hoIe" machine will, when properly 

worked, fire 50 detonators at one discharge. The 

machines usually built for use in coal mines are rated as "4-hole" 

machines, and such a machine can be conveniently carried about by 

the miner or shot firer.

The magneto machines consist mainly of an armature revolving

between the poles of a set of permanent magnets.

They look much like the dynamo-electric machines

that are worked by cranks, and they are used in much the same way.

These magneto machines are used to a considerable extent in foreign

countries, but the "push down" dynamo-electric machine is the

one most commonly used in the United States.

The leading wires that carry the current from the blasting machine

to the blast hole are of insulated copper wire, copper

Leading wires. * '4.1, £ 4. J ?

being used because it is one or the best conductors 

of electricity known and has the further advantage of being but 

little corroded in damp mines. These leading wires or firing lines 

are insulated with a braided covering, which is better 

^ made :waterproof. In'some instances the two wires 

are twisted together and wrapped with an additional 

coating of braid, making them into one cable, which has the advantage of being more easily handled than two separate leading wires, 

and has also the advantage of the added protection given by the 

additional braiding.

After the blast has been fired, the ends of the leading wires should

be immediately disconnected from the posts of the

inspection and re- firmpr machine, and the lines should be examined

pair of leading wires , ° ; .

after firing. tor their whole length in order to see that the insulation has not been broken by coal or rock thrown 

against it, nor been stripped by the force of the blast. Where such 

defects or injuries are found, they should at once be repaired with 

insulating tape, and then the leading wires should be placed where 

they are not liable to injury until they are again needed.

For testing the line after it is connected up, and before the firing, 

in order to show that the circuit is complete and

Testing the line. . , . -11 that there is no leakage in the wires, a special galvanometer may be used, together with a battery such as many
SINKING SHAFTS AND BLASTING 'ROOK. 51

of the manufacturers of explosives now sell. This galvanometer, 

like others, bears upon its face a needle, which is turned or deflected if an electric current is present. By noting whether this 

needle is deflected or not one can tell whether the circuit is closed or 

open, and the extent of the deflection shows just how little resistance

there is in the circuit. To use the galvanometer, the 

eter!* "* BaJvanom" wires leading from it are connected to the two binding

posts of the firing machine, to which the wires leading 

to the charge have already been connected. The deflection may then 

be noted. The current generated by the very weak battery cell 

attached to the galvanometer should not be strong enough to fire the 

electric detonators used in the bore holes, but is enough to deflect the

galvanometer needle. This testing galvanometer,

w^n ^s attached "battery, should never be applied

directly to the face to be blasted, even when it is

being used to find out, when the test has shown no current, which of 

the electric igniters or electric detonators, are defective. The tests 

for the separate detonators or igniters should always be made through 

leading wires long enough to let the person making the test stand 

where he would be perfectly safe if the blast should be fixed; and on 

no account should this testing of the igniters or detonators be made 

while any person is so near that he may be in danger from the 

blast. (See PL IX, G.}

EXPLOSIVES IN SINKING SHAFTS AND BLASTING 

BOCK AND DIRT.

The use of any explosives other than permissible explosives is 

not recommended in any coal mine or part of a coal 

mine except in early development work, such as shaft 

sinking or entry driving through rock strata. In such 

work all men should be out of the shaft or working place when shots 

are fired.

After the coal has been reached and it has become necessary that 

shots shall be fired while men are in the mine, permissible explosives 

only should be used. After a mine has been.opened up, if rock or 

dirt is encountered, which may happen because of a fault or some 

other cause, it is quite necessary that permissible explosives be used, 

for it is known that inflammable gas is likely to be found in such 

places.

In the sinking of shafts or in the removal of rock or dirt by means 

of explosives, the methods to be followed in loading, 

> tamPlnS> tamping, and firing the charges of explosives are 

similar to those -described for use in blasting coal. 

