IMPROVEMENTS IN THE PREPARATION OF NITRO- GLYCERIN COMPOUNDS
Year: 1881

page_text: LETTERS PATENT to Gilbert Smith Dean, of the City and County of San
Francisco, State of California, one of the United States of America, Chemist,
"
for an Invention of IMPROVEMENTS IN THE PREPARATION OF NITRO-
GLYCERIN COMPOUNDS."
COMPLETE SPECIFICATION filed by the said Gilbert Smith Dean at the
Office of the Commissioners of Patents on the 21st May 1881.
GILBERT SMITH DEAN, of the City and County of San Francisco, State of
California, one of the United States of America, Chemist. IMPROVEMENTS IN
THE PREPARATION OF NITRO-GLYCERIN COMPOUNDS."
The object of this Invention is the preparation of a new variety of nitro-glycerin
compounds. The results sought are mainly as follows:-
First. The production of a compound which shall have greater breaking power
than pure nitro-glycerin, which shall be solid and free from leakage, which shall be
sufficiently plastic to enable the bore-hole to be completely filled, and the full force
of the explosive to be thereby obtained.
Second. The preparation of said compound in such a manner as to permit of its
ready and complete admixture with common blasting powders.
Third. The increasing of the safety of the aforesaid compounds and of nitro-
glycerin compounds in general.
The manner of accomplishing the result desired is as follows:-
I first prepare a new variety of nitro-dextrin by the process hereinafter described.
I then mix the nitro-dextriu as hereinafter specified. Common blasting powders or
other materials may be added to the compound during the process of manufacture.
I then allow the mixed material to stand and "set." When first mixed it forms
a liquid or paste, but it speedily hardens to a proper consistency. Increased
safety is secured by mixing inexplosive liquids with the compound during the
process of manufacture, as hereinafter described.

page_text: "
The first step of the process is the preparation of the nitro-dextrin. The
material used for this purpose is old cotton rag which has been thoroughly
bleached. Unbleached cotton, hemp, &c., may be used, as may be "wood pulp
(that is, wood which has been thoroughly ground and bleached), but wood in the
form of saw dust or shavings is useless. The first named material (i.e., old cotton
rag) is that which I consider best.
The preparation of the nitro dextrin (the crude material having been selected as
above) divides itself naturally into three stages.
1. The preparation of the material.
2. The nitration.
3. The washing.
The object of the first stage is to start the conversion of the cellulose into dextrin.
To this end the rag is immersed in hot dilute mineral acid, i.e., sulphuric, nitric, or
hydro-chloric, or a mixture of two or more of these acids. The kind of acid used
is not important, nor is it necessary (or even desirable) that the dextrination be
completed during this preliminary process, for if it be once fairly started it will be
continued and completed in the nitration process to be presently described.
The most convenient acid to use for this purpose is nitric, for where this (or
hydro-chloric) is used it is simply necessary to immerse the rag in the acid, heat it
till it becomes tender, and then dry the rag without washing. This is because of
the volatile nature of these acids. But the cheapest acid for this purpose is the
waste mixture of sulphuric and nitric, the residue (or waste acid) of the nitration
process.
I shall therefore describe the process as followed with this waste acid, premising
however that if commercial acid of any kind be substituted it should be diluted
with four or five times its volume of water, and that if a volatile acid is used the
washing process may be omitted.
It will be seen that this preliminary process (termed "cutting" by the workman)
is somewhat similar to the preparation of "parchment" from paper, or the pre-
paration of dextrin and glucose from starch. 1 place the acid in a pot or boiler
of porcelain or other acid proof material and heat it nearly or quite to boiling.
The rag being immersed in the hot acid is watched by the operator; as fast as it
becomes tender he removes it, and replaces it by fresh rag.
It is not generally desirable that the boiling be continued until the fibre is
completely broken down, for in that case it becomes more difficult to wash; but
there is a point easily known after one or two trials where the action of the acid is
sufficient, yet where the fibre is not as completely destroyed as to render the
washing slow and tedious. This point is judged by the tenderness of the rag; it
should be as tender as possible, yet not reduced to a pulp. If "overcut," and
thereby reduced to pulp or powder it may still be used, but as before stated it
becomes difficult to wash.
After the removal from the boiler the material is thoroughly washed either with
water or weak alkaline solutions, or both, till all acid is removed, the washing
being in all cases completed with water. It is then thoroughly dried and cooled,
and is ready for the next operation.
This operation somewhat resembles the preparation of nitro-glycerin, being
conducted with cold acids, stirring and cooling.
For the nitration I use a mixture of about six parts by weight of the strongest
sulphuric acid, and two parts by weight of the strongest nitric, adding thereto one
part by weight of the prepared material. It is desirable that these proportions be
not widely departed from, for experience has shown that one part of the dry
material requires not less than one and three fourths (1 3/) parts of strong nitric

