65T7

Rapid Determination 

of Germanium 

in Coal, Soil 

and Rock

GEOLOGICAL SURVEY BULLETIN 1103 6-B

Rapid Determination 

of Germanium 

in Coal, Soil 

and Rock

By HY ALMOND, HARRY E. CROWK, and CHARLES E. THOMPSON

A CONTRIBUTION TO GEOCHEMISTRY

GEOLOGICAL SURVEY BULLETIN 1036-B

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1955
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

For sale by the Superintendent of Documents, U. S. Government Printing Offlce 

Washington 25, D. C. - Price 15 cents (paper cover)
CONTENTS

Page

Abstract _______________________ _________________________________ 9

Introduction____________ ______ ______ ___________ ____________ 9

General discussion __________ _ ________________________________ 9

Features of the method ____ ___________ __________ ________ __ 10

Reagents and apparatus_ __________ ________________________________ 12

Germanium distillation apparatus. ____ ______________ 12

Procedure _____ ______ _______ ___ _____________ 13

Results________________ ___________________ ___ __________________ 15

Literature cited,__________________________________________________ 16

ILLUSTRATIONS

Page 

Plate 1. Germanium distillation apparatus.... _____ ______ ____ Facing 12

FIGURE 2. Absorption curves. _________________________________ . _ 11

3. Erlenmever wash bottle before and after modification-______ 13

m

A CONTRIBUTION TO GEOCHEMISTRY

RAPID DETERMINATION OF GERMANIUM IN COAL, 

SOIL, AND ROCK

Bv HY ALMOND, HARRY E. CROWE, and CHARLES E. THOMPSON

ABSTRACT

Cluley's colorimetric method for the determination of germanium in coal with 

phenylfluorone is modified to speed up the rate at which coal samples can be 

analyzed. The method is also adapted to the determination of germanium in 

soils and rocks. To avoid the time-consuming step of neutralizing after the 

alkaline fusion, as described by Cluley, coal samples are ashed at 550° C. Soils 

and rocks are decomposed with hydrofluoric acid and the residue is fused with 

a mixed flux of potassium bisulfate and persulfate. The germanium in the coal 

ash or in the fusion product is then dissolved in 1+1 hydrochloric acid and distilled on a specially designed distillation rack, on which six samples can be distilled at once.

Although the maximum absorbance of the germanium phenylfluorone complex 

was found to be between 500 and 505 m/* (millimicrons), the absorption is measured at 510 m,u to minimize interference by reagent. However, visual comparison 

with standards is preferred to the instrumental method of estimation. A sensitivity of 2 ppm (parts per million) germanium in the coal and 1 ppm in soils or 

rocks is obtained. About 50 coal samples can be analyzed per man-day.

INTRODUCTION

GENERAL DISCUSSION

The growing importance of germanium in the electrical industry 

has led to the search for germanium in coal as well as in other material. As part of a geochemical study of the occurrence of minor 

elements, including germanium, in American coals, Stadnichenko, 

Murata, Zubovic, and Hufschmidt (1953) reported values obtained 

spectrographically. Fleischer (written communication, 1954) collected 

data on the germanium content of igneous and sedimentary rocks. 

To supplement these studies a colorimetric method for the determination of germanium in coal, soils, and rocks was begun largely through 

the inspiration and suggestions of Stadnichenko and Zubovic.

The simplest method of decomposing coal is by ashing the coal 

sample, but Goldschmidt (1937) and Morgan and Davies (1937) report losses of germanium during the ashing process. Cluley (1951) 

decomposed coal by fusing the sample with a sodium carbonatenitrate flux More recently Aubrey and Payne (1954) and Waring 

and Tucker (1954), using more reliable methods of analyses than that

347502° 55 9
10 CONTRIBUTIONS TO GEOCHEMISTRY

used by the earlier workers, found little or no losses of germanium 

during the ashing process.

Aitkenhead and Middle ton (1938) decomposed minerals with hydrofluoric, nitric, and sulfuric acid, and Hyblinette and Sandell (1942) 

used these acids to decompose silicate rocks.