In this, as in other work, electric firing will be found to be the safest 

means of shot firing, and in the long run the cheapest.
52 A PRIMER ON EXPLOSIVES FOR COAL MINERS.

It is not uncommon to hear the statement that high explosives, because they are quicker in action than low 

explosives, need not be tamped. This is a serious 

error. The fallacy of it has been repeatedly proved 

in the tests of many different explosives made at the Pittsburg testing 

station. It has there been clearly shown that the highest pressure 

an explosive can give, and therefore the greatest amount of energy 

it can set free, will be developed only when the explosive is confined 

in the smallest possible space. Hence after the charges have been 

loaded into the bore holes they should be tamped with such materials 

(the best being damp clay) as confine the charges most closely, and 

this material should be rammed in firmly, with the precautions 

already set forth, quite to the mouth of the bore hole.

In the appendix setting forth the test requirements for permissible 

explosives (p. 61) it is stated that electric or other 

detonators containing not less than 1 gram of the 

fulminating composition should be used in firing the 

charges. For use with high explosives in rock blasting, detonators 

of that strength are also best. Under no circumstances should an 

electric or other detonator be used of less strength than No. 5, containing 0.8 gram of the fulminating composition. The greater efficiency and certainty of the stronger detonator more than make up 

for its slightly greater cost.

In the sinking of shafts, after the soil has been removed and the 

overlying layers of shale and rock are uncovered, it becomes necessary 

to use explosives; and because in such a place the ventilation is 

always poor and the miner must wait for the fumes and smoke to 

clear away after each blast before he can safely return to his work, 

time can usually be saved by firing shots in groups

gr!uPnss sh°ts ln instead of singly. Dynamite, or, when the shaft is 

wet, gelatin dynamite, may be used for these shots, 

which should always be fired after the men are out of the shaft. The 

most economical and safest way of firing a number of shots at one 

time is by means of the electric current, with electric detonators. 

The older method of firing by fuse is dangerous and wasteful. Where 

fuse is used, there is always danger that a seeming misfire may 

prove to be a hang fire that is, the smoldering fuse may cause the 

charge to explode unexpectedly. Also, if by any chance there is 

any irregularity in the burning of the fuse, the miner can not 

properly judge the time necessary to get out of the shaft and out of 

danger after having lighted the fuse.

In shafts that run through rock, as most shafts do, there is no 

objection to the shattering effect of firing several 

stmuitane- s^o^s ^ fae same instant, and this method is

recommended; but when it happens that in shaft 

sinking the shattering effect would be harmful, and successive
SINKING SHAFTS AND BLASTING BOOK. 53

shots are therefore to be used, it is still advised that they be fired 

by electricity. For such shots, however, a less violent explosive 

may be employed, and the delay-action electric detonator already 

described (p. 33) may be used to good advantage.

The following explosives may be recommended, in a general way, 

for use when the size and condition of the material resulting from the 

blast; is not important, for example, in the sinking of shafts or the 

driving of entries through rock:

For use where the texture of the material is very tough and hard, 

as in tough granite, hard bowlders, and the like, 60

Various explosives i i i , .

for use in sinking per cent straight nitroglycerm dynamite is recomshafts and driving mencied. Where the material is of moderate tough6ntri6S

ness and somewhat brittle, 50 per cent straight nitroglycerin dynamite is recommended. In material such as limestone

and sandstone, 40. per cent straight nitroglycerm dynamite is recommended. In hard earth or compact sand, a 30 to 20 per cent straight 

nitroglycerm dynamite is recommended. , In material such as a soft 

crumbly or seamy rock that requires a stronger explosive than black 

blasting powder, but a slower explosive than dynamite, a granulated 

powder. containing 5 per cent of nitroglycerin is recommended. 

This should always be fired with a priming stick of dynamite. With 

this exception, different kinds of explosives should never be used in 

the same bore hole.

;vFor very,, soft work in cuts and fills, or for quarry work when 

dimension atone is sought, black blasting powder is recommended. 

