GEOLOGICAL SURVEY CIRCULAR 161 

COMPILATION OF FIELD METHODS 

USED IN 

GEOCHEMICAL PROSPECTING 

BY THE 

U. S. GEOLOGICAL SURVEY 

By H. W. Lakin, Hy Almond, and F. N. Ward 
UNITED STATES DEPARTMENT OF THE INTERIOR 

Oscar .L. Chapman, Secretary 

GEOLOGICAL SURVEY 

W. E. Wrather, Director 

GEOLOGICAL SURVEY CIRCULAR 161 

COMPILATION OF FIELD METHODS- USED IN GEOCHEMICAL PROSPECTING 

BY THE U. S. GEOLOGICAL SURVEY 

B, H. W. Lakin, Hy Almond, and F. N. Ward 

Washington, D. C,.1962 . 

'Free-on appHation to the Geol~cal Surve,Y, WuhinctOii 25, D. C. 
CONTENTS 

Page Page 

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . 1 Methods of analysis. --Continued 

Special reagents and apparatus . . . . . . . • . . 1 Preparation of soils and rocks for 

Special reageants . . . . . . . . . . . . . . . . . 1 

Dithizone . . . . . . . . . . . . . . . . . . . 1 

Dimethylglyoxime. . . . . . . . . . . . 2 

Rubeanic acid . . . . . . . . . . . . . . . 2 

2-nitroso-1-naphthol... . ..... 3 

p-Dimethylaminobenzalr hodanine . • . • . . . . . . . . . . . . . . 3 

Potassium thiocyanate........ 3 

Special apparatus . . . . . . . . . . . . . . . . . 3 

Chromograph. . . . . . . . . . . . . . . . 3 

Stevens Extraction Stick . . . . . . 5 

Huff antibump test tube . . . . . . . 5 

Apparatus for preparation of 

metal-free water........ . . ..• 5 

Digestion and fusion rack . . . . . 5 

Fusion rack................. 5 

Sieves.. . . . . . . . . . . . . . . . . . . . . 5 

Toxicity of reagents. . . . . . . . . . . . . . . . . . . . 7 

Carbon tetrachloride.............. 7 

Amyl alcohol. . . . . . . . . . . . . . . . . . . . • 7 

Isopropyl ether................... 7 

Potassium cyanide. . . . . . . . . . . . . . . . 7 

Hydrofluoric acid. . . . . . . . . . . . . . . . . 7 

analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . • • 12 

Determination of heavy metals in 

soil or sediment. . . . . . . . . . . . . . . . . . . . . 12 

Determination of zinc in soils .......... · 14 

Chromographic determination of 

nickel in soils and rocks. . . . • . . . . . . . . . 16 

Chromographic determination of copper 

in soils and rocks . . . . • . . . . . . . . . . . . . . • 18 

Determination of cobalt in soils and 

rocks............ . . . . . . . . . . . . . . . .. . . 19 

Determination of molybdenum in soils 

and rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Determination of lead in soils 

and rocks . . . . . . . . . . . . . . • • . . . • . • . . . . . 21 

Determination of silver in soils and 

rocks ............................... 22 

Determination of tungsten in soils .....•. • 24 

Determination of readily soluble copper, 

zinc, and lead in soils and rocks: · 

sulfuric acid extraction ............... 25 

Determination of zinc in plants. . . . . . . . . . 27 

Determination of nickel in plants. . . . . . . . 28 

Determination of molybdenum in 

Purification of reagents . . . .. . . . . . . . . . . . • . . 7 

Methods of analysis . . . . . . . . . . . . . . . . . . . . . . . . . 9 

Explanatory notes . . . . . . . . . . . . . . . . . . . . . 9 

Determination of heavy metals 

plants ...........•••..............•.. 29 

Appendix. . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . 31 

Reagents required for 1, 000 

determinations by each method ......... 31 

in water.......... . . . . . . . . . . . . . . . . . . . 9 References cited. . . . . . . . . . . . . • . . . • . . . . . . . . . . 34 

ILLUSTRATIONS 

Page 

Figure 1. Original plastic model of chromograph. . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Table 

2. Kit containing two all-glass chromographs. • . . . • . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . 6 

3. Stevens Extraction Stick • . . . . . . . . . . . . • . . . • . . . . . . . . . . . . .. • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . 6 

4. Huff antibump test tube . . . . . . . . . . . . . . . . . . . . . . . . . • . . . • . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . • . 8 

5. Digestion and fusion rack . . . . . . . . . . . . • . . . . . . • . • . . . . • . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

6. Fusion rack ...•....... · .................•.•....• ·. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

7. Aluminum sieve and holder ..............•..•...• ; ....•..................................•.. 10 

1. 

2. 

3. 

4. 

5. 

Page 

TABLES. 

Comparison between average metal content of igneous rocks and minimum content detected by 

field methods described in this compilation................................................. 2 

Descriptio·n of colors with heavy metals test on standard solutions (according to Huff) ....••••.••• 11 

.Supplemental determinations for heavy metals 4t.:wa,ter: (according to Huff) . . . . . . . . . . . . . . . . . • . . . . • 12 

Descriptive chart of .color of dithizone solution for.determination ·of heavy metals 

(expressed as zinc equivalents) ....••...•.•..••.••••••••••.... _. • • . . . . . • .. . . . . . . . . . . • • • • • . . • • 15 

Zinc content of plants corresponding to various voiumes of sample · so1ution • . • • . • • . • . • • . . . • . • . . . • 28 
COMPILATION OF FIELD METHODS USED IN GEOCHEMICAL PROSPECTING 

BY THE U. S. GEOLOGICAL SURVEY 

INTRODUCTION 

The field methods described in this repo,rt are 

those currently used in geochemical prospecting by the 

U. S. Geological Survey. Some have been published, 

others are being processed for publication, while 

others are still being investigated. The purpose in 

compiling these methods is to make them readily 

available in convenient form. The methods have not 

been thoroughly tested and none is wholly satisfactory. 

Research is being continued. 

These methods, developed to meet the needs of 

geochemical prospecting, (Hawkes, 1950), possess 

speed, simplicity , and a moderate amount of accuracy. 

Each method permits as many as 25 to 30 determinations in an ordinary day. Separations and other 

chemical operations are held to a minimum, and in 

as far as possible, the required apparatus is restricted to common laboratory equipment. Moreover, the 

methods are designed to give positive tests for background material (see table 1) and results within 30 

to 50 percent of the correct value for materials 

containing abnormal amounts of the element. 

. Two types of colorimetric procedures are used 

in the methods o'f estimation. The first type used in 

the methods for the determination of zinc, lead, 

molybdenum, tungsten and heavy metals, is extraction of an aqueous solution whereby a colored solution 

of the desired constituent is obtained in an immiscible 

solvent. The intensity or shade of the color is proportional to the quantity of the metal present. The second 

type of colorimetric p;rocedure, used in the methods 

for the determination of copper, nickel, cobalt, and 

silver, is a confined spot test procedure. A colored 

precipitate is obtained in a fixed area, the intensity 

of the · color being a function of the quantity of the metal 

present. 

Both methods of estimation have advantages and 

disadvantages. The extraction procedures require a 

minimum amount of simple ~d easily· assembled 

equipment; the confined spot test procedures require 

one moderately expensive piece of equipment. The 

extraction procedures reqUire a great deal of shaking 

of solvent with aqueous solution to effect extraction, 

and are ther_efore subject to a large personal factor; 

they also require the preparation of comparison 

standards with each group of samples analyzed. The 

spot test procedures are simpler to perform and the 

standards as well as the spots obtained by the test 

are semipermanent. 

The useful range ofboth extraction and confined 

spot methods depends on the minimum conc!=ntration 

of the element in solution giving a positiVE;! test 

(hereafter designated sensitivity, and on the concentration 

1 

of the element which produces a maximum color. 

As concentrations can be conveniently expressed in 

micrograms per milliliter, each method is characterized by a minimum number of micrograms per 

milliliter required to give a test, and by a maximum 

number of micrograms per milliliter, beyond which 

color differences are not perceptible. Because the 

quantity of a constituent present in a test solution 

is proportional to the size of the sample, by trial 

and error the weight of the sample can be increased 

until the concentration in the test solution of the 

constituent being determined is sufficient to give a 

positive test. However, the extent to which the 

sample size (!an be increased, while the volume of 

the sample solution is held constant, is limited. 

When the ratio of the weight of the solution in which 

the sample is dissolved to the weight of the sample 

exceeds about 50, several things may happen. For 

example, if 0. 1 g of sample is dissolved in 2. 5 ml 

of solution--ratio of weight of solution to weight of 

sample is 25--salts of the major constituents may 

precipitate as the solution cools. Silica may separate, 

and frequently salts resulting from the neutralization on the acid or alkaline attack of the sample may 

crystallize. Such difficulties impose a practical 

limit to the ratio of the weight of sample solution to 

the weight of sample. This ratio and the sensitivity 

of the reaction determine the · smallest concentration 

of a given constituent which can be estimated by these 

field methods. The concentration of the element 

producing a maximum color governs the largest 

concentration of the given element which can be determined by these methods except as one takes smaller 

. aliquots. The reliability of results obtained on the 

latter types of materials is largely dependent on the 

accuracy with which smaller aliquots can be measured. 

Special Reagents 8.nd Apparatus 

Before the methods are presented, a brief 

discussion of some important reagents and special 

apparatus is d!?sirable. A more complete discussion 

of the reagents will be found in the excellent treatises 

of Feigl (1946, 1949), Flagg (1948), Sandell (1950), 

Welcher (1948), and Wenger and Duckett (1948). All 

of the special apparatus and reagents (analytical 

grade) are commercially available. 

Special Reagents 

Dithizone (diphenylthiocarbazone), first 

investigated as an analytical reagent by ·Hellmut 

Fischer (1925), is nowlquite widely used. Sandell 

(1950, p •. 87) and Welcher (1948, Vol. ill, p. 463) 

give in detai 1 very satisfactory accounts of its 

analytical properties and applications. The violet 
Table 1.--Comparison bet~een average metal content of igneous rocks and minimum content 

detected by field methods described in this compilation. 

Average content of Minimum content detected 

Metal igneous rocksl by field method 

(ppm) (ppm)2 

Zinc ------------------ 132 50 

Nickel ---------------- Bo 15 

Copper ---------------- 70 10 

Cobalt ---------------- 23 10 

Molybdenum ------------ 2.5 - 15. 1 

Lead ------------------ 16 10 

Silver ---------------- .1 .2 

Tungsten -------------- 1.5 - 69. 10 

lAverages given by Rankama and Sahama in Geochemistry, table 2, 3, pp. 39-40, Chicago, Ill. 

The University of Chicago Press, 1950. 

2ppm = parts per million; 1 ppm = 0.0001 percent. 

black solid is insoluble in acid solutions, soluble in 

alkaline solutions and in almost all organic solvents. 

Carbon tetrachloride, in which dilute solutions of 

dithizone are green, is the sol vent used in the methods 

described tn· this compilation. 

Dithizone forms internal complex salts with 

many metals. The so-called dithizonates, can be 

formed by shaking the carbon tetrachloride solution 

of dithizone with an aqueous solution of the metal. 

The dithizonates, usually soluble in the organic sol vent, 

impart to it a violet, red, orange, or yellow color, 

depending on the metal involved. 

Dithizone reacts with about seventeen metals to 

form colored dithizonates, but its principal use as an 

analytical reagent has been confined to cobalt, copper, 

cadmium, bismuth, lead, mercury, silver, thallium, 

and zinc. The value of the reagent lies in the great 

sensitivity that can be obtained by its use; the sensitivity of dithizone methods is of the same order as that 

of spectrographic methods. Specificity for certain 

elements can be obtained with dithizone by careful 

control of pH and by use of complex forming agents 

which sequester other reactir~g metals. 

Two properties of the reagent must be kept in 

mind when dithizone is used under field conditions. 

First, the reagent is easily oxidized, particularly 

when exposed to sunlight and/ or heat, and both the 

color and strength of the solution are modified as a 

result. It may also be oxidized by certain constituents . 

of the sample solution, as for example, ferric iron in 

the presence of cyanide and citrate. The oxidation 

product, diphenylthiocarbodiazone, is soluble in 

carbon tetrachloride to which it imparts a yellow 

color, and is insoluble in aqueous solutions. This 

yellow color may be confused with that of such 

dithizonates as those of silver, mercury (II), thallium 

(III), and bismuth; in the determination of copper, 

zinc, and lead, the presence of the yellow oxidation 

product in the dithizone solution produces an offshade color which is difficult to compare with standards. 

2 

Dithizone, stored in a concentrated form in a dark, 

cool place is fairly stable. Webb and Millman 

(1950, p. 7) describe special precautions that ·must 

be taken when working with dithizone in a tropical 

climate. 

The second property of the reagent that must be 

kept in mind is the high sensitivity of dithizone for 

a large number of elements. Therefore, extreme 

care must be exercised to prevent contamination. 

Because a large number of elements reaCt with 

dithizone, the final extraction must be made in the 

presence of proper complexing agents and at the 

proper pH to make the reagent specific for the metal 

being determined. In the lead determination on. 

page 24, for example, the final estimation is carried 

out at pH 8. 5 in the presence · of potassium cyanide to 

insure specificity. 

Dimethyl~lyoxime, the reagent used in the test 

for nickel m this paper, is a white crystalline solid, 

only slightly soluble in water (0. 4 g per liter) and 

soluble in alcohol and acetone. Diehl (1940) has 

published an extensive discussion on the uses of 

dimethylglyoxime in analytical chemistry. Dimeth- ~lglyoxime reacts with nickel in acid, neutral, and 

ammoniacal solution to give a bright red, extremely 

insoluble complex compound. The reagent reacts with 

palladium in acid solution to yield an acid insoluble 

yellow compound. Copper (ll), cobalt (II) (III), and 

iron (II) form water soluble colored compounds. 

Rubeanic acid (dithiooxamide) is an orange-red 

crystalline compound, slightly soluble in water, 

alcohol, and acetone. In ammoniacal solutions, the 

reagent forms insoluble complex salts with copper, 

cobalt, and nickel, the colors of which are respectively black, brown, and blue. Copper rubeanate is 

the only one of these three precipitated from acetic 

acid solutions--a fact used in the copper test. In 

strong mineral acid solutions, rubeanic ac~d yields 

red' crystalline precipitates with palladium and 

platinum, and a soluble blue compound with ruthemum. 
2-nitroso-1-naphthol is a greenish-yellow 

· crystalhne sohd soluble m hot water and alcehol, and 

slightly soluble in ether. 

Like most of the organic reagents used in 

analytical chemistry, 2-nitroso-1-naphthol reacts 

with a number of metals to give relatively insoluble 

precipitates. It reacts with iron, copper, and 

zirconium, as well as with cobalt. However, like 

dithizone, the reagent can be made specific by proper 

adjustment of pH and the use of complexing agents. 

Thus in the cobalt test given later, the reagent is 

made specific for the element by precipitating from 

an acid solution (pH 6) in the presence of citric acid. 

p-Dimethylaminobenzalrhodanine is a red 

crystallme sohd, only slightly soluble in chloroform, 

benzene, and ether. It is insoluble in water, but 

dissolves in strong acids imparting a yellow color to 

the solution. 

Although in acid solution the reagent gives 

red or violet precipitates with silver, mercury, 

copper(!).', gold, and palladium, it is the most 

satisfactory reagent available for the determination 

of minute amounts of silver. 

Potassium thiocyanate has been used as a 

reagent for Iron, molybdenum, tungsten, rhenium, 

cobalt, niobium, and bismuth. The formation of a 

red compound between thiocyanate and iron (III) 

is the basis of a sensitive test for iron. In the 

presence of a reducing agent such as stannous 

chloride, molybdenum in weak acid solution forms 

an amber-colored complex ion and tungsten in strong 

acid solution forms a yellowish-green complex ion. 

Since the products in both cases are extractible with 

organic solvents, the reaction with thiocyanate 

followed by an extraction with isopropyl ether is the 

basis for the molybdenum and .tungsten methods. 

Special Apparatus 

The equipment required for the tests has been 

simplified as far as possible. To illustrate, test 

tubes are used for fusions in place of crucibles, for 

digestions in place of beakers, and with simple 

volume calibrations in place of volumetric flasks. 

Pipettes, wash bottles, reagent bottles, graduated 

cylinders, and test tube racks are also used. In 

addition to the above equipment and to certain special 

pieces of apparatus described later, the field methods 

included in this compilation require a source of heat 

and some means of measuring the sample. Depending 

on the accuracy desired, one can measure the sample 

size volumetrically by means of a calibrated spoon, 

or gravimetrically by means of a torsion balance. 

A balance with a sensitivity of 2 mg is adequate for 

the majority of the methods. A gasoline stove or an 

alcohol blowtorch can be used as a $ource of heat 

for fusions, and either of these or a small portable 

electric hot plate can be used for the digestions. 

Chromo~aph. The chromograph is a device 

for making coniriea spot tests on paper. A detailed 

description is given by Stevens and Lakin (1949). The 

device is used to confine areas of definite size on a 

strip of .paper fed through the apparatus and to 

control automatically the rate of flow of test solution 

3 

through the confined spot. The rate of flow of test 

solution through the paper is controlled by the uniform 

pull of a column of water {and/ or filtrate from previous 

tests) passing through a calibrated capillary. The 

paper in the form of strips is fed through the apparatus 

to .give a number of confined spots on each strip, the 

sample number being written on the strip near the 

corresponding spot. 

An early model of the chromograph is shown in 

figure 1. Two all-glass chromographs mounted in 

a portable case are shown in figure 2. The essential 

features of the chromograph are (1) filter head and 

filter base between which the test paper is secured, 

(2) a three-way stopcock connecting the filter base 

to the adjustor bu!b and, or, the settling bottle, 

(3) a settling bottle fitted with three pieces of capillary 

tubing to provide a choice of outlets. The critical 

dimensions are (1) the inside diameter of the passage 

through the filter head and filter base which fixes the 

diameter of the confined spot, (2) the length of the 

column of water supported above the capillary, and 

( 3) the internal diameter and length of the capillary. 

The height of the water column and the diameter and 

length of the capillary control the rate of flow of the 

test solution through the reagent paper. In the 

chromograph the diameter of the spot has been set at 

0. 25 in., and the height of the column of water at 

9 in. The lengths of precision-bore capillary tubing 

with an inside diameter of 0. 0065 in. have been set 

at 0. 75, 1. 5, and 2. 25 in. to provide rates of flow 

of 100, 200, and 300 sec. for passage of 0. 2 ml of 

solution without paper in the apparatus. 