Phenylfluorone, first described by Cluley for the determination of 

germanium, reacts with many elements, but by distilling from 1 + 1 

hydrochloric acid Cluley was able to separate germanium from the 

interfering elements.

In the procedure described here for germanium in coals, soils, and 

rocks, Cluley's method is greatly simplified to provide the rapid and 

cheap results needed for a geochemical program. 

FEATURES OF THE METHOD

Coal samples are decomposed by ashing in a muffle furnace starting 

at a temperature below 300° C, raising the temperature to 550° C, 

and maintaining at the latter temperature for about 1 hour. The 

ash samples are ready for distillation of germanium tetrachloride 

without neutralization of the solution as required in the technique 

described by Cluley.

Soil or rock samples are decomposed by eliminating a large amount 

of the silica with hydrofluoric acid, followed by fusing the residue 

with a mixture of potassium bisulfate and persulfate. This flux, 

when heated with the residue from the hydrofluoric acid treatment, 

drives off fluorides and oxidizes sulfides; the latter, if present, might 

prevent the quantitative distillation of germanium tetrachloride. 

This treatment is more rapid than the acid digestions used by Schneider 

and Sandell (1954). Alkaline fluxes are not used because large quantities of dissolved silica are introduced into the solution which prevent 

the quantitative distillation of germanium tetrachloride, as previously 

reported by Aitkenhead and Middleton (1938).

Separation of germanium from interferences by distillation with 

hydrochloric acid has been described by Cluley and many other 

workers. The unique feature presented here is an engineering one. 

A rack supporting six stills is designed to carry out six distillations 

at the same time (pi. 1). The volume of acid in each still has been 

decreased so that distillation time required is only 15 minutes for 

each group of six distillations.

Cluley's procedure for estimation of germanium with phenylfluorone also has been modified. The acidity of the solution has 

been changed from 1.15 N, used by Cluley, to 0.6 N to increase the 

sensititivy. The effect of acidity in absorption of the germanium 

phenylfluorone complex is tabulated below. The results, verifying 

a similar study made by Cluley, show that the 0.6 N solution is more 

sensitive than the more acid solution.
RAPID DETERMINATION OF GERMANIUM 11

Effect of acidity on absorption of germanium phenylfluorone complex in 10 ml of 

solution, containing 1 microgram Ge.

Normality 

of solution

0. 2 

. 38 

. 62

1. 0 

1. 1

0. 145

. 140

. 116

. 117

. 112

. 105

Absorptiometric studies, carried out with a Beckman D. U. spectrophotometer, showed that the germanium phenylfluorone complex 

adsorbed maximally between 500 and 505 m,u, whereas the reagent 

adsorbed maximally between 450 and 460 m^ (fig. 2). In the proposed method, readings are taken at 510 in/u, where there is little 

absorption by reagent to interfere with the determination. Adherence 

to Beer's law is good between 0.1 and 1 microgram of germanium per 

ml of solution.

As the absorption of reagent varied somewhat with acid concentration (see Cluley, 1951, table 3), the acid concentration of the 

sample solution was kept essentially the same as the solution from 

which the original standard curve was prepared. In the instrumental method described here, with each set of unknown solutions 

analyzed, a new curve is established with 3 standard germanium 

solutions, that is, 0, 1.0, and 5 micrograms of germanium per 10 ml 

of final solution.

1.8

1.6- 

1.4- 

1.2-

I

coO.8-

06- 

0.4- 

0.2-

A - Reagent 

B- Reaction product af 

50 r Ge and reagent

430 440 450 460 470 480 490 500 510 520 530 540 550 560 

WAVE LENGTH (my)

FIGURE 2. Curves showing absorption by reajrenl (.1) and of a reaction product (B).
12 CONTRIBUTIONS TO GEOCHEMISTRY

Visual comparison with standards is preferred because of greater 

sensitivity and because a new curve must be run each time the 

instrument is used due to variable absorption of the reagent itself. 