In grading work the blast hole may be bottomed out with dynamite 

before charging with granulated powder or with black- blasting 

powder, but before it is charge<J/e> ar,e,.should be taken to see that the 

dynamite charge has not lef,t any. fire in the hole. In plastering or 

adobe work? on bowlders and spawls^.pr in block holing, a strong 

dynamite should be used. Block holing is the.more effective and 

economical method'for use with bowlders!' '

If the straight nitroglycerin dynamites, as recommended above, 

are found to be too quick or too violent for use, and 

the results obtained are not as desired under the given 

circumstances, ammonia dj^namites, which give a 

more heaving and rending action, are recommended. They are 

made in several grades and are rated as of a certain percentage of 

strength, but this rating is not always made in a scientific way. The 

following composition is an example of that which is generally offered 

in this country as a 40 per cent strength ammonia dynamite:

Composition of 40 per cent strength ammonia dynamite.

Per cent. 

Nitroglycerin.................................................... 22

Ammonium nitrate ............................................... 20

Dope........................................................... 58

Ammonia dynamites.
54 A PEIMEE ON EXPLOSIVES FOE COAL MINEBS.

This composition does not contain so large a percentage of nitroglycerin as the straight 40 per cent dynamite (see p. 19), and as 

tested at the Pittsburg testing station it is not found to produce the 

same results as the latter. Nevertheless the ammonia dynamites 

are often found to be more economical and more efficient for certain 

classes of work than the straight dynamites of the same commercial 

rating. The ammonia dynamites are less readily set off and are 

safer to handle, transport, and store than the straight 

dynamites are, but they all require stronger detonators than the straight dynamites to insure a complete and rapid detonation. They have the disadvantage, compared 

with the straight dynamites, of taking up moisture very readily, 

and great care should be used in storing them or in using them in 

wet holes.

For use in very wet blasting and in places where there is poor 

ventilation the gelatin dynamites are recommended.

Gelatin dynamites. - ,.,, , , ...,-, . , ,-. , , , Water has but little enect on them, and on complete 

explosion they yield only a small quantity of fumes and bad gases. 

Like ammonia dynamites, gelatin dynamites are less sensitive than 

straight nitroglycerin dynamites, and they therefore require stronger 

detonators to cause their complete explosion. They become less sensitive during long storage-, and they have been known after long storage in tropical countries to become so insensitive that they could 

not be detonated by means of the devices ordinarily used in firing 

them. Gelatin dynamite is likely to decompose during storage in 

very hot places.

Like the ammonia dynamites, the gelatin dynamites are sold in 

several grades and are given a somewhat unscientific rating in commerce. The grade known as 40 per cent strength gelatin-dynamite, 

as generally offered in this country, has the following composition:

Composition of 40 per cent strength gelatin dynamite.

Per cent.

Nitroglycerin.................................................... 32

Soluble nitrocellulose............................................. 1 . Dope............................................................ 67

As tested at the Pittsburg testing station, gelatin dynamites have 

not been found to be equivalent in every respect to straight nitroglycerin dynamites of the same commercial rating, and as regards 

economy they should seldom be used as equivalent; but they are 

superior for some uses, as mentioned above.
merce

SAFE SHIPMENT AND STORAGE OF EXPLOSIVES. 55

SAFE SHIPMENT AND STORAGE OF EXPLOSIVES.

By B. W. DUNN.

A responsibility to the public rests upon both manufacturers and 

common carriers to secure the safe delivery at clestit0 nation of explosives, and it is the duty of the owners 

of explosives to store them safely.

Under authority granted by Congress, the Interstate Commerce

Commission has made regulations, binding upon ship- Federal law and * ,1 , ^ e

interstate Com- pers and common carriers, tor the transportation ot

commission explosives in interstate commerce, and the penalty. 

of a possible fine of $2,000 and eighteen months' imprisonment is prescribed by law for a violation of any of these 

regulations. 