The methods so far developed using the chromograph employ three types of precipitation reactions. 

1. With rea~ent papers. The paper is impregnated with a s Ightly soluble reagent which reacts 

with the sample solution, causing the ion sought to 

be precipitated. The solubility of the reagent must 

be such that it acts as an efficient precipitant without being completely removed during the passage of 

the solution. The determinations of copper and 

nickel in soils, to be desc_ribed, are ex8:mples. 

2. With reagents added to the s.olution. The 

reagent solutlbrr IS added to the test solution on an 

untreated paper in the chrO!IfOgraph head. The 

solutions are mixed by' bubbling air up through the 

paper by means of the adjustor bulb. The precipitate 

formed by the reaction is collected on the confined 

area of untreated paper, by reversing the stopcock 

and allowing the solution to flow through the capillary. 

The determination of cobalt in soils and rocks is an 

example of this type. 

3. With previously formed precipitate. The 

previously formed precipitate is dispersed and the 

dispersion is transferred to the chromograph head 

containing untreated paper. The precipitate is 

collected on the paper by opening the stopcock 

and. allowing the solution to pass through the capillary. 

The; determination of sn ver in soils is an example 

of this type. 

The colored spots obtained by these methods. 

are relatively stable and serve as a semipermanent 

record of the reS'.Qlts obtained. A standard series 
• 

Capillary protector 

plug 

Capi I lory __ _...,". 

Cleon;..out " plug · -~~-~ 

') ' 

---Filter head 

~_,;,_--Filter bose 

-~~-- 3 way stopcock ~~~~ 

1"11----· Adjustor bulb tube 

.,. __ Outlet tube 

Adjustor 

bulb 

Figure !.--Original plastic model of chromograph. 

4 
of spots is used to compare with the spots obtained 

on samples in much the same manner as a standard 

series of colored solutions are used to evaluate the 

sample solutions in visual colorimetry. However, the 

semipermanent nature of the confined spots makes 

y-equent preparation of standards unnecessary. · 

Stevens Extraction Stick. (Extractor for removing soluble conshtuent.s m chemical analysis. 

Patent applied for by Rollin E. Stevens.) Filtrations 

and extractions are made with a Stevens extractor. 

This device is made as follows: A medium porosity, 

fritted disc is fused in one end of a pyrex glass tube 

170 mm long and 7 mm inside diameter; a number 13 

ground glass joint provided with a number 13 stopper 

is fused on the other end. The tube is calibrated at 

2, .5, and 10 ml. A modified extractor can be easily 

made by constricting the glass tube near one end and 

packing the resulting small bulb with fine borosilicate 

glass fiber to serve as a filtering medium. In the 

molybdenum and tungsten procedures the ·simple 

extractor requires only cork stoppers; other procedures using strong, oxidizing acids require the 

ground-glass stopper. 

To make extractions with the extractor, the 

solvent and the extractor are placed in a test tube 

containing the sample or a fusion of the sample, with 

the filter end of the extractor pointing downward. 

See figure 3. The liquid in the test tube is then 

brought'.to a boil. Bumping is eliminated, at first by 

the release of air bubbles from the expansion of the 

air within the extractor, and later by the filter, which 

causes a continuous and gentle release of the superibeated . liquid from the many surfaces. While the 

solvent is boiling the sample is maintained in suspension 

and continuous motion, thus promoting better extract-· 

tion. Evaporati on of the solvent during boiling is 

largely prevented by a close fit of the extractor to 

the open end of the test tube. These features permit 

boiling for long periods without attention. When the 

extraction of the sample is completed, the heat is 

removed from the test tube and contents. As the tube 

cools, the contraction of the air remaining in the 

extractor causes the solution to flow through the 

filter into the extractor. Thus a filter extract is 

obtained by steps that are essentially automatic. 

The extractors may be used as filters for cold 

solutions by applying suction to the open end with a 

rubber ea.r syringe. 

Huff antibump test tube. The Huff (1951) antibump test tube shown m figure 4 is another device 

used to prevent bumping during the extraction 'Of a 

soil or rock sample with acid. With the round end 

of the test tube (13 by 100 mm) drawn to a point, 

Huff found that the extractant boils in the tip before 

the main mass becomes superheated~ thus preventing bumping. Heat can be applied by either a flame 

or a hot plate. 

Apparatus for preparation of metal-free water. 

Very pure water must be used in ttace analys1s 

because the quantity of a metal in the water used as 

solv.ent may exceed the quantity of metal in the 

sample. In the methods presented here the ratio 

of the weight of water used to the weight of sample 

is very great. For example, in the heavy metals 

5 

test described on page 13, the ratio of water to 

sample is 2200 to 1. In this method, if no precautions 

were taken to purify the water used, 0. 001 ppm of 

metal in the water would appear as 2. 2 ppm in the 

sample. Huff (1948) has reported 1. 52 ppm zinc, 

0. 01 ppm copper, and 0. 03 ppm lead in the tap water 

of the Denver, Colo. Public Supply. If such water 

were used in the.above test, the contamination would 

result in an error of 3, 300 ppm of zinc, 22 ppm of 

copper, and 66 ppm of lead. Obviously ordinary tap 

water should not be used. 

Several small resin demineralizers now commercially available are satisfactory for preparing 

metal-free water. However, since resin demineralizers remove only ionized impurities such as sodium, 

calcium, zinc, lead, sulfate, and bicarbonate, and · 

do not remove bacteria or organic impurities, water 

reasonably free of ·organic materials should be used, 

such as a public<water supply. 

Digestion and fusion rack. This piece of 

apparatus, shown in figure 5, is used to support 

eight test tubes over a gasoline stove. The rack 

consists of two disks of sheet steel 115 mm in 

diameter welded to a central supporting rod, 200·mm 

long. Each disk has eight holes for test tlJ.bes; the 

holes in the bottom disk are smaller, so that the 

test tubes cannot slip through, but large enough_ to 

permit the ready flow of heat. 

Fusion rack (used in Mo and W methods). This 

rack, designed to support three culture tubes at any 

desired angle over the .flame of a gasoline stove, is 

showri in figure 6. The design of the rack permits 

the operator to rotate as well as to raise and lower 

each tube independently. It consists of an iron band 

100 mm in diameter, 25 mm wide and 2 mm thick, 

three supporting rods with spring clamps pivoted at 

the upper ends, held in a vertical position in a slot 

through an "L" shaped member riveted to the outer 

side o.f the iron band. A set screw normal to the 

slot pe_rmits adjustment of height of the rods. 

Sieves. In the analysis of materials for trace 

constituents contamination must be kept to the minimum. 

Almost all the sieves currently available on the market 

are made of brass, and often solder has been used to 

fasten the screen. Sieves containing brass or solder 

cannot be used in preparin samples for determination 

o. traces o copper, zmc an ea • T e o owmg 

types have been used in our work: 

(a) Iron sieve. 2 mm mesh iron screen in an 

iron holder having an outside diameter of 

100 mm. 

(b) Aluminum sieve. 80 mesh silk bolting 

cloth in an aluminum holder with outside 

diameter of 100 mm. Stainless steel 

bolting c~oth has been used in place of the 

silk bolting cloth. It is stronger and 

prefe"rable if free of the constituents 

being determined. 

An aluminum receiver which fits both (a) and 

(b) is desirable. 

The sieve and sieve holder are shown in 

figure 7. 
Figure 2. --Kit containing two all glass chromographs. 

Figure. 3. --Stevens Extraction Stick. 
Toxicity of Reagents 

Most reagents used in analytical chemistry are 

poisonous. However, when the analyst is cautioned 

about the toxicitY of a specific reagent it is because 

of some special property of the reagent, . such aS' 

volatility, which makes handling the reagent especially 

hazardous. For example, potassium cyanide is 

extremely poisonous and reacts with acid to produce 

a volatile, lethal gas (HCN). Hydrofluoric acid is 

another example of a substance with a property 

which makes handling dangerous. If it is allowed to 

remain in contact with the skin more than two to 

three minutes, it produces an exceedingly painful 

burn, the pain persisting for two days or more. The 

vapors are also toxic. 

The reagents discussed below are mentioned 

especially because their use involv.es certain special 

hazards. 

Carbon tetrachloride. 

Carbon tetrachloride is one of the most toxic 

of the common .solvents. Carbon tetrachloride 

poisoning results in liver and kidney damage and 

may be fatal. Since the maximum allowable concentration in the air is 40 ppm (Elkins, 1950), carbon 

tetrachloride should never be used in a poorly ventilated 

room. If a large quantity of carbon tetrachloride is 

spilled, the windows should be opened and the room 

vacated until cleared of the fumes. The majority of 

fatalities have resulted from acute exposures while 

using the reagent as a cleaner in a confined space or 

from the products formed by pyrolysis of the reagent 

which may occur when fire extinguishers filled with 

carbon tetrachloride are used. 

Amyl alcohol 

Fatal poisonings from amyl alcohol have been 

reported. The harmful effects are ir;ritation and 

narcosis, but these are usually transitory. The 

maximum allowable concentration in the air is 50 ppm. 

If the precauUons listed for carbon .tetrachloride are 

applied in the use of amyl alcohol, no harmful effects 

are likely to result. One should remember, however, 

that amyl alcohol is inflammable. 

Isopropyl ether 

Very little is known regarding the toxic effects 

of isopropyl ether. It is reasonable to assume tha~ 

this ether is somewhat more toxic than diethyl ethe!t', 

but being less volatile is l.ess dangerous to use. Ifl 

the same precautions are followed as in the use of 

carbon tetrachloride, no harm should result. Like 

amyl alcohol, isopropyl ether is inflammable. , 

.I Potassium cyanide 

Potassium cyanide is exceedingly poisonous; 1 

a very smali amount taken internally is fatal. The:refore, never draw a potassium eyanide solution into 

a pipette by mouth; always wash 1mmed1ately after 

hand!mg potassmm cyamiie or 1ts soiuhons~ 

Acidification of cyanide produces a lethal gas 

(HCN). Never store potassium cyanide near acids ~ 

7 

Exercise meticulous care to avoid any possible 

contact of the salt or its solution with acids that 

may result from breakage in transport. Never add 

potassium cyanide solutions to an acid solutwn or 

acidify solutions contaming cyan1de. Always wash 

vessels thoroughly in which the reagent has been used. 

Hydrofluoric acid 

Almost all of the people likely to use the. methods 

in this compilation know of the vicious burns that 

result from contact with hydrofluoric acid, but may 

not be aware of the fact that the fumes are corrosive 

and poisonous. The generally accepted maximum 

allowable concentration for an s.:hr day is 3 ppm by 

volume in air. A concentration of 50 ppm or more 

may be fatal in 30 to 60 min. (See Manual Sheet 

H-10. Hydrofluoric acid-- aqueous and anhydrous--

handling and discharge of containers. Manufacturing 

Chemist's Association, Inc., Washington, D. C.) 

Therefore, a good draft away: from the operator is 

essential. Use in the field should be in the open 

with the operator on the windward side of the burner. 

Caution: An analyst using hydrofluoric acid should 

wash his hands frequently with copious amounts of 

water. 

Purification of Reagents 

Although special attention must always be given 

to purification of water used in trace anaiysis ( 11 Special 

Apparatus 11 ), reagent chemicals also must be checked 

for purity, and a high reagent blank avoided. Dithizone methods are particularly susceptible to error 

due to high reagent blanks. 

Solutions prepared from solid reagents are most 

conveniently purified by extraction with a carbon 

tetrachloride solution of dithizone. The procedure 

for this type of purification is to be found in the 

instructions for preparing specific reagents. The 

salts used in fusions (potassium bisulfate, sodium 

carbonate, sodium chloride, and potassium nitrate) 

are usually sufficiently pure to give satisfactory 

results, nevertheless, each batch should be checked 

by running a blank on the reagent. Fluxes giving a 

high reagent blank should be rejected, as purification is tedious. 

Hydrochloric and nitric acids are usually very 

low in heavy-metal content and frequently can be used 

without purification. If necessary, they may be 

purified by distillation from a pyrex still. Hydrofluoric · 

acid may be freed from lead according to the method 

of Rosenqvist (1942) as follows: 

Add 10 ml of 10 percent strontium chloride to 

one kilogram of concentrated hydrofluoric acid, allow 

the precipitate to settle, and aqain add 10 ml of 

strontium chloride solution. Allow the precipitate 

to settle and decant the supernatant liquid throuqh a 

filter paper in a hard rubber or plastic funnel. In 

this manner lead is removed from the acid by 

coprecipitation of lead .fluoride with strontium 

fluoride •. 

Pure ammonium hydroxide is easily obtained 

by saturatinq'metal-free water, cooled in an ice 

bath, with ammonia from a tank. The change in 
Figure 4. --Huff antibump test tube. 

Figure 5. --Digestion and fusion rack. 

8· 
·weight of the receiver indicates the concentration bf 

the solution. 

Carbon tetrachloride of reagent quality is usually 

satisfactory. Distillation in a pyrex still in the pr~sence of calcium oxide will give a product free of heavy 

metals. · 

METHODS OF ANALYSIS 

Explanatory Notes . I 

The plan is to present the minimum information 

required to perform properly each determination; :a 

brief introduction, a list of reagents and apparatu~, 

and .a concise statement of the procedure are given. 

While there are occasional warnings for critical 

operations, the purpose is to present direct instr uctions that can be followed by a relatively untrained 

operator. Those interested in the reactions involved, 

the interfering elements, and the comparative accuracy should refer to the original papers from whidh 

these methods were taken. 

In order to re·duce unnecessary repetition, a 

section on the preparation of the sample for analysis 

is inserted before the methods for soils and re>cksl. 

Subsequently it is assumed that a proper sample of 

soil, rock, or sediment has been prepared and therefore the directions for the analysis of such material 

start with a given weight of the finely ground sample. 

On the other hand, no consistent plan is followed in 

the preparation of samples of vegetation where the 

preparation of the sample is an integral part of each 

procedure. 

The aqueous solutions listed under "Reagents 

and apparatus" are identified by listing the solute 

and its approximate concentration in terms of percent, normality, or dilution; for example, sodium 

citrate, 50 percent, acetic acid, 2 N, or hydrochloric 

~cid, lt2. Detailed instructions for preparing splutions 

designated by percent or normality follow in each case. 

The designations 50 percent and 2 N do not imply exact 

·concentrations. The concentration expressed in terms of 

/ dilution, such as hydrochloric acid, 1+2, means that the 

reagent is prepared by mixing L volume of concentrated 

hydrochloric acid and 2 volumes of metal-free wat, r. 1 

Water used in the preparation of reagents, in 

dilutions and as a wash liquid, is metal-free water 

whether specified or not. The importance of metalfree water is disc.ussed under "Special Apparatus. " 

All of the apparatus required for each methbd is 

listed, but no consistent effort has been made to 

specify the amount of apparatus required to work 

efficiently since the size of the job to be done and . 

the facilities available are the determining factors. 

However, lists of reagents required for 1, 000 de,terminations with each method are given as an appendix. 

Determination of Heayx Metals in J(ater: . I 

A complete description of the in~thod and itl 

applications are given by Huff (1948). According! to 

Huff, the sensitivity of .the test permits the detection 

of 0. 002 ppm of zinc, 0. 01 ppm of lead. and 0. Ollppm 

of copper in a 50 ml sample. Waters high in heavy 

metals can be analyzed by reducing the size of the 

sample taken for analysis. Organic matter in the 

water tends to ca:use stable emulsions to form 

between the carbon tetrachloride and water. These 

emulsions and zinc contamination are the most 

serious interferences encountered in the use of the 

method. Although reagents of exceptional purity 

are required, only simple equipment is needed and 

the test can be made in a few minutes in the field • 

Thus the geologist can test water samples as he 

collects them and f0llow leads without delay. 

Reagents and apparatus 

Acetic acid 2 N, dilute ll4 ml of glacial acetic 

acid to lliter with metal-free water. · 

Acetic acid 1 N, dilute 50 ml of 2 N acetic acid 

to 100 ml with metal-free water. 

Sodium acetate 2 N, dissolve 164 g CH3COONa 

in metal-free water and dilute to 1 liter 

Acetate buffer, Mix nine parts 2 N sodium 

acetate with one part 2 N acetic acid. Purify by 

shaking with successive portions of 0. 016 percent 

dithizone solution until the organic layer remains 

green. 

Ammonium hydroxide 2 N, dilute 127 ml concentrated N~OH 1 liter with metal-free water. 

Dithizone (diphenylthiocarbazone), 0. 016 

percent weight per volume. Dissolve 0. 08 g of 

dithizone in 500 ml of reagent-grade carbon tetrachloride. Since sunlight and heat decomposes the 

reagent, solutions should be stored in paper-wrapped, 

glass-stoppered, pyrex bottles and kept cool. 

Dithizone, 0. 0016 percent Vll'eight per volume. 

Dilute 10 rrtl of 0. 016 percent. dithizone solution to 

100 ml with reagent-grade carbon t~trachloride. 

When working at temperatures over 70F, . prepare a 

fresh solution every 4 hr. 

Potassium cyanide, 1 percent. Dissolve 1 g 

KCN .in 2 ml water. Add 2 drops of 0.016 percent 

dithizohe solution. Extract excess dithizone from 

potassium cyanide solution with small portions of 

chloroform until no green dithizone appears in the 

chloroform phase. Dilute to 100 ml with metal-free 

water. Shake with carbon tetrachloride and discard 

the organic layer. Caution: Y!f£:1. poisonous! 

See "Toxicity of Reagents. " 

Sodium thiosulfate 2 N. Dissolve 25 g of 

Na2S203. 5H~O in metal-free water an:d dilute to 

100 ml. Purify by shaking with successive portions 

of 0. 016 percent dithizone · solution. 

Metal-free water. Pass tap water through a 

resin demineralizer. See "Special Apparatus." 

Zinc standard, 0. 01 percent in 0. 1 N HCl. 

Dissolve 0. 01 g of reagent-grade zinc in 100 ml of 

0. lN HCl. One ml of this solution contains 

100 micrograms of zinc. Less concentrated standard solutions· are prepared by dilution. 
Figure 6. --Fusion rack. 

Figure 7. --Aluminum sieve and hoider. 

10 
Thymol blue indicator 0.04 percent. Dissolve 

0. 04 g of the sodium salt in 100 ml water. 

4 graduated cylinders, 100 ml, glass-stoppelred, 

pyrex. 