As little as 0.2 microgram of germanium can be detected in an aliquot 

of the distillate. A standard series ranging from 0.2 to 3 micrograms of germanium is prepared at the same time that aliquots of the 

distillates are prepared for final color development. After proper 

adjustment of the acidity of each solution and addition of necessary 

reagents, the color develops on standing. Visual comparison of 

unknown solutions with the standard series is made any time after 

1 hour, but should be done within 3 hours, because precipitation of 

the germanium phenylfluorone complex takes place on prolonged 

standing.

REAGENTS AND APPARATUS

Phenylfluorone. Dissolve 0.03 g in 85 ml ethyl alcohol and 5 ml (1 + 6) sulfuric 

acid by warming on a steam bath, then dilute to 100 ml-with ethyl alcohol.

Gum arabic. Add 0.05 g to 100 ml water and warm until in solution.

Potassium bisulfate, potassium persulfate fusion mixture. Mix equal weights of 

these two reagents.

Hydrochloric acid, cone, reagent grade.

Hydrochloric acid (1 + 1). To 2 liters of metal-free water add 2 liters of concentrated hydrochloric acid.

Hydrochloric acid, approximately 0.05 N. Dilute 8.3 ml of 1+1 hydrochloric acid 

to I liter.

Hydrofluoric acid, J^8 "percent.

Litmus paper.

Standard germanium solution, 0.01 percent. Dissolve 0.144 g of germanium dioxide in 20 to 25 ml of 0.1 N sodium hydroxide and dilute to 1 liter. This 

solution has 100 micrograms of germanium per ml.

Culture tubes, 16X150 mm. Marked at 10 ml.

Cylinders, graduate, 25 ml, borosilicate.

Stirring rod, borosilicate glass.

Pipets, 1, 5, 10 ml graduated.

Sieve, 80 mesh.

Mortar and pestle, mullite.

Platinum crucible, 45-ml capacity.

Furnace, muffle; thermostatically controlled.

Aluminum dishes. Made from aluminum foil (may be used for containers to hold 

coal during ashing).

GERMANIUM DISTILLATION APPARATUS

A 2-shelf rack supporting 6 distillation units, germanium still, as 

shown in plate 1. Each distillation unit consists of the following:

Erlenmeyer wash bottle, figure 3A. Modified as in figure 3-B. The tubing at position A is bent into a U-shape. At position B and C the glass tubings are 

cut off and sealed.

Tygon tubing. Six-inch piece of tygon tubing is connected at position D (fig. 3b).
GEOI.Or.ICAL SURVEY BULLETIN 1036 PLATE 1

GERMANIUM DISTILLATION APPARATUS

RAPID DETERMINATION OF GERMANIUM 13

Glass tubing. Six-inch piece of glass tubing is connected to the tygon tubing. 

Rubber stopper, number 3. Insert the glass tubing of item 3 into a 1-hole rubber

stopper so that 2.5 inches of glass tube extends beyond the base of the rubber

stopper. 

Condenser, 20-mm length. Place the rubber stopper of item 4 into the condenser.

The 2.5 inches of glass tube beyond the base of the rubber stopper extends to

the position where cooling takes place in the condenser. 

Graduated cylinder, 25 ml. Place at outlet of the condenser in position to collect

distillate. 

Burner, alcohol, glass, 4-oz capacity.

PROCEDURE

Decomposition of coal. Transfer a 0.5-gram coal sample, previously 

ground to pass through an 80-mesh sieve, to a platinum crucible or 

aluminum dish. Place in a muffle furnace at temperature below 300° 

C. Raise the temperature in increments of 50° to a temperature of 

550° C. Allow to remain at 550° for about 1 hour. Remove from 

the furnace and allow samples to cool. Transfer the ash to the Erlenmeyer distilling flask, then add about 15 ml hydrochloric acid (1 + 1).

A B

FIGURE 3. Erlenmeyer wash bottle before modification (A) and after modification (B).