The shipper must know and certify on his shipping order that the1

explosive offered by him is in a proper condition for safe transportation and that it is packed and marked as required by the regulations. 

To perform this duty the shipper should be thoroughly familiar with 

all requirements pertaining to his shipment. A copy of the regulations can be obtained by application to the railway agent, whose 

duty it is to furnish them to shippers.

The following paragraphs in these regulations are of special interest to the shippers of explosives used in mines: General Rule A. 

Paragraphs 1501, 1502, 1503, 1509, 1510, 1531, 1533, 1541 to 1556, 1558 

to 1560, 1611 to 1614, 1648, 1661, 1665, 1666, 1668, 1674 to 1683.

Miners and other persons are sometimes tempted to pack explosives 

for shipment with their baggage on passenger cars, or

Explosives m bag- w^n ^nejr household goods for shipment by freight.

gage or household mi,,.. i ^ ^ A j ±u r

goods. I o do this is a criminal act that may endanger the lives

of the innocent and unsuspecting persons who have

to handle these packages, and that will subject the guilty shipper,

when detected, to arrest and prosecution. The federal law (section

236) prescribes an imprisonment of ten years for anyone convicted

of this crime when death or bodily injury results from the illegal

transportation of explosives. When no injury results, the maximum penalty is eighteen months imprisonment and a fine of $2,000.

There is no standard type of storage magazine in use in this country,

and the laws and regulations in foreign countries

ingsaeaZlne bUUd" applicable to the construction of magazines differ

materially. In Austria, for example, they are required to be of light construction, while in England they must have

walls at least 18 inches thick.
56 A PEIMEE 0$ EXPLOSIVES FOE COAL MINEES.

.8"* 8"brick pier

6"x 8" sill

- 6'0' 

8"brick wall

6'0"- 

...A

KGround

I8'0 

A

-2'tO"-

J_

9'o

Ventilator holes spaced 5'centers

line

B

FIGURE 11. Foundation plan (A), front elevation (B), and plan of ventilator hole (C) of brick magazine.
SAFE SHIPMENT AND STORAGE OF EXPLOSIVES. 57

No. 24 gage corrugated 

galvanized iron roof ,

2 "X4"purlins spaced 

to secure iron roof to.

galvamiei 

' iron 

\corn/ce

L ». l"x 6''lining

-j * Z "x 2 "strips spaced 3 'centei

2"x IZ" Joists st

Ground

* ! Zl"-*

Jl

"y.f? matched flooring

laced14 apart

"center sill 

line

_ __> __ __ , ,,__ __ -

140 

t 3I»\ J

<2"*.4" pur/ins {

|

/

brick 

wall

S

1 y

This space filled with 

N0.24^e corrugated . / asbestos fiber 

galvanized iron roof ,n ,n ... *% 'matched boards / *c Xj rafters f /

^H 

\

\\ 

i

\

RK IM /

s

\\

\\

--J'- H 3'-

t

/"xs

l"x /,?

X

'lining

\\

\\

-11 - s

I H /B E

 +2"x2 "fining 'stry> 

^ a'Vs"

.. ...j,,^ inter

\ \ asbes

I

^t

~TT

|| /

II

"\\base board \ \ -t

^~^ ./4"-

 2/WKj bridging

 s'o" -

m ^ s Vi.

] U [J EJ L

t"x 6"cei/ing Joists \ 

spaced 18' centers

rafters spaced J 'centers \ 

'tning spaces filled with 1 

tos fiber

>"* 12 "Joists \

i J S : \ S , ^

6 "x 8 "cen ter sill

 8"-

pter Ground line\

*k e'o"- 

B

per

-»f«-

\ \ i I

1'

"«0

\

brick 

to//

r?Ho. 26 

gage 

galvanized 

iron 

cornice

- 6'0" H 

1

FIGURE 12. Sections of magazine: A, section at line CD in fig. 11, B; B, section at line AB in fig. 12, A.
58 A PRIMER OF EXPLOSIVES FOR COAL MINERS.