1 graduated cylinder, 5 ml, pyrex. 

1 separatory funnel, 125 ml, Squibb type, glassstoppered, pyrex. 

6 dropping bottles, 30 ml, flat top. I 

pH meter, Beckman Model G, or suitable 

indicator papers for determining acidity of water I 

samples. 

Procedure •, . · I 

Transfer 50 ml of·the water sample to a 100J·m1 

glass-stoppered, graduated cylinder. Add 5 dropf of 

the buffer solution, 5. 0 ml of 0. 0016 percent dithizone solution C~,nd shake vigorously for 1 min. If 

the color of ~he dithizone solution is red after the 

initial shaking, tleari' the cylinder·and repeat the 

analysis using a sma'ller volurne of sample. Repeat 

i.mtil a mixed . color. . (red metal.:.dithizonate plus· · 

unreacted green dithizone.) is obtained; determine 

quantity ·of heavy. metals present · expressed as Zn 

by reference to table 2, column 3. 

If the dithizone remains apparently. unchanged 

add 2 drops of thymol blue indicator, ammonium 

hydroxide until the indicator changes from yellow to 

blue, then 1 additional drop of ammonium hydroxide; Shake again for ·15 sec~ _Estimate visually 

by referring to table. 2, column 3, mono-color range 

pH about ·g. 

Table 2.--Description of colors with heav1 metals test on standard solutions (according to Huff) 

I 

Acidity of Micrograms Col6r of dithizonate in strong, white transmitted light* 

extraction of metal in 

50 ml Zinc Copper Lead 1:1:1 mixture 

solution of Zn, Cu, _Pb 

Mixed color range; 20 Light purplish 

pH of about 5.5 red 

obtained with 15 Light red Light purplis 

acetate buffer. Strong purplish purple red 

10 Light purplish red Pale purplish 

red blue 

7 

5 I Pale purple Light blue Light red 

Light /red 

green purple 

4 Pale purplish 

purple blue 

3 Light jpurple Light blue Pale blue 

green 

2 Pale blue light bluish Light bluish Light blue 

green green green 

1 Light blue Light green Light bluish 

1/2 

green 

Light fbluish 

green 

green 

' . 0 Light green Light green Light green Light green 

I 

Mono-color range; 1 Strong pink Moderate pink Moderate pink Strong pink · pH of about- 9.0 · 1/2 Weak pink Faintest color Faintest color Weak pink 

obtained by detectable detectable 

adding ammoniUm 1/10 Faintest color Colorless Colorless Faintest colo 

hydroxide to deteytable dete.ctable 

mixed color test. 0 Colorless Colorless Colorless Colorless 

*Color identification based upon Munsell notation . . See Munsell Book of Color, Standard Edition, 

Munsell Color Co., Inc., Baltimore, Md., . 1929, and Judd, D. B. and Kelly, K. L;, Method of 

designating colot:>s, National Bureau StanclB.rds Research Paper 1239, Sept., 1939. It may be 

noticed that in the mixed color range the l colors all have about the same · value .but vary in h~e 

and chroma, the intenned~ate hues being cij.stin.ctly grayish while the end m.embers 1have strong 

chroma; in the .mono-color range the hue remains constant while the •Chroma anc;l value change as the colors become fainter. 

Because the reagent is very sensitive, the 

analysis is extra-ordinarily susceptible to con- 1 tamination; it is advisable to keep all apparatus 

scrupulously clean and always make check determinations. 

In the course of prospecting it may be desi'l able 

to identify the metal or metals producing the 

11 

positive tests. The supplemental tests, the procedures of which are given in table 3, permit 

the separation of copper, lead, and zinc; other 

metals may cause interference, but it is likely 

that many of these occur only in very small 

amounts in natural waters. 

n 

r 
Table 3.--Supplemental determinations for heavy metals in water (according to Huff) 

Metals 

Copper 

group 

Zinc 

group 

Producedure 

Repeat as in the general test with 

the same volume of sample but using 

1 ml of 1.0 .N acetic · acid instead of 

the acetate buffer. A mixed color 

after shaking indicates presence of 

the copper group. Add more sample 

and shake to change all dithizone to 

metal dithizonates. 

Repeat the test as before adding 

both buffer and 5 ml of 2.0 N purified sodium thiosulfate solution. 

Significance of color 

Copper-Purplish red 

Silver--Yellow 

Mercury--Orange (I) to orange yellow (II) Bismuth--Oran~ yellow Gold--Yellow (floes) Palladium~-Dark violet 

.. 

Platinum (II) --Green carbon tetrachloride 

layer; violet or violet-red agueous layer 

Thallium (III)--Yellowish red (reaction not 

complete) . . 

Zinc--Red 

A mixed color after shaking indicates 

presence of the zinc group. Add more sample . and shake to change all di thizone 

to metal dithizonates. 

Tin (II)--Red (not stable) 

Palladium--Dark violet (reaction slow) 

Cadmium--Red (pH of 8 or over) 

Lead 

group 

Repeat the test as before, after adding · 5 drops of 2. 0 N ammonium hydroxide 

followed by 1 ml of a 1 percent 

purified potassium cyanide solution 

instead of the buffer. Any color left 

after shaking, other than a pale yellow 

dithizone oxidation product, indicates 

presence of the lead group. Oxidation ·of the dithizone ·can be decreased 

by preliminary addition of a little 

hydroxylamine hydrochloride. 

Other 

metals 

Detectable with simple field .test but 

removed by any of the procedures given 

above. Must be isolated by other 

methods. 

Preparation of soils and rocks 

for analysis · 

Simplicity in all steps of the analysis is 

required for rapid tests. As these chemical methods 

are only moderately accurate, large samples and 

elaborate sample preparation are not justified. Any 

si~plification of the sampling procedure that will 

provide a small satisfactory sample is desirable. 

In any' particular area the minimum size of 

sample required to give satisfactory results should 

be determined experimentally. An example of this 

is found in the work of Hawkes and Lakin {1949) in 

Tennessee. They collected a series of bulk samples 

{about 500 g) and compared the analyses of these 

with those of grab samples {about 5 g). The results 

showed that 5 g samples were just as satisfactory as 

samples 100 times larger. Another type of a 

simplified sampling procedure was usecl by Lovering 

and others {1950). These workers demonstrated that 

dry sieving of soil and alluvium samples through an 

80-mesh sieve gave satisfactory subsamples for the 

study of the dispersion of copper from the San Manuel 

copper deposit. This procedure greatly reduces the 

size of the sample and eliminates the need for 

grinding. 

When no modification in sampling can be 

employed to reduce the sample size, the following 

12 

Lead--Red 

Tin (II~-:-Red (optimum pH 6-9; not stable) 

Bismuth--Orange red 

Thallium (I)--Red (pH of 9 or over) 

Cobalt--Violet (optimum pH 7-9) Nickel--Brown (weakly basic solution) 

Iron (II)--Violet red (fH 6-7 only) 

Manganese--Brown floes pH about 11) 

Indium--Bed (optimum pH 5-6) 

Thallium (III)--Yellowish red (pH 3-4 only) 

general procedures are recommended for the 

preparation of the sample. 

Soils. --Dry the sample, break up clods 

with a wood rolling pin and pass the sample 

through a 2 mm mesh sieve. Pour the sieved 

soil in a pile on heavy wrapping paper, mix 

thoroughly, quarter, discard opposite quarters, 

and repeat the process until a sample of 3 to 5 g 

remains. Pulverize this small subsample 

in a mullite mortar to an impalpable powder. 

From this powderea sample take the amount 

required for the analysis. 

Rocks. --Break the rock fragments into 

small chips with a Plattner diamond mortar, 

and pass the sample through a 2 mm mesh 

sieve, crushing the portion that fails to pass 

the sieve until the entire sample has passed 

through the coarse sieve. Mix thoroughly 

and quarter down as in soils to a subsample 

of 3 to 5 g. Pulverize this small sample in a 

mullite mortar to an impalpable powder for 

analysis. 

Determination of HeaVy Metals in 

soli or sedlment 

Huff (1951) has described this procedure, and 

has discussed the reactions involved in the method 

as well as its usefulness in geochemical prospecting. 
The test is designed to detect as little as 50 ppm 

and as much as 10,000 ppm of heavy metals expressed 

as zinc equivalents. The test is most sensitive· for . 

zinc and least sensitive for lead. Four methods of 

preparing the sample solution are described in orqer 

of increasing rigor of attack on the sample. If representative samples are treated by all four digesUon · 

methods, the digestion method best suited for a_ .. 

particular study can be selected; in _general, it wi~l 

be the quickest method which gives satisfactory · 

results. The test is easy to make and only simple 

apparatus and reagent-grade chemicals are required 

to make 60 to 80 tests per rpan day in a make-shi]t 

field laboratory. The test has been used in reconnaissance studies. 

Reagents and apparatus 

Dithizone (diphenylthiocarbazone), 0. 016 perrerit 

w~ightper volume. DissolveO. 08 g of dithizone in 500 ml of 

reagent-grade carbon tetrachloride. Since sunlight 

and heat decompose the reagent, solutions should be 

stored in paper -w:r:apped, glass -stoppered, pyrex 

bottles and kept cool. 

Dithizone , 0. 0016 ·percent weight per volume. 

Dilute lO ml of 0. 0161 percent dithizone solution to 

100 ml with reagent-grade carbon tetrachloride. 

When working at temperatures over 70F, prepare a 

fresh solution every 4 hr. 

Water. Pass tap water through-resin demineralizer.--see"Special Apparatus." ·

1 

Concentrated nitric acid, approximately 69 percent (constant-boilmg). Purify by' distilling in an allpyrex still. 

Dilute nitric acid, 1+ 7. 1· 

Hydrofluoric acidt approximately 48 percen~. 

A. C. S. analyzed grade. 

Sodium acetate, 25 percent. Dissolve 250 g of 

anhydrous sodium . acetate, or 415gof NaC2H3o2. 3H2o, 

in water; and purify by shaking ·in a large separatory 

funnel with dithizone stock solution. Remove traces 

of dithizone by shaking with pure carbon tetrachloride. 

Dilute to 1. 0 liter. 1 

Ammonium flt:.oride , 10 percent. Prepare by 

dissolving 100 g of ammonium fluoride in water; 

purify as with sodium acetate, and. dilute to' l. 0 liter. 

Keep in a pyrex bottle. 

Buffer solution, containing 5 percent sodium 

acetate and 1 percent ammonium fluoride. Prepare 

as needed by diluting 200 ml of 25 percent sodium 

acetate solution and 100 ml of 10' percent ammonium 

fluoride solution to 1. 0 liter. 

Standard zinc solution, 0. 01 percent in 

approximately 0.1 N hydrochloric acid. Dissolve 

. r~agent-~ade zinc in a slight excess of hydrochloric 

acid and dilute to volume. Before use, dilute with pure 

water and a little additional acid to a 0. 001 percent 

solution (10 micrograms of zinc per ml). • 

Huff antibump tubes. See "Special Apparatus." 

13 

Digestion tube rack.·.: The dige·stion tubes can 

be held conveniently in a ~ooden frame having a series 

of 13-mrp. hol~s spa~ed withce~ters abo.ut an inch 

apart. ·. . . · 

l pipette, 0. 1 ml, grad~e , in hundredths of 

a ml. ~ .... , .. ' ; 

Luc.ite spoon, a luc,ite,t:~ar with a cavity.of 0. 25 

ml,- · 7 .mm diameter, _6. 5 _mm deep, drHled near 

one· end. 

l graduated cylinder, 100 ml, glass-stoppered, . 

pyrex. 

l beaker, 250 ml. 

3 graduated cy~inders, 5 ml,. pyrex. 

separatory funnel, . 125 ml. 

.serological pipette, 10 ml, graduated in 

tenths of a ml. 

l :serological pipette, 5 ml, graduated in tenths 

of a ml. 

l alcohol lamp, small. 

1 hot plate, electrical, 116 volt a-c, variable 

temperature control heating surface· '6 by 6 in. 

12 platinum dishes, flat-bottomed dishes, with~ 

out rim, about 20 mm in diameter and 10. mm high~ 

1 platinum wire, 75 mm long. 

1 polyethylene wash-bottle, 250 ml. 

Colorimetric tubes. 25 by 200 mm glass 

culture tubes, with a screw cap. ·Mark the tubes 

with a stylus at volumes of 5, 10, 20, and 40 ml. 

Glass-stoppered, graduated pyrex cylinders are a 

satisfactory substitute for the colorimetric tubes. 

Procedure 

Digestion: Four· different digestion methods 

are described below which represent four distinct 

steps of increasing rigor of digestion. By the use 

of all four digestion methods on representative 

samples the digestion method best suited for use for 

a particular study can be selected; in general, the 

best method will be the quickest method that gives 

satisfactory results. Instructions for the di~estions 

are as follows: 

A. Place a scoopful. of the ground sample 

in an antibump tube, add 4 ml of dilute nitric 

acid and heat over an alcohol lamp. Maintain 

at or near the boiling point for 10 min. 

B~ Place a scoopful of the ground sample 

in an antibump tube, add 4. 0 ml of dilute ni:tric 

acid and boil slowly and contin~ously on a hot 

plate for 1 hr. . Dilute with water to 4. 0 ml 

~nd mix by shaking~ _ 

. ·c: Place'; a scoopful of the ground sample 

·in an antibump tube, add 1 ml concentrated 
nitric acid, and heat on a hot plate {low heat) 

overnight without boiling; heat further the 

following . morning. {high heat) until about onehalf the acid is boiled away. Dilute to 4. 0 ml 

and mix by shaking. 

D. Place a scoopful of sample in a 5 ml 

platinum dish, add 2 ml hydrofluoric acid and 

2 ml concentrated nitric acid, mix with a platinum rod. Heat on a hot plate at about 35 C to 

40 C until dry. Cool and add 2 to 5 drops of 

concentrated nitric acid, _ heat to dryness again. 

Add 10 drops of concentrated nitric acid and 10 

drops of water and heat. Wash the contents 

into a tube with water and dilute to 4 ml. 

Each of the four digestion methods leaves the 

sample dissolved in nitric acid of about the same 

concentration. When the sample solution cools, · the -

solid residue settles to the bottom of the digestion 

tube, leaving a clear yellowish solution. Aliquots of 

this are pipetted for the estimation. 

Estimation.--Place 5. 0 ml of the dilute dithizone 

solution in a clean colorimetric tube, add 35 ml of the 

buffer solution, 0. 2 ml of the sample solution, and 

shake for 30 sec. Compare the color of the carbon 

tetrachloride layer with the color of similar layers 

prepared by using zinc standards or with the colors 

listed in table 3 to determine the metal content of the 

sample (expressed as zinc eqUivalents, that is zinc 

plus one-half copper plus one-fourth lead). If the 

carbon tetrachloride layer is red or nearly red, clean 

the tube, using distilled water and dithizone solution. 

Repeat the determination using a smaller aliquot of 

the sample solution to obtain a mixed color (red metal 

dithizonate plus unreacted green dithizone), so that 

the concentration can be read from table 4. ·The 

color differences are most sensitive near the purplish, 

midpoint of the range, and this range should be used 

for greatest ac~uracy. . 

Do not use more than 0. 2 ml of the sample 

solution for the determination. The procedure is 

designed so that samples containing 50 or 100 ppm 

total heavy metal, a normal background concentration, 

will give a slight positive test and·any concentrations 

higher than this background will be easily distingUishable. The test, as described, is not sUitable for determining heavy-metal contents in the range below 50 

to 100 ppm, the normal background range. It is 

advisable to make many repeat determinations and 

to run blanks on the reagents frequently to avoid error 

by contamination. If any check determinations are 

to be omitted, omit those for '

1background11 samples. 

Determination of Zinc in Soils 

The field method for zinc in soils and rocks 

given below is described more fully by Lakin, Stevens, 

and Almond (1949). In the authors' experience about 

85 percent of the values obtained by the field method 

are within :t. 40 percent of those obtained by careful 

laboratory analysis. The method, as described, is 

applicable to samples containing 50 to 1000 ppm of 

zinc. Under the conditions of the . test, the reaction 

of copper with dithizone is largely prevented. However, if the copper content of a sample is ten times · 

that of zinc, the zinc value may be as much as · 

14 

75 percent greater than its true value. Care must be 

exercised to avoid contamination, since erratic 

results are often due to zinc contamination of the 

test tubes, pipettes, or reagent solutions. Under 

favorable conditions up to 60 determinations per man 

day can be made. The apparatus is simple and portable. The chemicals required for the test are readily 

available and, except for carbon tetrachloride, are 

not hazardous. The method has been used widely in 

geochemiCal prospecting. 

Reagents and apparatus 

Potassium bisulfate. Analytical grade ground 

to fine powder in a porcelain mortar. 

Water. Pass tap water through a resin 

demineralizer. See "Special Apparatus." 

Sodium acetate, 2 N. Dissolve 164 g CH3COONa· 

and dilute to 1 liter with metal-free water. · 

Acetic acid, 2 N. Dilute ll4 ml of glacial acetic 

acid to lliter with metal-free water. 

Acetate buffer. Mix 5 volumes of 2 N sodium 

acetate wit}). 2 volumes of 2 N acetic acid, and remove 

reacting heavy metals by shaking with 0. Ol percent 

dithizone solution. 

Dithizone solution, 0. Ol percent weight per 

volume. Dissolve 0. 01 g in 100 ml of reagent-grade 

carbon tetrachloride. Store in cool, dark place. 

Dithizone solution, 0. 0025 percent weight per 

volume. Dilute 25 ml of 0. Ol percent solution to 100 

ml with reagent-grade carbon tetrachloride. 

Sodium thiosulfate. Dissolve 50 g of Na2S203. 

5H20 in 100 ml of water. Remove reacting heavy 

metals by shaking with 0. 01 percent dithizone 

solution. 

Standard zinc solution. 0. Ol percent in about 

0.1 N hydrochloric acid. Dissolve 0.1 g reagentgrade 30-mesh zinc in concentrated hydrochloric acid 

and dilute to 1 liter. One ml of this solution contains 

100 micrograms of zinc. Prepare dilute solution 

containing 20 micrograms per ml from the standard 

solution. 

20 pyrex culture tubes, 18 by 150 mm, marked 

at 3, 10, and 11 ml. 

20 pyrex culture tubes, 16 by 150 mm, marked 

at 5 ml. 

1 serological pipette, 5 ml, fitted with stopcock 

at upper end. 

1 graduated cylinder, 100 ml, or other suitable 

device in which to support pipette. 