Decomposition of soil or rock. Grind the soil or rock to pass through 

an 80-mesh sieve. Thoroughly mix and transfer a 2.0-gram representative sample to a platinum crucible. Add about 20 ml of hydrofluoric 

acid to the crucible and mix with the sample. Evaporate to dryness 

on the steam or hot water bath. Add about 2.5 grams of potassium 

bisulfate, persulfate fusion mixture and fuse to a clear melt. Allow to 

cool. Add about 5 ml of 1 +1 hydrochloric acid. Break up the flux 

in the cold, then transfer the contents of the crucible to the Erlen-
14 CONTRIBUTIONS TO GEOCHEMISTRY

meyer distilling flask. Wash the crucible with 5-ml portions of 1 +1 

hydrochloric acid three times, adding the washings to the distilling 

flask.

Distillation. Connect the distilling flask in the distilling apparatus, 

light the alcohol burner, turn on the water condenser, and collect about 

10 ml of distillate in the graduated cylinder. Record the volume of 

distillate. Avoid any possible contamination with iron. To do the 

maximum number of determinations in a work day, carry out distillations in groups of six. About 30 to 50 distillations can be made per 

man-day.

Color development. About 2 hours before the end of the work day, 

begin the operations for color development of standards and unknowns 

for visual or for photometric estimation, whichever is preferred. 

Transfer exactly 1 ml of distillate to a culture tube. Add 1 ml of gum 

arabic, then dilute to 10 ml with water. Add exactly 0.5 ml of phenylfluorone reagent, stopper with a cork stopper and shake several times 

to insure good mixing. Allow to stand about 1 hour, but less than 3 

hours, then compare unknowns with the standard series prepared at 

the same time or with a standard curve.

Standards for visual estimation. To a series of culture tubes add 0, 

0.2, 0.4, 0.6, 1.0, 1.2, 1.5, 2.0, and 3.0 micrograms of germanium, 

respectively, from standard solutions. Add about 1 ml of water and 

just neutralize with 0.05 N hydrochloric acid, testing with litmus paper. 

Add exactly 1 ml 1 + 1 hydrochloric acid and proceed as described 

under "Color development," beginning with "addition of 1 ml of gum 

arabic."

Standards for photometric estimation. To a series of culture tubes 

add 0, 0.5, 1.0, 2.0, 4.0, 8.0, and 15 micrograms of germanium, respectively, from standard solutions. Neutralize with 0.05 N hydrochloric 

acid, testing with litmus paper. Add exactly 1 ml of 1 + 1 hydrochloric acid and proceed as described under "Color development" 

beginning with "addition of 1 ml of gum arabic." After 90 minutes 

determine the absorbance at 510 m/z of each solution. Plot the micrograms of germanium against the absorbance.

With each set of distillates carried through the color development 

operation, prepare a set of 0-, 1.0- and 5.0-mierogram standards in 

culture tubes and carry these standards through the color development. 

Determine the absorbance of standards and unknown solutions. 

Check the three absorbances of the standard solutions with the standard curve and, if necessary, prepare a new absorption curve. This 

may be necessary because absorbance varies with concentration of 

reagent or acidity of solution or both.

Measurement. Estimate the germanium content of the unknown 

solution visually by comparison with standards or with a spectro-
RAPID DETERMINATION OF GERMANIUM 15

photometer by comparison with a standard absorbance curve prepared 

at 510 m/i wave length.

Calculation. The calculation of parts per million (ppm) of germanium in the original sample may be done simply by application of 

the following formula:

^ , . Ge (ppm)=ml of distillateXmicrograms found in the aliquot

 - | - 

wt of sample

RESULTS

Results of colorimetric determinations on coal samples are compared 

with spectrographic results below.

Comparison of duplicate determinations of germanium in coal by the colorimetric 

method and by the spectrographic method

Sample no.

1

2

3

4

5

6

7

g

10

 Q

12

13_ __ ___ _ ____ _ _______ __._

14

15

16- _

17

18

19

20

21

22

23__

Germanium (ppm)

Colorimetric method (Visual comparison)

40 

0 

5 

13 

0 

12 

25 

22 

0 

14 

7 

165 

29 

27 

12 

33 

, 9 

2 

12 

3 

36 

15 

12 

4

2 40 

2 0 

2 3 

2 17

2 1 

2 11 

2 23 

2 28 

2 0 

2 25 

2 14 . 