Explosives should be protected as far as practicable during storage 

against heat, moisture, fire, lightning, projectiles, and theft. The 

buildings should therefore be weatherproof, covered by fireproof 

and bullet-proof material, well ventilated, in secluded locations, and 

not beside grass or underbrush subject to fire risk. Lightning protection is best placed on a line of supports encircling the building 

and ^0 to 30 feet distant from it. Figures 11 and 12 show plans of 

an approved type of magazine.

It is difficult to state definitely safe distances to separate magazines from dwellings, highways, railroads, etc. The 

Pr°Per distance must vary, evidently, with the 

amount of explosives stored and the degree of natural 

protection afforded by the slope of the ground and of artificial protection, such as barricades or mounds of earth.

The distances prescribed by the English law have been adopted by 

the State of Massachusetts. They are materially greater for large 

quantities of explosives than those prescribed in other countries. 

For example, the distances from a railway or public highway prescribed for a magazine containing explosives without natural or artificial protection are: For 1,000 pounds England, 630 feet; Prussia, 

984; Austria, 984; Italy, 244; for 10,000 pounds England, 795 feet; 

Prussia, 1,968; Austria, 1,640; Italy, 328; for 80,000 pounds England, 2,160 feet; Prussia, 1,968; Austria, 984; Italy, 574.

These distances may be materially reduced, in some places to onehalf or even to one-quarter, where there is good natural or artificial 

protection.

Magazines should be kept clean and in thorough repair. Grounds 

around them should be kept clear of leaves, grass, 

or other materials that might feed a fire. These 

Words should be conspicuously posted on them: "Explosives dangerous. No shooting allowed." The floors must be swept regularly and kept clean. The sweepings should be thrown in water or 

taken to a safe distance and destroyed.

In case floors become stained with nitroglycerin, cover the stains 

with dry sawdust, sweep up, and remove the sawdust. Then scrub 

the stains thoroughly with a hard brush and a solution of one-half 

pound of sulphide of sodium or sulphide of potassium in one-half 

gallon of wood alcohol.

Do not allow in the magazine any tools -other than a wooden mallet 

and wooden wedge, or a phosphor-bronze chisel, and a screw-driver 

to be used only for removing screws.

Do not open dynamite boxes with a nail puller or powder cans with 

pickaxes.

Remove all explosives before repairing a magazine.

Do not store detonators with explosives, especially high explosives.

Do not open packages of explosives in a magazine.
SAFE SHIPMENT AND STORAGE OF EXPLOSIVES. 59

Issue first the oldest explosives on hand.

Do not store dynamite boxes on end, as this increases the danger 

of nitroglycerin leaking from the cartridges.

Persons receiving packages of explosives sent by rail should examine them carefull}7 to discover ruptures or other serious damage 

during transit. Any information regarding such matters will be 

welcomed by the Chief Inspector, Bureau for the Safe Transportation of Explosives, 24 Park place, New York City.
APPENDIX. i

U. S. GEOLOGICAL SURVEY TEST REQUIREMENTS FOR EXPLOSIVES.

The tests will be made by the engineers of the United States explosives testing 

station at Pittsburg, Pa., in gas and dust gallery No. 1. The charge of explosive to 

be fired in tests 1, 2, and 3 shall be equal in disruptive power to one-half pound (227 

grams) of 40 per cent nitroglycerin dynamite in its original wrapper, of the following 

formula:

Nitroglycerin................................................... 40 _

Nitrate of sodium................................................ 44 "

Wood pulp....................................................... 15

Calcium carbonate............................................... 1 "-E

100 ~^

Each charge shall be fired with an electric detonator of sufficient power to completely^ 

detonate or explode the charge, as recommended by the manufacturer. The explosive 

must be in such condition that the chemical and physical tests do not show any 

unfavorable results. The explosives in which the charge used is less than 100 grams 

(0.22 pound) will be weighed in tinfoil without the original wrapper.