Lucite t3poon, a lucite bar with. cavity of 0. 05 

ml, 4 mm diameter, 4 mm deep, drilled· near one 

end. 

Lucite spoon, a lucite bar with cavity of 0. 25 

. ml, 7 mm d1ameter, 6. 6 mm deep, drilled near· one end. 
....... 

01 

Table 4.--Descriptive chart of color · of dithizone solution for determination of heavy metals, expressed as zinc 

equivalents according to Huff 

Aliquot Volume Green Blue green Blue Purple Red purple Purflish red Red 

(ml) dithizone (ppn) (ppn) (ppn) (ppn) (ppm} ppm) (ppm) solution 

0.2 5 0 50 100 150 200 ~50 300, or more 

.2 5 0 100 200 300 400 500 600 or more 

.05 5 0 200 400 6oo Boo 1,000 1.200 or more 

.025 5 0 400 Boo 1,200 1,600 2,000 2,500 or more , 

.0125 ~ 0 Boo 1,600 2,500 3,500 4,000 5,000 or more 

.0125 10 0 l,Boo 3,500 5,000 7,000 9,000 10,000 or more 
Mullite mortar and pestle, outside diameter of 

mortar, 75 mm. 

2 sieves, 2 mm mesh iron screen and 100 mesh 

cloth, see "Special Apparatus." 

1 camel's-hair brush, length of brush ~ part, . 

18 mm. 

1 small spatula, zinc free, length of blade, 

50 mm. 

! ,digestion and fusion rack. See "Special 

Apparatus. " 

1 gasoline stove. 

Procedure 

Preparation of Sample Solution. --Fill a lucite 

. spoon, capacity 0. 05 ml, with soil by tightly pressing 

the prepared soil into the spoon with a small flexible 

spatula. Wipe the outside of the spoon level with the 

spatula, and tap into a pyrex {18 by 150 mm) culture 

tube. Add one spoonful (0. 25 ml) of powdered 

potassium bisulfate to the soil sample and place in 

the digestion and fusion rack. Place the rack with 

seven test tubes containing soils and one reagent blank 

on the gasoline stove and heat for about 10 min or 

until the soil is essentially decomposed . . If necessary, 

add a little more potassium bisulfate to effect the 

desired fusion. Remove, allow to cool, add 3 ml of 

water to each sample, and heat again until a milky 

suspension is obtained. Prolonged or too violent 

heating will cause excessive bumping and should be 

avoided •. Add 7 ml of the acetate buffer solution and 

1 ml of the sodium thiosulfate solution to each sample, 

stopper with a clean cork, shake thoroughly, and set 

aside to allow the suspension to settle and the solution to cool. 

Estimation. --This step is essentially a titration. Place 5 ml of the 0. 0025 percent dithizone 

solution in a pyrex culture tube (16 by 150 mm). Add 

measured volumes (1. 0, 1. 5, 2. 0, 3. 0, and 8. 0 ml) 

of the solution prepared from a soil sample to the 

dithizone solution and shake vigorously for 1 min 

between each addition, using a clean cork to close 

the test tube. Sufficient sample solution has been 

added when the color of the carbon tetrachloride layer 

matches a standard containing 5 micrograms of zinc, 

prepared as follows: Add 20 micrograms of zinc to 

the reagent blank carried through the fusion process, 

dissolve and buffer as above, and shake one-fourth · 

of the solution with 5 ml of 0. 0025 percent dithizone 

solution. Make new color standards every 30 min 

because the color fades rapidly. 

The added increments of the sample solution · 

correspond to zinc content of the soil samples as follows: -

Milliliter of sample solution 

required to match 

standard 

Probable zinc content 

(ppn) Reported group value 

(ppn) 

1.0 ---------------- 1.5 ---------~------

2.0 ---------------- 3.0 to 8.0 ------------- excess of 8.0 ml ---------

1000 and up 700 - 1000 . 400 - 700 

100 - 400 

under 100 

1000+ Boo 

500 

300 

100 

Chromographic Determination of Nickel 

in Soils and Rocks 

This field method for the determination of 

nickel in soils and rocks, together with an 

illustration of its use, is given by Stevens 

and Lakin -(1949). The method may be used without 

modification on samples ranging from .30 to 2000 ppm 

in nickel content. In the authors' experience about 

85 percent of the results are within + 40 percent of 

those obtained by spectrophotometric analysis. A 

strip of dimethylglyoxime reagent paper is inserted 

in .. the chromograph and the sample solution allowed 

to filter through the paper at a controlled rate. Nickel 

in the test solution reacts with the dimethylglyoxime 

in the paper to form a red precipitate, the intensity 

of the color being a function of the quantity of the 

metal present. Copper and cobalt also react under 

the conditions of the test to give water-soluble complex compounds and relatively large amounts may 

interfere by removing the reagent from the paper. 

The method is easy to perform and with adequate 

equipment, 40 or more determinations can be made . 

per man day. To work effectively, four to six 

18 

chromographs should be provided. The confined , 

spots obtained by the method serve as semipermanent 

records of the tests performed. The method is suitable for rapid analysis of large numbers of samples 

where a high degree of accuracy is not needed. 

Reagents and apparatus 

Potassium Bisulfate. Analytical quality is 

satisfactory provided the same lot is used to make 

the standard series. Pulverize before using. 

Sodium citrate solution, 13. 3 percent. Dissolve 

133 gin 500 ml of metal-free water and dilute to one liter. 

Ammonium hydroxide, concentrated C. P. grade. 

Litmus paper, red. 

Water. Pass tap water through resin demineralizer. · See "Special Apparatus." 

Dimethylglyoxime solution, 2 percent. Dissolve 

2 q of dimethylglyoxime in lOO ml of acetone. Pre-

_pare as needed. 
Reagents and apparatus 

Potassium Bisulfate. Analytical quality is 

satisfactory pro-vided the same lot is used to make 

the standard series. :pulverize before using. 

Sodium citrate solution, 13. 3 percent. Dissolve 

·133 gin 500 ml of metal-free water and dilute to one 

liter. 

Ammonium hydroxide, concentrated C. P. grade. 

Litmus paper, red. 

Water. Pass tap water through res5n demineralizer. See "Special Apparatus~" 

Dimethylglyoxime solution, 2 percent. Dissolve 

2 g of dimethylglyoxime ip 100 ml of acetone. Prepare 

as needed. 

Dimeth 1 1 oxime Rea ent Pa er. Dip sheets 

of no. Whatman filter paper into a percent solution of dimethylglyoxime in acetone at a rate faster 

than the spread of solvent through the paper. Pauses 

must be avoided, as they cause uneven distribution of 

the reagent on the paper by allowing the so1vent to 

spread through the paper without the reagent. When 

the paper is dry, repeat the process. Discard the 

outer edges of the paper and cut the dry reagent paper 

into strips 7/16 in wide. The reagent paper is stable 

for several months. For more detail on . preparation 

of reagent papers, see Clarke and Hermance (1938). 

Chromograph. See "Special Apparatus. " 

Balance. Torsion, capacity 120 g, sensitivity 

2 mg. 

Gasoline stove. 

Lucite spoon. A lucite· bar with cavity of 

0. 50 ml (10 mm diameter, 6. 5 mm deep) drilled near 

one end. 

Culture tubes. Borosilicate glass, 18 by 150 mm, 

marked at 2. 5, 3. 0, and 5 ml. 

1 pipette, 0. 5 ml, graduated in tenths of a ml. 

Filter paper, Whatman no. 50, Large sheets, 

50 em diameter. 

Ear syringes, adult size. 

Stevens Extraction Sticks. See "Special 

Apparatus." 

Standard nickel solution, 0. 01 percent. Dissolve 

0. 01 g of pure nickel in 10 . ml of 6 N nitric acid. 

Dilute to 100 ml .with water. 

Preparation of standard spots 

The colors obtained on the confined spots are 

affected by the presence in the solution of modifier 

ions such as iron and aluminum. It is therefore necessary to prepare the standard spots used for comparison from solutions that contain the ions that will 

be present in the unlmown solutions to be analyzed. 

17 

Soil solution. --Fuse in a pyrex beaker 7 g of 

soil, selected for exceedingly low nickel content, with 

35 g of potassium bisulfate. Cool, add 27 g of sodium 

citrate and 100 ml of metal-free water, and digest on 

a steam bath until the cake is disintegrated. Cool, 

dilute to 200 ml, and filter through Whatman no. 50 

filter paper. 

Standard nickel test solutions. --Prepare a 

series of standard nickel test solutions by adding 

appropriate voll,lmes of a standard solution of nickel 

from a microburette to 3 ml of the soil solution: Add 

ammonium hydroxide until a piece of litmus paper in 

the solution turns blue. Dilute to 5 ml. The series 

of nickel test solutions should vary from 0. 30 microgramsNi/ml (corresponding to 15 ppm Ni in 0, 1 g 

of soil sample) to 40 micrograms Ni/ml (corresponding to 2, 000 ppm Ni). 

Make confined spot tests with 0. 2 ml of each of 

the standard test solutions, using dirnethylglyoxime 

reagent paper. Mount the series of spots on the edge 

of a cardboard chart and cover with cellophane tape. 

Label each spot with the figure of parts per million 

of nickel to which it corresponds. Prepare new 

standards with each new batch of reagent paper. 

Procedure 

Preparation of sample solution. --Fuse 0. 1 g of 

soil with 0. 5 g (or one 0. 5 ml lucite spoonful) of 

potassium bisulfate in a culture tube until a dull-red 

quiescent melt 'is obtained. As the tube cools, rotate 

to allow the molten meterial to crystallize in a thin 

layer on the walls of the tube. To the cooled tube 

add 3 ml of 13. 3 percent sodium citrate solution and 

boil until ·the melt disintegrates. Cool, add concentrated ammonium hydroxide until a piece of litmus 

paper in the solution turns blue, and dilute to 5 ml 

with water. Place a Stevens Extraction Stick in the 

test tube containing the sample solution, insert a 

deflated rubber ear syringe into the top of the extraction stick and allow to stand until a sufficiently large 

aliquot has filtered. 

Determination of nickel. --Place a strip of 

dimethylglyoxime reagent paper in the reagent-paper 

slot of a chromograph. With the stopcock turned to 

connect the adjustor bulb with the connector tube, 

press the rubber adjustor bulb to force the water up 

the tube to the upper timing mark, then close the 

stopcock. Tighten the metal coupling to press the 

glass pipe filter head firmly against the reagent paper. 

Place 0. 2 ml of the filtered sample solution in the 

bottom of the filter head. Turn the stopcock to join 

the connector tube with the medium capillary. When 

all of the solution has drained through the reagent 

paper, turn the stopcock to join the 9;djustor bulb to 

the connector tube. Raise the filter head sufficiently 

high so that it is well clear of the reagent paper. 

Draw the reagentt..paper strip through the reagentpaper slot until the spot is clear of the filter head, 

·and write the sample number on the reagent paper 

adjacent to the spot. Readjust the liquid column to 

thelevel of the upper timing mark and proceed as 

before with the next sample solution. When the spots 

are dry, compare them with standard spots on the 

chart. 

Storage of test spots. --Place the strip of rea- gent paper containing the test spots, when they are 
dry, on a slightly longer piece of cellophane tape, 

with spots face down against the adhesive, and mount 

the strip on a .page of the notebook. Spots stored in 

this way have undergone no apparent changes in more 

than 2 yr. 

Chromographic Determination of Copper 

in Soils and Rocks 

This method is described by Stevens and Lakin 

(1949). It is another example of the confined spot 

technique in which the chromograph is used. (See 

"Special Apparatus.") Two sources of error inherent 

in the method tend to give low results. These are the 

incomplete . attack of the sample by the bisulfate fusion 

and oc.casional excessive precipitation of alums from 

the aqueous solution of the fusion. Nevertheless the 

method gives satisfactory results on soil and rock 

samples ranging from 10 to 1500 ppm in copper content. Forty or more determinations can be made per 

man day and the results are usually well within 2:. 40 

percent of those obtained by spectrophotometric . 

methods. It is useful for the rapid analysis of large 

numbers of samples provided that great accuracy is 

not required. It has been used in geochemical 

prospecting. 

R.eagents and apparatus 

Potassium bisulfate. See "Determination of 

Nickel." 

Sodium citrate solution, 13. 3 percent. Dissolve 

133 gin 500 ml of metal-free water and dilute to 

1 liter. 

Ammonium hydroxide, concentrated C. P. grade. 

Litmus paper, red. 

Acetic acid, 50 percent. Dilute 25 ml of C. P. 

glacial acetic acid to 50 ml with metal-free water. 

Water. Pass tap water through resin demineralize;:-- See "Special Apparatus." 

R.ubeanic acid dithiooxamide) 2 percent. 

Dissolve g of rubeanic acid in 0 ml of acetone. 

Prepare as needed. 

Rubeanic acid reagent paper. Dip sheets of 

no. 50 Whatman filter paper into a 2 percent solution 

of rubeanic acid in acetone at a rate faster than the 

spread of solvent through the paper, to prevent uneven 

distribution of the reagent on the paper. Remove, blot 

between clean sheets of blotting paper, and allow to 

dry. Repeat the process. Discard the outer edges of 

the paper, and cut the dry reagent paper· into strips 

7/16 in. wide. Use care in handling the reagent 

paper since the amount of copper on one's fingers is 

usually. sufficient to react with the rubeanic acid on 

the reagent paper and produce a black print of copper 

rubeanate. The reagent paper is stable for several 

months. For more detail on preparation of reagent 

papers, see Clarke and Hermance (1938). 

Standard copper solution, 0. 01 percent, Dissolve 

0. 2 g of clear uneffloresced crystals of C uS04. 5H 20 

in water, add enough sulfuric acid to make the final 

acidity about 0. 1 and dilute to 500 ml. One ml of 

this solution contains 100 micrograms. 

18 

Apparatus. --Identical to that used for 

determination of nickel. 

Preparation of standard spots 

The color obtained on the confined spot with 

rubeanic acid is suppressed by the presence of modifier ions ·in the solution such as iron .and aluminum. 

It is therefore necessary to prepare the standard spots 

used for comparison from solutions that contain the 

ions that will be present in the unknown solutions to 

be analyzed. 

Soil solution. --Follow exactly the same procedure as in nickel method, using a soil exceedingly 

low in copper content. 

Standard copper test solutions. --Prepare a 

series of standard copper te.st solutions by adding 

appropriate volumes of a standard solution of copper 

from a microburette to 3 ml of the soil solution. Add 

ammonium hydroxide until a piece of litmus paper in 

the solution turns blue. Dilute to 5 ml with metalfree water and add one ml of 50 percent acetic acid. 

The series of copper test solutions vary from 0. 167 

micrograms of Cu/ml (corresponding to 10 ppm Cu in 

0.1 g of soil) to 25 micrograms of Cu/ml (corresponding to 1500 ppm Cu in 0. 1 g of soil ). The copper 

content of the standard test solution series should be 

made so that successive standards differ by about 

30 percent. 

Make confined spot tests with 0. 2 ml of each 

of the standard test solutions, using rubeanic acid 

reagent paper. Mount the series of spots on the edge 

of a cardboard chart and cover with cellophane tape. 

Label each spot with the figure of parts per million 

of copper to which it corresponds. Prepare new 

standards with each new batch of reagent paper. 

Procedure 

Preparation of sample solution. --Fuse 0. 1 g of 

soil with 0. 5 g (or a 0. 5 mllucite spoonful) of potassium bisulfate in a culture tube (18 by 150 mm) until 

a dull-red quiescent melt is obtained. As the tube 

cools, rotate it to allow the molten material to crystallize in a thin layer on the walls of the tube. .To 

the cooled tube add 3 ml of 13. 3 per-cent sodium 

citrate solution and boil until the melt disintegrates. 

Cool, add ammonium hydroxide until a piece of 

litmus paper in the solution turns blue, dilute to 5 ml 

with water; and add 1 ml of 50 percent acetic acid 

solution; Place a Stevens Extraction Stick in the test 

solution, insert a deflated rubber ear syrmge_into 

the top of the extraction stick and allow to stand lintil 

a sufficiently large aliquot has filtered. 

Determination of copper. --Make a confined spot 

test with 0. 2 ml of the sample solution in a chromograph containing rubean~ acid reagent paper in the 

manner described for the nickel determination. When 

the spots are dry9 compare with the chart of standard 

copper rubeanate spots. To preserve the spots for 

future reference, place the dry strip of reagent paper 

containing the test spots on a slightly longer piece of 

cellophane tape, with the spots faced downward against 

· the adhesive and mount the strip on a page in a notebook. 
Determination of Cobalt in Soils and Rocks 

The following directions for the determination of 

cobalt in soils and· rocks were given by Almond and Bloom 

(1951) . . The method as described is. suitable fo determine 

the cobalt content of soils containing from 10 to 400 ppm. 

Generally a· value repqrted by the fi~ld method is dependable to within:!:. 40 percenfof the value obtained by a laboratory procedure. The acidity of the sample solution must be 

carefully adjusted to prevent interference by iron and to 

assure complete precipitation of the cobalt compound. 

Cobalt is precipitated with 2-nitroso-1-naphtholreagent 

in the chromograph, and 8.fter filtration the confined spot 

thus obtained is compared with a standard series of 

confined spots . .. A large body of data can be collected 

within a short span of time since about 25 determinations can be completed per man day. The method has 

been successfully used in geochemical· prospecting. 

Reagents and appa,ratus 

2-Nitroso-1-naphthol, 0. 01 percent. Dissolve 

0. 01 g of 2-nitroso-1-naphthol in 100 ml of water to 

which 4 drops of 1 N NaOH solution have been added. 

Sodium hydrox_ide, 1 N. Dissolve 40 g NaOH 

in water and dilute to 1 liter. 

Potassium bisulfate, C. P. grade . .. Pulverize. 

Sodium citrate solution, 50 percent. Dissolve 

50 g Na3c6

H507" 5 1/2 H2o in water and dilute to 

100 ml. 

Litmus paper, red. 

Borate buffer solution, pH about 6: 5. Dis-solve 

19 gNa2B407.10H20 in 1 liter ofwater. Add 17 ml 

1 + 1 ·hydrochloric acid. 

Sulfuric acid 1 N. Add.28. 5 ml concentrated 

sulfuric acid to about 500 ml of water and dilute to 

1 liter. 

Cobalt standard solution, 0. 01 percent. Dissolve 

Q. 04 g CoCl2. 6H20 in water, add 1 ml of 1+ 1 hydrochloric acid and dilute to 100 ml. Prepare more dilute 

solutions from this stock solution. 