page_text: acid (48° to 50° Baume) for its nitration, and requires at least seven parts of mixed
acid to form a mass sufficiently liquid for pouring. The acids are of course mixed
and allowed to cool before using.
The mixed acids may be placed in a tank and the dried material added and
stirred in, but I prefer to draw into the tank alternately or simultaneously and
gradually the mixed acid and the organic material with a view to obtaining a
product as nearly uniform as possible. Constant stirring is kept up during the
operation, and care is taken that all the material used be in a cool state, and that
heating of the tank and its contents be prevented by external cooling. In these
respects the process resembles that ordinarily followed in the manufacture of
nitro-glycerin.
"
When all the materials have been introduced into the tank and the whole
thoroughly stirred together until the process is finished, the nitro-dextrin should
now be in a state of quasi solution in the acid, resembling "mush
or thick ropy
mucilage. If however it be so thick that it will not pour out readily it must be
thinned by the addition of more strong acid.
"
The perfection of the result depends largely on the perfect management of the
preliminary process described, termed by the workmen the cutting," for if the rag
be not sufficiently "cut" it nitrates in the strong acid but does not dextrinate, and
consequently retains its original form of rag. It appears in fact that the process
of dextrination must be fairly started in the preliminary operation, and that when
so started it is continued in the strong acids pari passu with the nitration. If
therefore the rag be withdrawn from the "cutting" acids before it has become very
tender it may yield some nitro-dextrin, but will give principally nitro-cellulose;
whereas, if the "cutting" process be pushed sufficiently far complete dextrination
will take place in the nitrating acids.
The nitration process being finished, the mixture of acids and nitro-dextrin
should be drawn off into water.
Special precautions are here necessary to prevent decomposition of the nitro-
compound, for though it appears in a state of semi-solution in the acid it precipitates
immediately when drawn into water.
It is therefore necessary, first, that a somewhat larger volume of water be used
to receive the mixture, say about eight or ten times the amount of the acid mixture,
still more water is better. If the water becomes more than lukewarm during the
washing its quantity is insufficient. Second, that the water be violently agitated
and beaten up while the mixture is flowing into it. Third, that the mixture be
not added to the water in a lump, but be poured in gradually and not too rapidly.
Without these precautions there is certain to be more or less of overheating and
decomposition. The nitro-dextrin falls to the bottom of the washing tank, whence
it is withdrawn and washed and freed from acids by simple and well known
processes.
I regard a granular semi-crystalline appearance of the finished product as evidence
that the "cutting" has been well conducted, and I regard the combustion of the
finished article without leaving any evidence of carbonaceous residue, as evidence
that a sufficient amount of strong nitric acid has been employed, and that the
washing has well conducted; the nitro-dextrin however is scarcely so combustible
as the fibrous nitro-compounds.

page_text: desired compound. To this end one part of nitro-dextrin (prepared as described)
is thoroughly mixed with from one to three parts of nitro-glycerin, and the
mixture is allowed to stand from one to two hours that perfect combination may
take place.
When first mixed the compound is a liquid or paste, but it speedily hardens or
"sets" (like plaster) to a proper consistency for use in blasting. The best consistency
for most uses is obtained by the employment of one part of nitro-dextrin to three
of nitro-glycerin. A larger proportion of nitro-dextrin produces a compound of
greater distinctive force but of less specific gravity.
This combination may be mixed with ordinary blasting powder, or such
modifications thereof, as may suit particular uses.
It is in fact admirably adapted to form a compound of such mixtures, as the
nitro-glycerine being held by the nitro-dextrin, may be combined with the powder
in any desired proportion, and all danger of leakage of nitro-glycerin from the
material is avoided by the strong affinity existing between the nitro-glycerin and
the nitro-dextrin.
In preparing mixtures of this kind I mix the nitre, sulphur, and charcoal (or
other organic material which may replace the charcoal) with the nitro-dextrine.
The nitro-glycerin is added, and the mixture left till the "setting" or hardening
of the compound has taken place, when it is again mixed and packed in cases
for use.
We have thus by means of the nitro-dextrin a method of combining nitro-
glycerin in any proportion with any powder whatever, and are consequently able
to produce powders adapted to any and every kind of work.
In order to increase the safety of the (nitro-glycero nitro-dextrin) compound
herein described, as indeed to increase the safety of nitro glycerin compounds in
general, I mix with the compound an inexplosive liquid in such quantity as to
give the degree of safety desired.
Water is the liquid which I prefer for this purpose, provided steps are taken to
prevent its evaporation, such as packing the explosive in boxes containing damp
sawdust, or using a deliquescent salt to impede the evaporation of the water.
Non volatile liquids may be used instead of water, but are more expensive and
generally produce a material which is more inflammable. It is however extremely
safe agaiust explosion.
The best method of combining these inexplosive liquids with compounds of
nitro-glycerin is to add them to the solid portion of the nitro-glycerin compound,
and after they have become evenly distributed through the mass to add the
nitro glycerin and mix thoroughly. By this means a perfect combination may be
obtained between the nitro-glycerin and any liquid whatever.
Five per cent. of an inexplosive liquid added to a nitro-glycerin compound
increases its safety to a remarkable degree. When the proportion of the inexplosive
liquid is raised from ten to twenty per cent. of the compound it becomes inexplosive
by the ordinary detonators, and is apparently useless. But it may (when the limit
of explosibility in the open air has been passed) be readily exploded when firmly
confined in rock or iron.
It might be supposed that the admixture of water would destroy the usefulness
of combinations of nitro-glycerin and blasting powder, but such is by no means
the case.
Having thus described my Invention, what I claim as new and desire to securo
by Letters Patent is,―
1st. The nitro-dextrin prepared as described.
2nd. The compound of nitro-dextrin and nitro-glycerin prepared as described.
וה

page_text: 4th. The method of increasing the safety of nitro-glycerin, consisting in
combining therewith an inexplosive liquid in the manner described.
In witness whereof, I, the said Gilbert Smith Dean, have hereunto set my
hand and seal, this Twenty second day of April, A.D. One thousand eight
hundred and eighty one.
Witnesses,
S. H. NOURSE,
JEROME T. KENDALL.
GILBERT SMITH DEAN. (L.S.)