The dust used in tests 2, 3, and 4 will be of. the same degree of fineness and taken 

from one mine, to insure uniformity of composition and inflammability.

Testl. Ten shots with the charge as described above, in its original wrapper, 

shall be fired, each with 1 pound o- of clay tamping, at a gallery temperature of 77° 

F., into a mixture of gas and air containing 8 per cent of methane and ethane. An 

explosive will pass this test if all 10 shots fail to ignite the mixture.

Test 2. Ten shots with charge as described above, in its original wrapper, shall 

be fired, each with 1 pound a of clay tamping, at a gallery temperature of 77° F., into a 

mixture of gas and air containing 4 per cent of methane and ethane and 20 pounds 

of bituminous coal dust, 18 pounds of which is to be placed on shelves laterally 

arranged along the first 20 feet of the gallery, and 2 pounds to be placed near the 

inlet of the mixing system in such a manner that all or part of it will be suspended 

in the first division of the gallery. An explosive will pass this test if all 10 shots 

fail to ignite the mixture.

Test 3. Ten shots with charge as described above,- in its original wrapper, shall 

be fired, each with 1 pound a of clay tamping, at a gallery temperature of 77° F., 

into 40 pounds of bituminous coal dust, 20 pounds of which is to be distributed uniformly on a horse placed in front of the cannon and 20 pounds placed on side shelves 

in sections 4, 5, and 6. An explosive will pass this test if all 10 shots fail to ignite 

the mixture.

Test 4- A limit charge will be determined within 50 grams by firing charges in 

their original wrappers, untamped, at a gallery temperature of 77° F., into a mixture 

of gas and air containing 4 per cent of methane and ethane and 20 pounds of bituminous coal dust, to be arranged in the same manner as in test 2. This limit charge is 

to be repeated five times under the same conditions before being established.

Subject to the conditions named below, a permissible explosive is defined as an 

explosive which is in such condition that the chemical and physical tests do not

o Two pounds of clay tamping are used with slow-burning explosives. 

60
APPENDIX. 61

show any unfavorable results, which has passed gas and dust gallery tests Nos. 1, 2, 

and 3 as described above, and of which in test No. 4 the limit charge has been 

established at or above 1$ pounds (680 grams).

Provided: 1. That the explosive is in all respects similar to the sample submitted 

by the manufacturer for test.

2. That No. 6 detonators, preferably No. 6 electric detonators (double strength),

are used of not less strength than 1 gram charge, consisting by weight of 90 parts of

mercury fulminate and 10 parts of potassium, chlorate (or its equivalent), except for

. the explosive "Masurite M. L. F.," for which the detonator shall be of not less strength

than 1£ grams charge. '

3. That the explosive, if frozen, shall be thoroughly thawed in a safe and suitable 

manner before use.

4. That the amount used in practice does not exceed 1$ pounds.

SURVEY PUBLICATIONS ON MINE ACCIDENTS AND EXPLOSIONS.

The following publications, except Bulletin 369, can be had free by applying to the 

Director, U. S. Geological Survey, Washington, D. C. Bulletin 369 can be had by 

sending the price, in cash, to the Superintendent of Documents, Government Printing Office, Washington, I). C.

BULLETIN 333. Coal mine accidents: their causes and prevention a preliminary 

statistical report, by Clarence Hall and W. 0. Snelling, with introduction by J. A. 

' Holmes. 1907. 21pp.

t BULLETIN 369. The prevention of mine explosions. Report and recommendations,

, by Victor Watteyne, Carl Meissner, and Arthur Desborough. 1908. llpp. 5 cents.

BULLETIN 383. Notes on explosive mine gases and dusts, with special reference to

the explosions in the Monongah, Darr, and Naomi coal mines, by E. T. Chamberlin. 1909. 67pp.

o