Water. Pass tap water through resin demineralizer. See "Apparatus." 

Gasoline stove. 

Fusion and digestion rack . . See "Special 

Apparatus. " 

.Stevens Extraction Sticks. See "Special 

Apparatus." · 

Culture tubes. - 16 by 150 mm, pyrex, calibrated 

at 10 ml. 

Balance. A torsion balance with a sensitivity 

of 2 mg is . satisfactory. 

Ear syringes, 6, rubber; adult size. 

Pipettes. 2 .. 0. 5 ml, serological 

2 - 2. ml, volumetr~c 

2 - 5. ml, volumetric 

19 

Filter paper. Whatman no. 50, cut in 7/16 in. 

strips~ 

Mullite mortar and pestle. Outside diameter 

. of mortar, 75 mm. 

Chromograph. See "Special Apparatus." 

Preparation of standard spots 

Prepare a series of spots representing 10 to 

400 ppm. of cobalt in the soil as follows: To a ~ies 

of 0. 1 g cobalt-free .soil samples, add O, 1, 3, 8, 

10, 20, and 40 micrograms of cobalt from the sta dard cobalt solution. · Evaporate to dryness over a 

steam bath. Add the flux, fuse and prepare standards 

spots by the procedure below. Mount the dry spots 

on the edge of. a cardboard with cellophane tape and 

label as-ppm iil the soil on the basis of a 0. 1 g sample. 

Procedure 

Mix 0. 1 g of finely ground soil or rock sample 

with 0. 4 g pulverized potassium bisulfate in a pyrex 

culture tube and fuse for 5 min. Cool, rotating the 

tube so that the melt solidifies in a thin layer on the 

sides of the tube. Add 5 ml of the sodium citrate 

solution and digest 'in a boiling water bath until the 

melt disintewates. Add a small piece of litmus 

paper and 1 N sodium hydroxide dropwise until the 

paper turns blue. Add 2 ml of borate buffer, ·then 

sufficient 1 N sulfuric acid to make the solution acid 

to litmus. Dilute to 10 ml with.metal-free water. 

Place a Stevens Extraction Stick in the culttire tube 

and apply suction to the upper end of stick with an 

ear syringe. Insert a strip of filter_ paper in reagentpaper slot of the chromograph, tighten the metal 

coupling to press the glass pipe filter head firmly 

against the filter paper, and adjust the water level to 

the base of the connector tube. Transfer 0. 2 ml of 

· the filtered sample solution to the filter head of the 

chromograph and.add 0. 1 ml of the 2-nitroso-1-naphthol reagent. Squeeze the rubber adjustor bulb and 

open the stopcock to connect the filter head with the 

bulb, and squeeze the bulb until the water column 

rises to the upper timing mark. Turn the stopcock 

into poSition so that drainage takes place through the 

slow capillary. After filtration is complete, add 

1 drop of 1 N sulfuric acid, to the colored spot and 

drain again. Remove the filter head, write the sample number adjacent to the spot on the paper, remove 

the strip of paper and allow the spot to dry •. ·. Compare 

the spot with the standards. Wash and dry the chromograph parts that come in contact with the filter 

paper to remove traces of the acid. With samples 

containing more than 400 ppm, dilute an aliquot of 

the sample solution and prepare_ another ~po.t • 

Determination of Molybdenum in Soils and Rocks 

A more _complete discussion of the method is 

given by Warel (1951a). The procedure given below 

can be used without modification to determine from 

1 to 32 ppm of molybdenum in soils and rocks. Data 

given in the original publication shows that duplicate 

determinations on soils containing less than 10 ppm 

of molybdenum-agree -within 1 ppm. A carbonate 

fusion and a subsequent aqueous leaching removes 

practically all the iron ·and other elements which 

form insoluble hydroxides. Tungsten interference 
is prevented by the addition of tartrate to the test 

solution. An isop:ropyl ether. extraction separates 

molybdenum from the remaining elements which interfere. The field method is essentially a "test tube" 

method for the determination of trace quantities of 

molybdenum in soils and rocks. The minute amount 

of molybdenum obtained from a 0. 025 g sample of 

soil or rock reacts under reducing conditions with 

thiocyanate to form an amber-colored complex ion 

which rarely is visible in the relatively large aqueous 

solution. The complex ion is, however, mo.re soluble 

in certain organic solvents than in the aqueous solution and can be extracted by and concentrated in a very 

small volume of isopropyl ether. If the extraction is 

carried out in an ordinary test tube, the ether separates 

as a shallow layer over the aqueous sample solu.., 

tion. As little as 0. 005 microgram of molybdenum 

per ml of aqueous solution can be determined. The 

simplicity of the method as well as the speed--30 or 

more molybdenum determinations per man day--makes 

this method a valuable tool in the hands of the modern 

prospector. 

Reagents and apparatus . 

Flux, a mixture-ot equal parts by weight of 

sodium carbonate-and potassium nitr_ate, ground to 

pass an 80~mesh silk bolting cloth sieve, thoroughly 

mixed, and passed through sieve again. 

. Sodium tartrate; reagent quality. 

Potassium thiocyanate, D percent. Dissolve 

10 g ·of KSCN in 200 ml of water. 

Stannous chloride, 10 percent. Dissolve 10 g of 

SnC 12~2H20 · in 100 ml of 2 N hydrochloric acid. Add 

tin to improve the stability. Prepare fresh solutions 

at weekly intervals. · 

Standard molybdenum solution. 0. 01 percent. 

Dissolve 0. 075 g of pure :Mo03:in l N NaOH, dilute 

with water, add 1 N hydrochlOric acid until solution 

is just acid, and dilute to 500 ml with water. This 

solution contains 100 micrograms of Mo per ml. 

Standard molybdenum solution, 0. 0001 percent. 

Prepare daily at least 1 hr befor~ use, by adding 1 ml 

of the 0. 01 percent solution to 50 ml of water and 

diluting to 100 ml. 

Hydrochloric acid, concentrated C. P. grade. 

· Potassium nitrate, 1 N. Dissolve 10 g of KN03 

in 100 ml of water •. 

Isopropyl ether. Practical or C P. grades are 

suitable provided peroxides are absent. Unless specially packaged, ·an dry ethers on standing· tend to 

form explosive peroxides. Peroxides of isopropyl 

ether inter.fere With the molybdenum method. To test 

for peroxides, shake 5 ml of e.ther with 5 ml of an 

acidified aqueous solution of potassium iodide. If 

the iodide solution shows more than a faint yellow 

color, due to free iodine produced by the peroxides, 

the ether con.tains appreciable quantities of peroxides 

and should not b~·, used. ·Shake peroxide-free ether 

with 1/10 its volume of equal amounts of stannous 

chloride and p6tassium thiocyanate solutions on the 

day during which it. is to be used. 

20 

Phenolphthalein indicator, l percent. Dissolve 

1 g of phenolphthalein i~ ~~0 ml of alcohol. . . 

Lucite spoon, ·a, luc'ite bar· with cavity of 0. 25 ml 

(7 mm diameter, 6. 5 mrp· deep) dril~ed near one end. 

.. Mullite mortar and pestle, ·outside diameter -of 

mortar, 75 mm. 

1 sieve, 80 mesh. See "Spedal Apparatus." 

1 camel's-hair brush, length of brush. part, 

18 mm. ' 

1 small spatula, length of blade, 50 mm. 

1 pyrex volumetric flask with stopper, 100 ml. 

· 20 pyrex culture tubes, 16 by. 150 mm, marked 

at '5 ml. · . : . ··~ · 

Pyrex culture tubes, 16 by 150 ~!!iz) -unmarked. 

One is required for each determination. · ·· . . 

3 serological pipettes, 1 ml, calibrated in 

tenths of a ml. · " · ., 

2 serological pipettes, 1 ml, calibrated in 

hlindredths of a ml. · , .. . · . · 

1 serological pipette, 10, II].~_( ~l~brated in 

tenths of a ml. · 

1 test tube rack, capacity at least 20 tubes. 

1 digestion and fusion rack. · See ''Special 

Apparatus." 

Balance, torsion, with sensitivity of 2 mg. 

Stevens Extraction Sticks. See "Special 

Apparatus." 

1 Gasoline stove. 

Water, metal-free. Pass tap water through 

resin demineralizer. See "Special Apparatus. " . · 

Cork stoppers, for the culture tubes. 

1 fusion rack. See "special Apparatus." 

Procedure 

Preparation of sample solution. --In the mullite 

mortar mix thoroughly 0. 1 g of the finely ground 

sample with 0. 5 g of the flux. Transfer the mixture 

to an unmarked culture tube and tap gently to dislodge 

the sample from the side of the tube.. Heat and .rotate 

the tube in the fusion rack ·over the gasoline stove to 

effect fusion. Usually, 4 to u min are required; by 

· . the time all the sample has been attacked, the tube 

is filled with brown fumes from the nitrate decomposition. After the fusion is complete,_ remove the 

tubes from the fusion raci{, place iri a test-tube rack 

and allow to cool. While the tubes are cooling, fill 

the top of the metal case of·-the gas~line. stove about 

hail full with water. Insert the digestion and fuSion 

rack in water bath. · Place on the stove .and bring the 

water to a boil. ·Pipette· 4 ml of metal-free water 
into each tube and place in the boiling water. After 

3 min insert a cor ked Stevens Extraction Stick into 

the culture tube and let the tube remain in the boiling 

water bath for 3 min or until air bubbles are escapfug 

freely from the lower end of the stick. Remove the 

culture tube from the water bath and place in a test 

tube rack to cool. As the system cools, a clear filtrate from the aqueous extraction of the fused mass 

is drawn into the extractor. Transfer a 1 ml aliquot 

of the filtrate representing 0. 025 g of soil, to a clean 

calibrated culture tube. Add 1 drop of indicator and 

1 N hydrochloric acid drop by drop, until the red 

color of the solution 'disappears. Avoid an excess. 

Dissolve one 0. 25 ml lucite spoonful (0.2 g) of sodium 

tartrate in the solution and add water to the 5 ml mark. 

Preparation of standards. --Pipette the appropriate volume of the 0. 0001 percent standard solution 

into culture tubes a.s follows: · 

Standard Volume of standard Molybdenum content 

required micrograms 

milliliter 

a 0.03 0.03 

b .og .0~ c .o .o 

d -15 .15. e .20 .20 

f -~0 -~0 g • 0 • 0 

h .so .so 

i .55 .55 

j .80 .80 

To each tube add n. 5 ml of l N potassium nitrate, 

and one 0. 25 ml lucite spoonful of sodium tartrate. 

Add about 2 ml of water and sha.ke to effect a clear 

solution. Dilute to 5 ml with water. 

Estimation. --To the sample solution and to each 

standard, add 0. 5 ml of concentrated hydrochloric acid 

and shake to liberate carbon dioxide. Add 0,3 ml ,of 

5 percent potassium thiocyanate and 0. 5 ml of stannous . 

chloride reagent with shaking after each addition. Allow 

the solution to stand for 1/2 to 1 min, add Q.3 ml of 

isopropyl ether and shake vigorously. Place a cork in 

each tube to prevent evaporation of the ether. View the 

amber -colored organic layer against a white background 

and compare with standard solutions. Multiply the number of micrograms ofmolybdenum found in the sample 

. aliquot by 40 to convert the results to ppm, 

Determination of Lead in Soils and Rocks 

The procedure for the determination of traces 

of lead in soils is based on the method us~d by Almond 

and Morris (1951). A nitric acid digestion has been 

found to dissolve lead more completely than the extraction used by Almond and Morris and is recomm.ended here. A 0.1 g sample is suitable for determination of lead in samples ranging from 10 to 1000 ppm. 

The lead estimation is made with dithizone in the 

21 

presence of cyanide as a complexing agent for other 

reacting metals. The oxidation product formed when 

an aqueous solution is shaken with dithizone in the 

presence of citrate, iron (III) and cyanide is a major 

source of error, but this is avoided in part by diluting 

the aliquot and by using freshly prepared dithizone. 

Duplicate samples can be determined to within 20 percent and generally th~ value reported differs from a 

careful laboratory determination by less than 50 percent. About 35 samples can be determined per man 

day. The method has been used in geochemical . prospecting. 

Reagents and Apparatus 

Potassium cyanide, 10 perce.nt. Dissolve 50 g 

KCN in 75 ml water and shake successively with 

small portions of 0. 01 percent dithizone solution until 

the final carbon tetrachloride layer is green. ~xtract 

the excess dithizone dissolved in the aqueous layer 

with successive portions of chloroformand discard 

the chloroform. The final extraction should be colorless. Dilute the solution to 500 ml with metal-free 

water. 

Pota;5sium cyanide, 0. 1 percent. Add 50 rhl metalfree water to 100 ml graduated cylinder, add about 

1 ml of the 10 percent potassium cyanide solution to 

cylinder and make the volume up to 100 ml with water. 

Ins·ert stopper and shake. Caution: Potassium cyanide is exceedingly poisonous; a very small amount 

taken internally is fatal. Therefore, never transfer 

a potassium cyanide solution with a pipette; always 

wash hands immediately after handling . the reagent 

and its solutions. 

Acidification of cyanide solutions produces a 

lethal gas (HCN). Never store near acids. Exercise 

meticulous care to avoid any possible contact of the 

salt or its solution with acids resulting from breakage in transport. Never acidify solutions containing 

cyanide. Always wash thoroughly vessels in which 

the reagent has been used. 

Ammonium citrate solution, 10 percent. Dissolve lOO g (NH4J2HCaH5o7 in about 400 ml metalfree water. Shake with successive portions 0. 01 percent dithizone solution until the carbon tetrachloride 

phase is green, Extract the excess dithizone dissolved in the aqueous phase by shaking with successive portions of chloroform and discard the chloroform. The final extract should be colorless. Dilute 

the aqueous phase to lliter. 

Ammonium hydroxide, 1 :N. Dilute 70 ml concentrated ammonia with water to 1 liter. 

Dithizone (diphenylthiocarbazone), 0, 01 percent 

weight per volume. Dissolve 0, 01 g dithizone in 

100 ml carbon tetrachloride. 
Dithizone, 0. 001 percent. Dilute 10 ml of the 

0. 01 percent dithizone with carbon tetrachloride to 

100 ml. Prepare daily and keep in a pyrex bottle covered with a dark-colored paper. 

Standard lead solution, 0. 01 percent. Dissolve 

0. 016 g dry lead nitrate in 100 ml of solution containing 1 drop of concentrated nitric acid. This solution 

contains 100 micrograms lead per ml. 

Standard lead solution, 0. 001 percent. Add 

10 ml 0. 01 percent to about 50 ml 1 N nitric acid and 

make up to 100 ml with 1 N nitric acid. This solution contains 10 micrograms lead per ml. 

Nitric acid, concentrated. 

Nitric acid, 1+3, add 1 volume concentrated acid 

to 3 volumes water. 

Water. Pass tap water through a resin de mineralizer. See "Special Apparatus." 

Thymol blue indicator, 0. 04 percent. Dissolve 

0. 04 g of the sodium salt in 100 ml water. 

Digestion and fusion rack. See "Special 

Apparatus." 

Mullite mortar and pestle, diameter of mortar, 

75 mm. 

Balance, torison, sensitivity, 2 mg. 

1 gasoline stove. 

Sieve, 80 mesh. See "Special Apparatus." 

1 serological pipette, 0.1 ml, graduated in 

hundredths of a ml. 

1 serological pipette, ·1 ml, graduated in tenths 

of a ml. 

1 serological pipette, 5 ml, graduated in tenths 

of a ml. 

2 volumetric pipettes, 5 ml. 

1 volumetric pipette, 10 ml. 

30 prJex culture tubes, 18 by 150 mm, marked 

at 2 and 1 ml. 

6 graduated cylinders, glass-stoppered, 100 ml. 

3 separatory funnels, Squibb type, 125 ml. 

30 Stevens Extraction Sticks. See '!Special 

Apparatus. " 

Procedure 

Extraction. --Place 0.1 g of the finely ground 

sample in a pyrex test tube, Prepare eight samples 

at a time. Add 2 ml of 1+3 nitric acid. Allow time 

for effervescence from carbonates to cease. · Place 

a Stevens Extraction Stick in the test tube and 'boil 

gently for 30 min. .· Cool. The solution filters into 

the extractor durinq cooling. 

22 

Estimation of lead. --Transfer the filtered solution to a clean culture tube and dilute with water to · 

10 ml mark. Shake and transfer a 5 ml aliquot to a 

125 ml pyrex separatory funnel. Add 5 ml of 10 percent ammonium citrate, 2 drops of thymol blue indicator and sufficient 1 N ammonium hydroxide to turn 

the solution distinctly yellow. Add 10 percent potassium cyanide until the entire solution just turns blue 

(pH about 8. 5). Add 5 ml of 0. 001 percent freshly 

prepared dithizone solution and shake gently for 5 sec. 

Drain the car. bon tetrachloride (lower) phase into a 

100 ml glass-stoppered pyrex graduated cylinder containing 10 ml of 0. 1 percent potassium cyanide solution. 

Shake the mixture for 3 sec. The unreacted dithizone 

is now in the aqueous phase while the pink lead dithizonate is in the carbon tetrachloride phase. From 

standards similarly prepared, estimate the amount of 

lead present. 

One microgram of lead gives a weak but perceptible pink, corresponding to 20 ppm lead in the original sample, and more than 3 micrograms is . diffic:lllt 

to estimate visually. If the first aliquot does not give 

a color in the suitable range, repeat using larger or 

smaller aliquots until a readable color is obtained. 

Determination of Silver in Soils and Rocks 

The procedure given below for the determination 

of traces of silver in soils and rocks is described in 

detail by Almond, Stevens and Lakin (1951). With a 

0. 5 g sample from 0. 2 to 20 ppm of silver can be 

estimated. The noble metals, as well as mercury 

and copper (I) also react with the reagent, but the 

method minimizes these interferences. Mercury is 

elimina~ed with organic matter by igniting the sample. 

Nitric acid, the digesting agent, oxidizes copper to 

copper (II), and has poor solvent action on gold. 

Silver is separated from the colored ions in 

nitric acid solution by collecting the silver salt of 

p-dimethylaminobenzai.rnodanine at the interface of an 

amyl alcohol aqueous extract, and then discarding the 

aqueous extract. This silver precipitate, in a dis- · 

persed state is filtered through the chromograph to 

form a. confined spot. The intensity of the confined 

spot remaining on the filter paper is a measure of the 

silver content of the original soil. About 20 samples 

can be analyzed per man day. Generally duplicate 

samples can be determined within 40 percent. The 

method is suitable for geochemical prospecting. 