2 135 

26 

30 

7 

34 

10 

1. 3 

11 

2 

32 

12 

10 

3. 2

Spectrographic 

method 1

42 

0 

6 

8 

3 

12 

30 

21 

0 

10 

8 

134 

34 

44 

12 

50 

12 

4. 5 

21 

3. 9 

20 

25 

23 

7. 6

1 Spectrographic analyses by K. J. Murata and Elizabeth Hufschmidt, U. S. Geological Survey.

2 Only 0.2-gram samples used for analyses.
16 CONTRIBUTIONS TO GEOCHEMISTRY

Of the 24 samples used, serious variations in results by the two 

methods of analysis were found in only 4 samples (19, 21, 22, and 23). 

As these samples were not finely ground, they may not have been of 

uniform composition.

In soils and rocks the method for the determination of germanium 

was tested in two ways. First, various known amounts of germanium 

were added to 0.1-gram fractions of a well mixed soil. Their recoveries 

were as follows:

Recovery of germanium added to soil

Oe 

added 

(micrograms)

0

2. 0

4. 0

8. 0

15. 0

30.0

Oe 

recovered 

(micrograms)

0.9

2.8

4. 7

9.2

13.0

31. 1

Second, the method was tested by comparing results obtained by 

the colorimetric method with those obtained spectrographically. The 

results were as follows:

Comparison of colorimetric and spectrographic results on three soil or rock samples 

(Germanium content in ppni)

Spectrographie analyses by A. T. Myers, U. S. Geological Survey.]

Colorimetric by 

Sample no. visual comparison Spectrographie

25 1, 200 I, 700

26 180 190

27 24 30

Although sample 26 is high in sulfides, the results compare as favorably with the spectrographic method as those for samples 25 and 27. 

There is a tendency for the colorimetric to be a little lower than the 

spectrographic results, perhaps because not quite all of the germanium 

is distilled in the brief distillation period. By distillation of larger 

volumes of hydrochloric acid or by use of smaller samples, better 

recoveries can be made, but the method as described gives suitable 

recoveries for the geochemical study of trace amounts of germanium.

LITERATURE CITED

Aitkenhead, W. C., and Middleton, A. R., 1938, Determination of germanium in

minerals and solutions: Indus, and Eng. Chemistry, Anal, ed., v. 10, p.

633-635. 

Aubrey, K. V., and Payne, K. W., 1954, Volatilization of germanium during the

ashing of coal; Fuel, v. 33, p. 20-25. 

Cluley, H. J., 1951, Determination of germanium, Part II: Absorptiometric

determination with phenylfluorone; Part III: Determination in flue dust,

coal and coke: Analyst, v. 76, p. 523-536.
RAPID DETERMINATION OF GERMANIUM 17

Goldschmidt, V. M., 1937, The laws of the geochemical distribution of the elements: Chem. Soc. London Jour., p. 655-675. 

Hyblinette, A. G., and Sandell, E. B., 1942, Determination of germanium in

silicate rocks: Indus, and Eng. Chemistry, Anal, ed., v. 14, p. 715-716. 

Morgan, Gilbert, and Davies, G. R., 1937, Germanium and gallium in coal ash

and flue dust: Chemistry and Industry, p. 717-721. 

Schneider, William A., Jr., and Sandell, E. B., 1954, Photometric determination

of traces of germanium after carbon tetrachloride extraction: Microchimica

Acta, Heft 2, p. 263-268. 

Stadnichenko, Taisia, Murata. K. G. T Zubovic, Peter, and Hufschmidt, E. L.,

1953, Concentration of germanium in the ash of American coals, a progress

report: U. S. Geol. Survey Circ. 272. 

Waring, Claude L., and Tucker, Wendell, P., 1954, Effect of ashing temperature

on the volatility of germanium in low-rank coal samples: Anal. Chemistry,

v. 26, p. 1188-1199.

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