Reagents and Apparatus 

Ammonium citrate, 25 percent. Dissolve 25 g 

ammonium citrate, {NR4)2HCeH507, in metal-free 

water and dilute to 100 ml. Shake with amyl alcohot 

in a 250 ml separatory funnel and allow to stand 4 hr. 

Drain the citrate from the solids in the interface and 

discard the amyl alcohol and solids. Repeat the process until no solids appear in the interface. 

Water. ·Pass tap water through resin demineralizer. See "special Apparatus." · 

Nitric acid, concentrated. C. P. gtade. 

Ammonium hydroxide, concentrated, C. P. grade. 

Acetic acid, glacial, C. P. grade. 
p-Dimethylaminobenzalrhodanine,. 0.05 percent. 

Dissolve 0. 05 g in 100 ml of glacial acetic acid. 

Amyl alcohol, B. P. 136-138 C. 

Ethyl alcohol, 95 percent, U. S. P. 

Standard silver solution A,- 0. 01 perceht. Dissolve o. o16 g of silver nitrate, dried at 110 c, in 

100 ml of 1 N ammonium hydroxide. 

Standard silver solution B, 0.001 percent. 

Transfer 10 ml solution A to a 100 ml volumetric flask 

containing about 50 ml 1 N ammonium hydroxide and 

dilute to volume with 1 N ammonium hydroxide. 

Shake thoroughly. 

Standard silver solution C, 0. 0001 percent. 

Transfer 10 ml solution B to a 100 ml volumetric flask 

containing about 50 ml 1 N ammonium hydroxide and 

dilute to volume with 1 N ammonium hydroxide. Shake 

thoroughly. · 

100 Stevens Extraction Sticks. See "Special 

Apparatus. " 

20 separatory funnels. 60 ml, Squibb. 

6 glass chromographs. See "Special Apparatus. " 

100 pyrex culture tubes, 16 by 150 mm. 

1 gasoline stove. 

Electric hot plate, llOV a-c, variable temperature control, 6 by 6 in. heating surface. 

Munktell Swedish filter paper, no. OA. Cut in 

strips 7/16-in. wide .. 

Balance, a torsion balance, sensitivity 2 mg. 

Sample Add Standard B 

milliliter 

a 

b 

c 

d 

e .1 

f .3 

g .6 

h 1.2 

Mount the series of spots on the edge of a cardboard chart and cover with cellophane tape. Label 

each spot with the value in parts per million of silver 

to which it corresponds. 

Procedure 

Preparation of sample solution. --Place a 0. 5 g 

soil or rock sample, ground to pass an 80-mesh sieve, 

in a no. 0 porcelain crucible. Heat for 10 min at 

about 800 C (dull red heat). Cool and add 10 ml concentrated nitric acid. Place on a hot plate covered 

with a sheet of asbestos paper. Set at very low heat 

(40 C to 50 C.) so that about 1 1/2 ml of acid remains 

after 12 hr of digestion. Allow the sample to · digest 

on the hot plate overnight. Transfer the sample and 

23 

40 porcelain crucibles, no. 0. , high form. 

Litmu,s paper, blue. 

1 serological pipette, 1 ml, graduated in tenths 

of a ml. 

1 serological pipette, 10 ml, graduated in tenths 

of a ml. 

3 graduated cylinders, 5 ml, pyrex. 

1 graduated cylinder, 10 ml, pyrex. 

Digestion and fusion rack. See "Special 

Apparatus. " 

Mullite mortar and pestle, outside diameter of 

mortar, 75 mm. 

Sieve, 80 mesh. See "Special Apparatus." 

1 wash bottle, 250 ml, polyethylene. 

1 pyrex glass rod, 150 mm in length. 

Preparation of standard spots 

Prepare a series of spots representing values 

ranging from 0 to 24 ppm as follows: Label eight 

no. 0 crucibles, a to h, inclusive, and to each add 

0. 5 g finely ground silver -free soil and roast 10 min. 

Cool. To each crucible add standard solution B or C, 

in the quantities indicated below. Evaporate to dry:-

ness. Add 10 ml concentrated nitric acid to each 

crucible and prepare standard · spots as direCted 

in the procedure given below. Spot "b" represents 0. 2 ppm silver in a sample, since 0.1 microgram of silver has been added to a 0. 5 g sample. 

Add Standard C Micrograms 

milliliter silver added 

o.o 

0.1 .1 

.3 

.6 ·3 .6 

1.0 

3.0 

6.0 

12.0 

nitric acid to a 16 by 150 mm culture tube, and wash 

the soil remaining in the crucible into the tube with 

concentrated nitric acid using a volume of about 

1/2 ml. Rinse the crucible again with 1/2 ml of water 

and add to the contents of the culture tube. ·Insert a 

firmly stoppered Steve:qs Extraction Stick into the 

test tube and place in a digestion and fusion rack. 

Place the rack on the gasoline stove and digest for 

10 min. Remove the culture tube from the heat. When 

cool, the solution is in the extractor. 

Separation and estimation of silver. --Transfer 

the filtered solution from the Extraction Stick to a 

60 ml separatory funnel containing 10 ml metal-free 

water. Rinse the extractor with 10 ml water and combine the washings with the original extract in the 
separatory funnel. Add 3 ml of 25 percent ammonium 

citrate solution, shake to mix, and make the solution 

alkaline to litmus by adding ammonium hydroxide 

dropwise. Test frequently by alternately dipping a 

glass rod into .the solution and touching it to a fresh 

piece of litmus paper. Add 5 ml of glacial acetic acid 

and 0. 1 ml of 0. 05 percent" p-dimethylaminobenzalrhodanine, and mix thoroughly. Allow to cool. -Add 

3 ml amyl alcohol, shake for 30 sec and allow to stand 

for 30 min to permit the phases to separate. Drain 

until about 1/2 ml of the aqueous (lower) phase remains, 

add about 1 ml of water and drain again until about 1/2 

ml of aqueous phase remains. Add 1 ml ethyl· alcohol and 

shake to disperse the precipitate. Place a strip of filter 

paper in the slot in the head of the chromograph and tighten 

the coupling to seal the filter paper between the two sections of pipe. Adjust the water column to the upper timing 

mark and transfer the contents of the separatory funnel to 

the head of the chromograph. Open the fast capillary of 

the chromograph and turn the stopcock so that the drainage 

is through the capill~ry. When filtration is complete, remove the paper from the chromograph, write the number 

of sample adjacent to the spot and ·mount the dry spots in 

the analyst's notebookwithcellophane tape. Comparethe 

dried spot on the filter paper with a standard series of 

spots. After the analysis is cQmplete, wash the separatory 

funnel with nitric acid, rinse four times with tap water and 

finally with metal-free water to remove traces of ethyl alcohol. Carefully clean the glass filter head of the 

chromograph similarly. 

Determination of Tungsten in Soils 

A more complete discussion of the method is 

given by Ward j(l951b). The procedure given below 

can be used without modification on soils containing 

20 to 400 ppm of tungsten; however, if the size of the 

aliquot taken for the estimation is varied, the method 

can be used on soils containing 10 to 800 ppm of tungsten. The results obtained by the field method on 12 

out of 14 representative soil samples are within ± 40 

percent of those obtained by a laboratory method., An 

aqueous extraction of the carbonate fusiori separates 

tungsten from iron, titanium, and other elements 

which form insoluble hydroxides. Later, an isopropyl 

ether extraction of the acidified sample solution under 

reducing conditions and in the presence of an alkali 

thiocyanate serves to separate tungsten from small 

amounts of tantalum, uranium, phosphorus, boron, 

and from as much as 1, 000 micrograms of vanadium. 

Although copper reacts with thiocyanate to form the 

insoluble cuprous thiocyanate, the reaction causes no 

interference in the field method. Although large 

amounts of molybdenum interfere with the field method, 

a higher acid concentration bleaches the color of the 

molybdenum thiocyanate and prevents that interference. 

This field method is essentially a "test tube" method 

which requires a minimum amount of reagents and 

simple equipment. With a little practice the average 

individual can determine the tungsten content of as 

many as 30 soil samples per day in temporary quarters and under a wide range of conditions. The field 

method should prove useful in geochemical prospecting programs. · 

Reagents and Apparatus 

Flux, a mixt~e .by! weight of 5 parts sodium 

carbonate, 4 parts sodium chloride, and 1 part potassium nitrate, ground to pass an 80-mesh silk 

24 

bolting cloth sieve, thoroughly mixed, and passed 

through the sieve again. 

Potassium thiocf!Pate, 25 percent. Dissolve 

25 g KSCN in water and dilute 100 ml. 

Hydrochloric acid, ' concentrated, G.P. grade 

Stannous chloride. Dissolve 10 g SnCl2.2H20 

in concentrated hydrochloric acid and dilute to 100 ml 

with the acid. 

Standard tungsten solution, 0. 01 percent. Solution A. .Dissolve 0. 69 g Na2W04.2H20 in water and 

dilute to 500 ml. The solution contains 100 micrograms 

of tungsten per ml. 

Standard tungsten solution, 0.0005 percent. Solution B. Because the concentration decreases on 

standing~one should prepare it daily by diluting 5 ml 

of solution A with water to 100 ml and mixing thoroughly. 

Isopropyl ether. Practical or C. P. grades are 

suitable provided peroxides are absent. Unless spec-. 

ially packaged, all dry ethers on standing tend to form 

explosive peroxides. Peroxides of isopropyl ether 

interfere with the tungsten method. To test for peroxides· shake 5 ml of ether with 5 ml of an acidified 

aqueous SQlution of potassium iodide. If the iodide 

solution shows more than a faint yellow color~ due to 

free iodine produced by the peroxides, the ether contains appreciable quantities of peroxides and should 

not be used. Shake peroxide-free ether with 1/10 its 

· volume of equal amounts of stannous chloride and 

potassium thiocyanate solutions on the day during 

:which it is to be used. 

Water. Pass tap water through resin de mineralizer. See "Special Apparatus. " 

Mullite mortar and pestle, outside diameter of 

mortar, 75 mm. 

1 sieve, 80-mesh. See "Special Apparatus!' 

1 camel's-hair brush, length of brush part, 

18 mm. 

1 pyrex volumetric flask with stopper. 100 ml. 

20 pyrex culture tubes (16 by 150 mm), marked 

at 5 ml. 

Pyrex culture tubes (16 by 150 mm); unmarked. 

One is required for each determination. 

1 serological pipette, 1 ml, calibrated in· hundredths of a ml. 

1 serological pipette, 2 ml, calibrated in tenths 

of a ml. 

2 serological pipettes, 5 ml, calibrated in tenths 

of a ml. 

1 test tube rack, capacity 20 tubes. 

Balance, torsion, s~nsitivity 2 mg. 
Stevens Extraction Sticks. See "Special 

Apparatus. " 

l portable gasoline stove. 

1 fusion rack. See "Special Apparatus." 

l water bath. The top of the gasoline stove 

container filled with water to about 2/3 of its capacity 

is an excellent water bath. 

1 digestion and fusion rack. A round rack fitting inside the top of the gasoline stove container and 

holding 16 tubes was used. See "Special Apparatus." 

Cork stoppers no. 5 for the culture tubes. 

l thermometer, 0 to llO C. 

Procedure 

Preparation of sample solution. Weigh out 

0.25 g of the finely ground soil and transfer to a culture tube. Tap the tube gently to dislodge sample 

from the sides and add 1.25 g of flux. Mix the sample 

and flux by alternately rotating and tapping the tubes. 

Place the tube in the fusion rack over the gasoline 

stove and allow the contents to fuse 5 to 6 min. Rotate the tube occasionally to insure a thorough attack 

of the sample. After the fusion is complete, remove 

the tube from the rack and allow to cool. Pipette 

5 ml of metal-free water into the tube, and place the 

tube in a boiling water bath. After 3 min insert a 

corked Stevens Extraction Stick into the culture tube 

and iet the tube remain in the boiling water bath for 

3 min or until air bubbles are escaping freely from 

the lower end of the extraction stick. Remove the 

culture tube from the water bath and place in a testtube rack to cool. As the system cools, a clear filtrate from the aqueous extraction of the fused mass is 

is drawn into the extractor. Transfer a l ml aliquot 

of the filtrate, representing 0,05 g of soil, to a clean 

culture tube and add water to make the volume up to 

the 5 ml mark. 

Preparation of standards. --Prepare a series of 

standard solutions bJ pipetting the required volumes 

of standard solution B into separate culture tubes and 

adding water to the 5 ml mark. 

Standard Volume of solution B 

required 

milliliter 

a ---------------

b ---------------

c ---------------

d ---------------

e ---------------

f ---------------

g ----~---------­

h ---------------

0.2 

.4 

.6 

.8 

1.0 

2.0 

3.0 

4.0 

Tt.ingsten 

content 

micrograms 

1 

2 

3 

4 

5 

10 

15 

20 

Estimation. --Add 4 ml of stannous chloride and 

0. 5 ml of potassium thiocyanate reagents to the sample solution and to each· standard solution. Place the 

tubes in a water-bath maintained at a temperature of 

90 C to 95 C for 5 min or until one observes a moderate evolution of hydrogen sulfide. If the altitude 

causes the water to boil below the specified temper25 

ature, allow the tubes to remain in the water bath 

until hydrogen sulfide evolves freely. Remove the 

tubes from the water bath, cool, add 0. 5 ml of potassium thiocyanate reagent and 0.3 ml of isopropyl ether. 

Insert a clean cork into the tube and shake 5 sec to 

extract the tungsten thiocyanate complex ion into the 

ether. Compare the intensity of the yellowish-green 

color of the ether layer over the sample solution with 

that obtained over the standard solution. If the color 

oi the ether layer over the sample is amber instead 

of yellowish-green, add about 5 ml of concentrated 

hydrochloric acid and shake to bleach the amber color. 

Since a small amount of the isopropyl ether dissolves 

in the aqueous phase during this process, add an additional 0.1 ml of isopropyl ether in order to make 

valid comparisons. 

Multiply the number of micrograms of tungsten 

found in the aliquot by 20 to convert the results to 

parts per million. The procedure is suitable for soils 

containing from 20 to 400 ppm of tungsten; but, i1 one 

adjusts the aliquot, he can decrease the lower limit 

to 10 ppm. The upper limit is determined by the accuracy with which the operator can measure small 

aliquots. VJith materials containing rriore than 0.1 

percent of tungsten, the field method ·of North and 

Grimaldi '(1946) is convenient. 

After · the analysis is complete, wash and retain 

the calibrated culture tube and extraction stick for 

future use. Discard the tube used for the fusion as 

the action of the flux makes further · use impracticable. 

Determination of Readily Soluble Copper, 

Zinc, and Lead in-Soils and Rocks: 

Sulfuric Acid Extraction 

The procedure for the determination of traces of 

copper, zinc, and lead is described by Almond and 

Morris (1951). A dilute sulfuric acid solution is used 

to dissolve trace amounts of copper, zinc, and lead 

from the sample, and dithizone is the reagent used to 

estimate the three metals separately. The sulfuric 

acid extraction is used because it is a simple procedure and indications of the content of the three 

metals in a sample can be obtained from the same 

sample solution. About 20 samples can be analyzed 

daily for copper, zinc, and lead. The method is a 

useful tool for survey work in geochemical prospecting. 

Reagents and Apparatus 

Potassium cyanide, 10 percent. Dissolve 

50 g KCN in 75 ml of water and shake with successive 

small portions of 0.01 percent dithizone solution until 

the final carbon tetrachloride layer is green. Extract 

the excess dithizone in the aqueous layer with successive 

portions of chloroform, and discard the chloroform. 

The final extract should be colorless. Dilute to 500 ml. 

Potassium cyanide, 0.1 percent. Add 50 ml 

metal•free water to ldo ml graduated cylinder, add 

about 1 ml 10 percent solution to cylinder and make 

volume up to 100 ml with water. Stopper and shake. 

Caution: Potassium cyanide is exceedingly poisonous; 

a very small amount taken internally is fatal. Therefore, never transfer a potassium cyanide solution 

with a pipette; always wash the hands immediately 

after handling the reagent and its solutions. 
Acidification of cyanide solutions produces a 

lethal gas (HCN). Never store near acids. Use 

meticulous care to avoid any possible contact of 

the salt or its· solution with acids resulting from 

breakage in transport. Never acidify solutions containing cyanide. Always thoroughly wash vessels 

in which the reagent has been used. 

Ammonium hydroxide, 1 N. Dilute 70 ml 

concentrated ammonia to one liter. 

Sodium thiosulfate, 50 g Na2S203. 5H20 in 100 

ml water. Remove reacting heavy metals by shaking 

with 0. 01 percent dithizone solution. 

Sulfuric acid, 1 N. Add 28. 5 ml concentrated 

sulfuric acid to about 500 ml water and dilute to 

1000 ml. 

Ammonium citrate solution, 10 percent. 

Dissolve 100 g (NH4)2HC6H507 in about 400 ml of 

metal-free water. Shake with successive portions 

of 0. 01 percent dithizone solution until tb~ carbon 

tetrachloride phase is green. Extract the excess 

dithizone dissolved in the aqueous phase by shaking 

with successive portions of chloroform and discard 

the chloroform. The final extract should be colorless. Dilute the aqueous phase to 1 liter. 

Dithizone (diphenylthiocarbazone), 0. 01 percent 

weight per volume. Dissolve 0. 01 g dithizone in 100 

ml carbon tetrachloride. 

Dithizone, 0. 001 percent. Dilute 10 ml 0. 01 

percent dithizone with carbon tetrachloride to 100 

ml. Prepare daily and keep in a pyrex bottle covered 

with a dark-colored paper. 

Sodium acetate, 2 N. Dissolve 164 g CH3COONa · 

· in metal-free water and dilute to 1 liter. 

Acetic acid, 2 N. Dilute 114 ml glacial acetic 

acid to 1liter with metal-free water. 

Acetate buffer, pH about 4. 75. Mix equal 

volumes 2 N sodium acetate and 2 N acetic acid and 

remove traces of zinc by shaking with 0. 01 percent 

dithizone solution. 

Thymol bl'ue indicator, 0. 04 percent. Dissolve 

0. 04 g of the sodium salt in 100 ml. of metal-free 

water. 

Water. Pass tap water through resin demineralizer. See "Special Apparatus." 

Standard copper solution, 0. 01 percent. Dissolve 0, 2 g of clear uneffloresced crystals of 

CuS04. 5H20 in water, add enough sulfuric acid to 

make the final acidity about 0. 1 Nand dilute to 500 

ml. One ml of this solution contains 100 micrograms. 

Standard zinc solution, 0. 01 percent in about 

0. 1 N hydrochloric acid. Dissolve 0. 1 g of reagentgrade 30-mesh zinc in concentrated hydrochloric 

acid and dilute to 1 liter. One ml of this solution 

contains 100 micrograms. 

Standard lead solution, 0, 1 percent. Dissolve 

0. 16 g of dry lead nitrate in 100 ml of solution 

26 

acidified with nitric acid. One ml of this solution 

contains 1, 000 micrograms. 

Fusion and digestion rack. See "Special Apparatus." 

Balance. Sensitivity, 2 mg. 

1 gasoline stove. 

Sieve, 80:-mesh. See "Special Apparatus." 

3 serological pipettes, 1. 0 ml, graduated in 

hundredths of a ml. 

1 serological pipette, 5.·0 ml, graduated in 

tenths of a ml. 

30 pyrex culture tubes, 25 by 200 mrri, marked 

at 30 and 40 ml. 

6 graduated cylinders, 100 ml, glass-stoppered 

pyrex. 

3 graduated cylinders, 5 ml, pyrex. 

3 separatory funnels, 125 ml, Squibb type, glassstoppered, pyrex. 

Procedure 

Extraction. --Place 1 g of the finely ground 

sample in a culture tube. Prepare eight samples at 

the same time. Add 30 ml of 1 N. sulfuric acid and 

reflux for 30 min. Dilute to 40 ml; reflux for an additional 5 min, and allow to cool. Take aliquots directly from the supernatant liquid. 

Estimation of copper. -~Transfer a 2 ml aliquot 

of the sulfuric acid solution to a 100 ml glass stoppered pyrex graduated cylinder, containing about 10 ml 

of water. Add 2 to 3 drops of thymol blue indicator, 

1 ml ammonium citrate, then l .N. ammonium hydroxide until the solution begins to turn yellow. The 

color should have a pink tinge. If it does not, back 

titrate with 1 N sulfuric acid until the pink begins to 

reappear. Add 5 ml of fresh 0. 001 percent solution 

of dithizone and shake for two minutes. Compare the 

mixed color with those of standard copper solutions. 

Four micrograms of copper produce a gray; 5 micrograms, a blue; and six micrograms, a purple color 

in the organic phaser Less than 4 micrograms of 

copper gives an indecisive color change, whereas 

more than 6 micrograms produces a color ranging 

from purple to pink, which is difficult to compare. _ 

If the first aliquot does not give a color in the suitable 

range, repeat using larger or smaller aliquots until 

a readable color is obtained. 

Estimation of zinc. --Transfer 1 rni of the 

sulfuric acid extract to a 100 ml graduated cylinder 

containing about 10 ml of water. Add 0. 5 ml of 

ammonium citrate, 2 to 3 drops of thymol blue, and 

ammonium hydroxide until the indicator turns yellow. 

Add 1 m1 of the sodium acetate buffer and 1 ml of 

sodium thiosulfate solution. Add 5 ml of 0, 001 percent fresh solution of dithizone and shake for 1 min. 

Estimate the zinc in the carbon tetrachloride phase 

by the mixed color .method. Zinc produces the 

following colors: 0. 5 microqrams, blue green; 
1 microgram, blue; 2 micrograms, purple; 3 

micrograms, violet; 4 micrograms, or more, 

purplish red. Use a smaller aliquot if a purplishred color results, or a larger aliquot if the green 

remains apparently unchanged. 

Estimation of-lead. --Trarts!er 2 ml of the 

sulfuric acid extract to a 125 ml separatory funnel, 

containing about 10 ml of water. Add 5 ml ammonium 

citrate, 2 drops of indicator, and sufficient ammonium 

hydroxide to turn the solution distinctly yellow. Add 

10 percent potassium cyanide until the entire solution 

just turns blue (pH about 8. 5). Add 5 ml of 0. 001 

percent freshly prepared dithizone solution and shake 

gently for 5 sec. Drain the carbon tetrachloride 

phase into a 100 ml graduated cylinder containing 

10 ml of 0. 1 percent putassium cyanide solution. 

Shake the mixture for 3 sec. Excess dithizone is 

now in the ;lqueous phase and the pink lead dithizonate is in the carbon tetrachloride phase. From 

standards similarly prepared, estimate the amount 

of lead present. 

One microgram of lead gives a weak but 

definite pink; more than 3 micrograms is difficult 

to estimate visually. If the iirst aliquot does not 

give a color in the suitable range, repeat using 

larger or smaller aliquots until the readable color 

is obtained. 

Determination of zinc in plants 

This method for the field determination of 

zinc in fresh plant leaves is described in detail 

by Reichen and Lakin {1949). The fresh leaves are 

collected with a leaf punch cutting discs of 1 sq em. 

Twenty of the discs are used as a sample. Results 

are calculated in micrograms per 100 discs. As an 

approximation for eastern vegetation 2 times micrograms per hundred discs gives parts per million on 

the dry weight basis. The.. method is suitable for 

determining from 50 to 2500 micrograms per 100 

discs or roughly 100 to 5000 ppm on air dry basis. 

Some zinc is lost during the ashing of the leaves, 

but the loss is not sufficient to impair the use of 

direct ashing for geochemical prospecting. The 

zinc losses during .ashing are generally less with 

fresh green vegetation than with air dried vegetation. 

Apparatus and chemicals are readily available and 

easily portable. Under favorable conditions, 40 or 

more determinations can be made per man day. The 

method may prove useful in geochemical prospecting. 

Reagents and apparatus 

Water. Pass tap water through resin demineralizer. See "Special Apparatus. " 

Acetate buffer. Dissolve 248 g sodium acetate 

(NaC2H302. 3H20)ih 900 ml of water. Add 11 ml 

glacial acetic acid and make up to 1 liter. Remove 

traces of zinc by shaking with successive portions of 

0. 01 percent dithizone solution until the green color 

of dithizone persists. 

Sodium thiosulfate, 50 g Na2S203. 5H20 in 100 

ml water. Remove reacting .heavy metals by shaking 

with 0, 01 percent dithizone solution. 

27 

Standard zinc solution, 0. 01 percent in about 

0. 1 N hydrochloric acid. Dissolve 0. 01 g reagentgrade 30 mesh zinc in concentrated hydrochloric 

acid and dilute to 100 ml with water. 

Standard_ zinc solution, 0. 0005 percent. Add 

2. 5 ml 0. 01 percent standard zinc solution to 35 ml 

acetate buffer and 5 ml sodium thiosulfate. Dilute 

to 50 ml with l N hydrochloric acid. This solution 

should be made fresh daily. One ml contains 5 micrograms of zinc. 

Hydrochloric acid, · lN. Dilute 83. 5 ml of concentrated hydrochloric acid to l liter with metal-free 

water. 

Dithizone solution, 0, 01 percent weight per 

volume. Dissolve 0. 01 g in 100 ml reagent-grade 

carbon tetrachloride. Store in cool, dark place. 

Dithizone solution, 0. 0025 percent weight per 

volume. Dilute 25 ml 0. 01 percent solution to 100 

ml with reagent-grade carbon tetrachloride. 

20 pyrex culture tubes, 18 by 150 mm, marked 

at 3, 10, and 11 ml. 

20 pyrex culture tubes, 16 by 150 mm, marked 

at 5 ml. 

1 test tube rack 

1 serological pipette, 5 ml, fitted with stopcock 

at upper end. 

1 graduated cylinder, 100 ml, or other suitable 

device in which to support pipette. 

1 serological pipette, 10 ml, graduated in tenths 

of a ml. 

1 camel's-hair brush. 

10 nickel crucibles about 40 mm in diameter a:pd 

30 mm high. 

1 leaf punch, similar to item no. 2-846 listed by 

Fisher Scientific Co. The punch cuts a disk 1 sq em 

in area. 

1 gasoline stove. 

Cork to fit both sizes of culture tubes. 

Procedure 

Place 20 disks (20 sq em, ctit from the leaves 

of the plant with the leaf punch) in a nickel dish and 

ash over the flame of the gasoline stove, heating only 

long· enough to burn the sample completely. · Transfer 

the ash to a test tube (1g by 150 mm) and rinse the 

dish with a little l N hydrochloric acid. Dilute to 3 

ml with 1 N hydrochloric acid, add 7 ml acetate buffer 

and 1 ml sodium thiosulfate, stopper with a clean 

cork, and mix by shaking. 

Preparation of standard. --Transfer 5 ml of the 

o. 0025 percent dithizone solution to a culture tube 
(16 by 150 mm). Add 1 ml 0. 0005 percent zinc 

standard and shake fo.r 1 min. Prepare fresh standards every 30 min because the color fades rapidly. 

. Estimation. --This step is essentially a tit-. 

ration. Place 5 ml of the 0. 0025 percent dithizone 

solution in a culture tube (16 by 150 mm), and add 

the sa.mple solution in increments of 1 ml, shaking 

vigoro~sly for 1 min after each addition. Continue 

the titration until the color of the carbon tetrachloride layer matches as nearly as possible that of 

the standard. If less than 1 ml of sample solution 

is needed to match the standard, repeat the titration on a tenfold dilution of the satnple solution. 

The zinc content of the sample corresponding 

to the volume of sample solution required in the 

titration to match the standard is found in table 5. 

Table 5.--Zinc content of plants corresponding to various volumes of sample solution 

VolUme required for Zinc. content 

closest matching of 

standard milliliter Micrograms per 100 sq em fresh material Approximate micrograms ~r gram air-dry weight (parts per million) 

Original sample solution: 

3 ~ ====================== 

2 

1 

Diluted sample solution: 

6 ----------------------

~ 

.. 

~g 

Bo 

125 

250 

400 

500 

600 

3 Boo 

2 

1 1,250 

2,500 

Since "Micrqgrams per area" i~ a comparatively unfamiliar manner of expressing trace element content of plant material, the calculations are 

given both in micrograms per gram (parts per million) and in micrograms per 100 sq em. ,No accurate . 

conversion from area to weight basis can be made. 

because of the variatic.n in the leaf struct1.u-e of different kinds of plants; however, for a group .of plants 

collected in the eastern United States, it has been 

found that multiplying the micrograms per 100 sq em 

by 2 will give the approximate micrograms per gram 

of air dried plant material. · 

Determination of nickel in plants 

A mote complete discussion of the method is 

given by Reichen (1951). Data given in the original 

publication show that the results obtained by the 

field method are generally within 30 percent of those 

obtained· by a conventional laboratory procedure. 

As little as 0, 025 percent nickel in plant ash can be 

determined and with a simple modification 0, 00~ 

percent nickel in plant ash can be detected. The ash 

obtained from fresh plant material is dissolved in 

dilute hydrochloric acid, and ammonia is added until 

the pH is 8. 8 as indicated by the color of thymol blue. 

A molybqate solution is added to complex silica 

and prevents the formation of a gel in the sample 

solution. The sampl~ solution is allowed to stand 

for about 15 min to permit calcium citrate to settle, 

otherwise it collects on the reagent paper· and obscures the color of the nickel spots. Large amounts of 

copper and cobalt interfere by consuming the reagent 

and in the presence of ferric iron cobalt may form . 

28 

100 

120 

160 

250 

500 

Boo 

1,000 

1,200 

1,600 

2,500 

5,000 

a red-brown precipitate with dimethylglyoxim~. As a large· excess of citrate !s present in the test solution, the latter kind of interference is unlikely. The 

use of fresh plant material and the collection of the 

red nickel dimethylglyoxime in a confined spot by 

means of the chromograph are unique features which 

contribute to the speed and simplicity of the field 

method, Since as many as 30 determinations can be 

made per man day in temporary quarters, the method 

should be· useful to the prospector in reconnaissance 

programs and in detailed surveys. 

Reagents and apparatus 

Hydrochloric acid, 1 + 1. 

Sodium citrate, 50 percent. Dissolve 50 g 

Na3C6H507. 5 1/2 H20 in 100 ml of water. 

Ammonium hydroxide, concentrated. 

Ammonium hydroxide, 1+ 1, freshly prepared. 

Thymol blue indicator., 0. 1 percent, Dissolve 

0. 1 g of the sodium salt in 100 ml of water. 

Molybdate solution. Dissolve 1 g Mo03 in a 

few ml dilute sodium hydroxide and dilute with water 

to 100 ml. 

Nickel standard solution, 0. 01 percent. Dissolve 

0. 01 g pure nickel in 10 ml 8 N nitric acid, Dilute 

to 100 ml with water. This solution contains 100 

micrograms per ml. 
Water. Pass tap water through resin demineralizer. See "Special Apparatus." 

Dimethylglyoxime reagent paper. Dip sheets 

of no. 50 Whatman filter paper into ~ 2 percent 

solution of dimethylglyoxime iri acetone at a rate 

faster than the spread of solvent through the paper. 

Pauses must be avoided as they ·cause uneven distribution of the reagent on the paper by allowing the solvent to spread through the paper without the reagent. 

When the paper is dry, repeat the process. Discard 

the outer edges of the paper and cut the dry reagent 

paper into strips 7 /16-in. wide. The reagent paper 

is stable for several months. For more detail on 

preparation of reagent papers, see Clarke and 

Hermance (1938). 

Chromograph. See "Special Apparatus." 

1 gasoline stove. 

1 balance. MiCro torsion type, capacity 25 mg. 

A lucite spoon previously calibrated by weighing a 1 

measurect amount of pulverized plant ash can be used 

in place of the balance to measure samples. 

P~ex culture tubes, 13 by 100 mm, calibrated 

at 2 rnr: · 

Filter sticks. --Alundum filter R. A. 225 sealed 

on end of pyrex glass tube 180 mm long and 7 mm outside diameter. 

1 serological pipette, 0. 5 ml, calibrated in 

tenths of a ml. · 

Rubber bulbs, 10 ml capacity. 

1 glass rod, 150 mm, flattened on one end. 

Platinum dishes, 60 ml. 60 mm diameter and 

30 mm high. 

1 pair tongs, platinum tipped. 

1 fused quartz grating. For support of platinum 

dishes over burner. 

1 test tube rack. 

1 digestion and fusion rack~ See "Special 

Apparatus. 11 

Preparation of standard spot$ 

To a series of test tubes, each· containing 0. 2 ml 

of molybdate solution, 0. 5 ml sodium citrate and 1 

drop of indicator, add respectively 1, 2. 5, 5. 0, 7. 5, 

10. 0, 15. 0, and 20. 0 micrograms of nickel. Adjust 

pH to 8. 8 with 1 + 1 ammonium hydroxide and make 

volume up to 2 ml. Prepare standard spots by passing a 0. 2 ml aliquot 0f each solution through dimethylglyoxime reagent paper in the chromograph. These 

spots correspond respectively to 0. 010, 0. 025, 0. 050, 

0. 075, 0. 10, 0. 15 and 0. 20 percent nickel in the ash 

for a 10 mg sample. 

Proced~re 

Plaee the fresh plant material in a platinum 

dish and ash over the gasoline stove. Stir_ occasionally during the ashing to facilitate burning. After 

glowing ceases, remove from the burner and allow 

the ash to cool. Pulverize the ash with a glass rod 

and mix thoroughly. 

Weigh 10 mg of ash or measure in a spoon and 

transfer to a calibrated culture tube, add 0. 5 ml 

hydrochloric acid and heat in a boiling water bath 

for 20 min. Transfer the culture tube to a rack and 

add 0.2 ml molybdate solution, 0. 5 ml sodium citrate, 

and 1 drop thymol blue. Shake thoroughly and add 

concentrated ammonium hydroxide until the solution 

turns yellow. Then add carefully, one drop at a time, 

the freshly prepared 1+1 ammonium hydroxide to just 

a true blue. If the flakes of carbon remaining from 

the ashing cause confusion in seeing the color of the 

solution, allow the carbon to settle.·out before adding 

more ammonium hydroxide. Increase the volume to 

2 ml with metal-free water, shake thoroughly and 

let stand for about 15 min to allow the calcium citrate 

to precipitate before filtering. To filter, squeeze 

the air out of a rubber bulb, fit it over the open end 

of a filter stick and insert the filter stick into the 

test tube. 

Make a confined spot with 0. 2 ml of the filtered 

solution on reagent paper in the chromograph. For 

details on the operation of the chromograph see page 

18, "Chromographic· determination of nicl}el in soils 

and rocks. • Allow the spots to dry and compare with 

the standard series. 

Determination of Molybdenum in Plants 

The complete method for determination of 

molybdenum in plants is given in U. S. Geological 

Survey Circular 124, (Reichen and Ward, 1951). 

The method is not designed to detect small differences 

in the molybdenum content of plants which are caused 

by such factors as the health of the plant, season, 

and soil moisture. It is, however, sufficiently 

accurate to measure differences which are significant 

in geochemical prospecting. For example,_ as little 

as 0. 25 microgram or 0. 001 percent molybdenum 

can be determined in plant ash. Since the ashing 

process is a means of concentrating the nonvolatile 

qonstituents of a plant, the estimation of a relatively 

large quantity of molybdenum is more frequently 

required than the estimation of a small amount of 

molybdenum. If a 25 mg ash saq1ple is used, 0. 001 

to 0. 020 percent molybdenum can be ·determined, and 

if a 2 mg ash sample is used, as much as o. 25 percent 

molybdenum can be determine~~ If the weight of the 

ash i$ 10 percent of that of the dry material, 0. 25 

percent molybdenum in the ash corresponds to 250 

ppm in the dry material. With the exception of 

vanadium, tungsten, and rhenium, the method is 

practically free from interferences. Under the 

conditions outlined below as much as 200 micrograms 

of ,vanadium in the test solution does not interfere. 

Moreover, tungsten and rhenium are seldom present 

in plants in sufficient quantities to cause ·any 
interference. The field method requires, for the 

most part, simple apparatus and permits the average 

analyst to make 30 or .. more determinations per day. 

Thus, the prospector can obtain the results quickly 

and economically in the field. 

Reagents and apparatus 

Hydrochloric acid, concentrated. 

Hydrochloric acid, 1 N. Dilute 8. 5 ml concentrated acid, sp gr 1. 19, to 100 ml with metalfree water. 

Ammonium. hydroxide, 1 N. Dilute 6. 3 ml · 

concentrated ammonium hydroxide, sp gr 0. 90, 

to 100 ml with metal-free water. 

Lithium nitrate, solid, reagent-grade. 

Potassium nitrate, 10 percent. Dissolve 10 g 

KN03 in water and dilute to 100 ml. 

Potassium thiocyanate, 5 percent. Dissolve 

5 g KSCN in water and dilute to 100 ml. 

Stannous chloride, 10 percent. Dissolve 10 g 

SnC12• 2H20 in lOO ml of 2 N HC1. Filter the 

solution if it is not entirely clear. The addition of 

tin promotes stability, but fresh solutions should 

be prepared weekly. 

Standard molybdenum solution, 0. 01 percent. 

Dissolve 0. 675 g pure Mo03 in a few ml of dilute 

NaOH solution, dilute with metal-free water, make 

slightly acid with hydrochloric acid, and make up 

to 500 ml with metal-free water. This solution 

contains 100 micrograms of molybdenum per ml. 

Standard mol~bdenum solution, 0. 0002 percent. 

Dilute 2 ml of the ~ Ol percent solution to 100 ml 

with metal-free water. Prepare a fresh solution 

daily. 

Phenolphthalein, 1 percent. Dissolve 1 g 

phenolphthalein in 100 ml alcohol. 

Water. Pass tap water through resin demineralizer. See "Special Apparatus. • 

Iso~ropyl ether. Practical or c. P. grades are suita le provided peroxides are absent. Unless 

specially packaged, all dry ether on standing tends 

to fo~m explosive perox~des. Peroxides of isopropyl 

ether interfere with the molybdenum method. To 

test for peroxides shake 5 ml of ether with 5 ml of 

~ acidified aqueous solution of potassium iodide. 

If the iodide solution shows more than a faint yellow 

color, due to free iodine produced by the peroxides, 

the ether contains appreciable quantities of peroxides 

and should not be used. Shake peroxide-free ether 

with 1/10 its volume of equal amounts of stannous 

chloride and potassium thiocyanate solutions on the 

day during which it is to be used. 

1 gasoline stove. 

1 balance, micro torsion type, capacity 25 mg. 

A lucite spoon previously calibrated by weighing a 

measured amourit of pulverized plant ash can be used 

in place of the balance to ·measure samples. 

30 

Pyrex culture tubes, 16 by 150 mm, calibrated 

at 5 ml. 

Dishes, evaporating, 60 ml capacity, platinum. 

1 pair platinum tipped tongs. 

1 fused quartz grating. 

1 test tube rack, capacity 24 culture tubes. 

Glass pestle, pyrex glass rod flattened on one 

end. 

Lucite spoon. A lucite bar with a cavity of 

0. 25 ml, (7 mm diameter, 6. 5 mm deep}, drilled 

near one end. 

1 seroloSiical pi~tte, 1 ml, graduated in tenths 

of a ml. 

1 seroloSiical pipette, 

hundredths of a ml. 

1 ml, graduated in 

1 seroloSiical pieette z 2 ml, graduated in 

halves of a ml. 

1 seroloSiical eipette l 5 ml, graduated in tenths 

of a ml. 

Procedure 

PreSaration of ash. --Ash the fresh plant 

material y heating in a platinum dish over the burner. 

Stir occasionally during the ashing to facilitate burning. After glowing ceases, remove the dish from 

the burner and allow the ash to cool. Pulverize the 

ash with a glass pestle and mix thoroughly. 

Preparation of sample solution. --Weigh 25 mg 

of ash and transfer to a calibrated culture tube. Add 

a spoonful of lithium nitrate (about 0. 1 g) and fuse 

over a low flame holding the mouth of the tube away 

from the operator. Rotate the tube as the melt cools 

to form a thin layer on the sides. Dissolve the melt 

in 1 ml of 1 N hydrochloric acid, add 1 drop of indicator, and add 1 N ammonium hydroxide until the 

solution is faintly pink. Avoid an excess of ammonium hydroxide. ·Dilute to 5 ml with water. 

Preparation of standards. --Pipette the appropriate volumes of the 0. 0002 percent standard solution 

into separate culture tubes to prepare a series of 

standard solutions differing by 0. 5 microgram over 

a range from 0 to 5 micrograms. Add 1 ml potassium nitrate solution to each tube and dilute to 5 ml 

with water. 

Estimation. --To both the standards and the 

plant solutions add 0~ 6 ml concentrated hydrochloric 

acid, 0. 5 ml potassium thiocyanate solution, and 1 

ml stannous chloride solution, shaking after each 

addition. Let the solutions stand f-or about 1 min. 

Make a preliminary comparison of the sample 

solutions with the 5 microgram standard. Discard 

any samples which are obviously dar~er and replace 

with an aliquot of a 10 mg sample of ash prepared 

as follows: 

Fuse the replacement sample with lithium 

nitrate and dissolve the melt in 1 N hydrochloric 
acid as before. Dilute to 5 ml with water. 

Pipette 1 ml (2 mg) of this solution into another 

culture tube, add phenolphthalein,· and then 

1 N ammonium hydroxide until the solution is 

faintly pink. Dilute to .5 ml with water, add 

the concentrated hydrochloric acid, the potassium thiocyanate, and the stannous chloride 

to this aliquot and proceed as below. 

To the standards and the sample solutions add 

1 ml freshly saturated isopropyl ether, cork the 

culture -tube and shake for 15 sec. Within 30 min 

after the extraction, compare the intensity of the 

amber -colored ether layer over the sample solution 

with that obtained over the standard solutions. Use 

a white background to make the comparisons. In 

order to convert the results to ppm, multiply the 

number of micrograms of molybdenum found in the 

25 mg ash s·ample by 40 and in the 2 mg aliquot by 

500. 

APPENDIX 

The minimum quantity of reagents to perform 

1, 000 determinations as well as the desirable stock 

is listed in the table given below. The desirable 

stock (column 4) includes the minimum quantity of 

reagents required and an extra quantity to insure 

against losses resulting from minor accidents and. 

to permit a reasonable number of repeat determinations. The desirable stock is given in units listed 

by supply houses. Unless otherwise specified all 

reagents are analytical grade. Water may be obtained from a public water supply and freed of metals 

by passing it through a resin demineralizer as directed 

under "Special Apparatus." , The quantity of water 

listed in the table is the metal-free water needed for 

the determinations and does not include water for 

washing. 

• 

Reagents required for 1,000 determinations by each method 

Method Reagents 

Heavy metals in Acetic acid, glacial 

water Annnonium hydroxide, cone Carbon tetrachloride 

Dithizone 

Sodium acetate 

Thymol blue, -- sodium salt 

Water, metal-free 

Heavy metals in Annnonium fluoride 

soil or sediment Carbon tetrachloride 

Dithizone 

Hydrochloric acid, cone Hydrochloric acid, cone (Digestion D) 

Nitric acid, cone (Digestion A or B) 

Nitric acid, cone (Digestion C) 

Nitric acid, cone (Digestion D) 

Sodium acetate 

Water, metal-free 

Zinc metal 

Zinc in soils Acetic acid, glacial 

Carbon tetrachloride 

Dithizone 

Hydrochloric acid, cone Potassium bisulfate 

Sodium acetate 

·Sodium thiosulfate, 

Na2S203.5H20 

Water, metal-free 

Zinc, metal 

Nickel in soils and Acetone 

rocks Ammonium hydroxide, 

Dimethylglyoxime 

Filter paper, Whatman no.50, 

sheets diameter 24 em Litmus paper, 100 strip~ 

per vial 

Nickel metal 

Nitric acid, cone Potassium bisulfate 

Sodium citrate 

Water, metal-free 

31 

Actual 

minimun 

6 ml 

30 ml 

10 liters 

.16 g 

8~ g .o g 

10 liters 

350 g 5 liters 

.08 g 

lml 

1 liter 

500 ml 

1 liter 

1.75 liters 

1.75 kg 40 liters 

.01 g 

260 ml 

5.5 liters 

.125 g 1 ml 

250 g 820 g 

500 g 

20 liters 

.1 g 

1 liter 

1 liter 

25 g 

1000 sq in. 

2 vials 

.01 g 

4ml 

~00 g 00 g 

10 liters 

Desirable 

Stock 

1/4 lb 

1/4 lb 

50 lb 

1 g 

1/2 lb 

1 g 

5 gal 

1 lb 

2.5 lb 

1 g 

1 lb 

3 lb 

2 lb 

4 lb 

6 lb 

6 lb 

20 gal 

1/4 lb 

1 lb 

25 lb 

1 g 

1 lb 

1 lb 

3 lb 

2 lb 

10 gal 

1/4 lb 

2 lb 

3 lb 

100 g 

1 pkg 

6 vials 

1 oz 1 lb 

2 lb 

2 lb 

5 gal 
Reagents required for 1,000 determinations by each method.~-Continued 

Method Reagents Actual Desirable 

minimum Stock 

Copper in soils and Acetic acid, glacial 500 _ml : 2 lb . rocks Acetone 1 liter 2 lb 

Annnonium hydroxide, cone 1 liter ~ lb Copper sulfate, CuS04.5H20 .2 g 1 lb 

Filter paper, Whatman no. 50, 

sheets diameter 24 em 1000 sq in 1 pkg Litmus paper, 100 strips 

per vial 2 vials 6 vials 

Potassium bisulfate 500 g 2 lb 

Rubeanic acid (dithiooxamide) 25 g 100 g Sodium citrate 400 g 2· lb 

Sulfuric acid, cone 2 ml l lb 

Water, metal-free 10 liters 5 gal 

Cobalt 1n soils and Cobalt chloride, CoCl2.6H20 .1 g 1 oz rocks Hydrochloric acid, cone 30 ml 1 lb 

Litmus paper, 100 strips 

per vial • 2 vials 6 vials 

2-nitroso-1-naphthol .01 g 5 g Potassium bisulfate 400 g 2 lb 

Sodium citrate (U.S.P.VIII), 

N~C6H~0~.5 1/2 H20 2.5 kg 10 lb 

So um y roxide 120 g 1 lb 

Sodium tetraborate, 

Na2B40 1/4 lb 7 .10HaO 57 g Sulfuric aci , cone .2 ml 1 lb 

Water, metal-free 20 liters 10 gal 

Molybdenum 1n soils Ethyl alcohol, 95 percent 100 ml 1 pint 

and rocks Hydrochloric acid 700 ml 3 lb 

Isopropyl ether, practical ;350 ml 5 lb 

Molybdic anhydride, Moo3 ~075 g 1 oz Phenolphthalein 1 g 1 oz Potassium iodide 10 g 1 oz Potassium nitrate 260 g 1 lb 

Potassium thiocyanate 17.4 g 1/4 lb 

Sodium carbonate 250 g 1 lb 

Sodium hydroxide 1 g 1/4-lb 

Sodium tartrate 232 g 1 lb 

Stannous chloride, 

SnCl2.2H20 60 g 1/4 lb 

Tin metal, mossy 6 g 1/4 lb 

Water, metal-free 20 liters 10 gal 

Lead in soils and Ammonium citrate, (NH4)~C6H507 500 g 2 lb 

rocks Annnonium hydroxide, cone 350 ml 2 lb 

Carbon tetrachloride 10 liters 70 lb 

Chloroform · 1 liter 5 lb 

Dithizone .2 g 1 g Lead nitrate .16 g 1/4 lb '-. 

Nitric acid, cone 1 liter 7 lb 

Potassium cyanide 500 g 2 lb 

Thymol blue, sodium salt .04 g 1 g Water·, metal-free 50 liters 25 gal 

Silver 1n soils and Acetic acid, glacial 5.1 .liters 20 lb 

rocks Ammonium citrate, (NH4)~C6H507 750 g 2 lb 

Annnonium hydroxide, cone 3.1 liters 12 lb 

n-Amyl alcohol, practical 3 liters 6kg p-dimethylaminobenzalrhodanine .01 g 1 g 

Ethyl alcohol, 95 percent, U.S.P. 1 liter 3 pints Litmus paper, 100 sheets 

per vial 10 vials 20 vials 

Nitric acid·, cone 12 liters 42 lb 

Silver nitrate .16 g 1 Oz 

Water, metal-free 50 liters 25 gal 

32 
Reagents requ;ired for ;L:, 000 determinations by each method. --Continued 

Method 

Tungsten in soils 

and rocks 

Readily soluble 

copper, zinc 

and lead in soils 

and rocks 

Zinc in plants 

Nickel in plants 

Molybdenum in 

plants 

Reagents 

Hydrochloric ,acid; cone Isopropyl cethe;r-, pra.ctical Potassium iodide 

Potassium nitrate 

Potassium thiocyanate Sodium carbonate - Sodium chloride 

Sodium tungstate, Na2W04.2H20 

Stannous chloride, ShCl2.2H20 

Water, metal-free 

Acetic acid, glacial Ammonium, citrate, 

(NH4)2HC6H~07 · Ammonium hyaroxide, cone Carbon tetrachloride 

Chloroform 

Copper sulfate, CuS04.5H20 

Dithizone 

Hydrochloric acid, cone Lead nitrate 

Nitric acid, cone Potassium cyanide . Sodium acetate, anhydrous 

Sodium thiosulfate, Na2S203.5H20 

Sulfuric acid, cone Thymol blue, sodium salt 

Water, metal-free 

Zinc metal, 30-mesh 

Acetic acid, glacial Carbon tetrachloride 

Dithizone · Hydrochloric ac·id, cone Sodium acetate, CH3COONa.3H20 . Sodium thiosulfate, N~2S203·SH20 

Water, metal-free 

Zinc metal, 30-mesh 

Acetone 

Ammonium hydroxide, cone Dimethylglyoxime 

Filter paper, Wha tman no. 50, 

sheets diameter 24 em Hydrochloric acid, cone Molybdic anhydride, Mo03 

Nickel metal 

Nitric acid, cone Sodium citrate (U.S.P. VIII), 

Na"3C6H«:)07·5 1/2 H20 

Sodium Jiya.roxide Thymol blue, sodium salt 

Water, metal-free 

Ammonium hydroxide, cone Ethyl alcohol, 95 percent Hydrochloric acid, cone Isopropyl ether, practical Lithium nitrate 

Molybdic a.nhydride, Mo03 ·Phenolphthalein 

Potassium iodide 

Potassium nitrate 

Potassium thiocyanate Sodium hydroxide Stannous chloride, 

SnCl2.2H20 

Tin metal, mossy Water, metal-free 

Actual 

minimum 

4.8 liters 

360ml 

10; g . 125 g . 300 g 625 g . 500 g 

.036 g 480 ·g 20 liters 

60 ml 

fS50 g 

500 mJ 

20 liters 

1 liter 

.2 g 

.2 g 

4ml 

.16 g 

' 4 ml 

500 g so g 

500 g 1.2 liters 

.1 g 

100 liters 

.1 g 

100 ml 

5.5 liters 

.125 g 400 ml 

2 kg 600 g 30 liters 

.01 g 

1 liter 

250 ml 

25 g 

1000 sq in 

250 ml 

2 g 

.01 g 

4 ml 

250 g 

1 g 

.1 g 5 liters 

65 ml 

100 ml 

900 ml 

1.3 liters 

100 g .15 g 

1 g 

10 g 

30 g 32 g 

1 g 

12.~ : 

20 liters 

,, Desirable 

stock 

12 lb ' 

5 lb 

1 oz 1 lb 

1 lb 

2 lb 

2 lb 

1 oz 1 1/4 lb 

10 gal 

1/4 lb 

2 lb 

4 lb 

100 lb 

5 lb 

1/4 lb 

1 g 

1 lb 

1/4 lb 

1 lb 

2 lb 

1 lb 

2 lb 

9 lb 

1 g 

50 gal 1/4 lb 

1 lb 

30 lb 

1 g 

2 lb 

6 lb 

2 lb 

15 gal 1/4 lb 

2 lb 

1 lb 

100 g 

1 pkg 

1 lb 

1/4 lb 

1 oz 1 lb 

1 lb 

1/4 lb 

1 g 

3 gal 

1 lb 

1 pint 

3 lb 

10 lb 

1/2 lb 

1 oz 1 oz 1 OZ · 

1/4 lb 

1/4 lb 

1/4 lb 

1/4 lb 

1/4 lb 

10 gal 

lMaterials listed are for total heavy metals only. Supplemental tests are not included. 

33 
REFERENCES CITED . 

Almond, Hy, and Bloom, Harold, 1951, A semimicro method lor the . determination of cobalt "in 

soils and rocks: a field method using the chromograph: U. S. Geol. Survey Circul;2.r 125, 6 pp. 

Almond, Hy, and Morris, H. T., 1951, Geochemical techniqui s as applied in recent investigations 

in the Tintic d,istrict, Utah: Econ. Geology, vol. 46, 

pp. 608-625. 

Almond, Hy, Stevens, R. E., and Lakin, H. W., 

1951, A confined spot method for the quantitative 

determination of traces of silver in soils and rocks: 

Contributions to Geochemistry, U. S. Geol. Survey 

Bull. In preparation. 

Clarke, Beverly L., and Hermance, H. W., 1938, 

Paper as a medium for analytical reactions. A 

method of applying reagent papers to large volumes 

of solutions: Industrial and Engineering Chemistry, 

'Anal. Ed., vol. 10, pp. 591-600. 

Diehl, Harvey, 1940, The application of the dioximes 

to analyticai chemistry, Columbus, Ohio, The 

G. Frederick Smith Chemical Co. 

Elkins, Harvey B., 1950, The chemistry of industrial toxicology, New York, John Wiley and Sons, 

Inc. , 406 pp. 

Feigl, Fritz, 1946, Qualitative analysis by spot tests. 

Inorganic and organic applications, New York, · 

Elsevier Publishing Co. , Inc. , 574 pp. 

--;-----:-;-' 1949, Chemistry of specific, selective 

and sensitive reactions, New York, Academic 

Press, Inc., 740 pp. 

. Fischer, Hellmut, 1925, Compounds of diphenylthiocarbazone with metals and their use in analysis 

(in German): Wiss. Veroffentlich Siemens-Konzern, 

vol. 4, p. 158. 

Flagg, John F., 1948, Organic reagents us~.:d in 

gravimetric .and volumetric analysis, New York, 

Interscience Publi~hers, Inc., 300 pp. 

Hawkes, H. E., 1950, Geochemical prospecting 

for ores: Applied Sedimentation, edited by 

P. D. Trask, New York, John Wiley and Sons, 

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34 

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m.-DUP. lllc .• lAIII •• o.c. nc••