Colorimetric 

Determinations of 

Traces of Bismuth 

in Rocks

GEOLOGICAL SURVEY BULLETIN 1036-1

Colorimetric 

Determinations of 

Traces of Bismuth 

in Rocks

By F. N. WARD and H. E. CROWE

CONTRIBUTIONS TO GEOCHEMISTRY

GEOLOGICAL SURVEY BULLETIN 1036-1

A rapid method of determination 

devised primarily for use in 

geochemical exploration

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956
UNITED STATES DEPARTMENT OF THE INTERIOR 

Fred A. Seaton, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

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

Washington 25, D. G. - Price 15 cents (paper coyer)
CONTENTS

Page

Abstract_____________________________________ 173

Introduction-.____________________________________________________ 173

Experimental work._______________________________________________ 175

Reagents and apparatus____________________________________________ 176

Procedure. ____________________________________ 176

Results________________________________________ 177

Literature cited.________________________________________________ 178

in

CONTRIBUTIONS TO GEOCHEMISTRY

COLORIMETRIC DETERMINATIONS OF TRACES OF 

BISMUTH IN ROCKS

By F. N. Ward and H, E. Crowe

ABSTRACT

A rapid method for determining traces of bismuth in rocks has been devised 

primarily for use in geochemical exploration. The method is based on the reaction 

of bismuth with carbamate in a cyanide medium and subsequent extraction of 

the yellow complex with chloroform. The proposed procedure is applicable to 

rocks containing from 10 to 300 parts per million (ppm) of bismuth, and only 

slight modifications are necessary to extend the range upward. For two different 

rocks the confidence limits at the 95-percent level calculated from the mean 

values of 13.8 and 107.0 ppm obtained by 5 repeat determinations are respectively 

±1.4 and ±3.4 ppm.

INTRODUCTION

A rapid method for determining traces of bismuth in rocks was 

needed in the Geological Survey to analyze several hundred rock 

samples to establish possible geochemical dispersion patterns of 

bismuth, which in turn might be useful in the exploration for bismuth 

mineralization. To date practically all trace determinations of bismuth 

in soils and rocks have been made with spectrographic procedures 

(Ahrens, 1945). The spectrographic determination of bismuth is 

normally good, although the procedure requires a moderately expensive spectrograph and a trained technician; for a routine geochemical 

exploration laboratory, however, a chemical method requiring neither 

specialized equipment nor trained specialists seemed highly desirable.

Traces of bismuth in such metals as antimony, mercury, silver, 

iron, and copper are usually determined by its reaction with dithizone 

in an acid medium (Sandell, 1950; Snell and Snell, 1949). Traces of 

bismuth in lead are collected by a hydroxide precipitation and subsequently determined by the reaction with potassium iodide (Robinson, 1939). Traces of bismuth in biological materials have been 

determined by either the iodide or the dithizone reaction.

Small amounts of bismuth in dilute sulfuric acid react with an 

excess of iodide to form a yellow complex that can be extracted by 

higher alcohols and esters, but attempts to apply the iodide method 

to the determination of bismuth in rocks were unsuccessful. Platinum, 

palladium, antimony, and tin also react with iodide yielding yellow

398774 56 173
174 ICONTEIBUTIONS TO GEOCHEMISTEY

or rose-colored products (Sandell, 1950). Moreover, oxidizing agents 

liberate iodine from the iodide and the color of a dilute aqueous 

solution of iodine resembles that of the bismuth complex. Reducing 

agents such as sulfite and ascorbic acid prevent the formation of 

iodine until they are exhausted, but in a system as complex as a 

rock-sample solution the maintenance of reducing conditions in air 

becomes impracticable.

Methods for determining bismuth based on dithizone reactions are 

not easily applied to rocks because of the difficulty of separating lead 

from bismuth. The dithizonates of both elements are extracted under 

similar conditions, and the separation is based on the comparative 

stability of the bismuth dithizonate at a pH of less than 3 or by 

successive extractions of the organic solvent containing the dithizonates with portions of a phthalate buffer. The phthalate buffer 

preferentially decomposes the lead complex, leaving most of the 

bismuth in the organic phase.

Tompsett (1938) observed that bismuth reacted with diethyldithiocarbamate to form a complex extractable by ether from a weak 

acid solution. Strafford, Wyatt, and Kershaw (1945) and LaCoste, 

Earing, and Wiberley (1951) observed that chloroform also extracted 

the complex. Later Sedivec and Vasak (1950) and Cheng and Bray 

(1953) reported that bismuth was the only element causing interference when carbamate and ethylenediamine-tetraacetic acid were 

used to determine copper colorimetrically, and that cyanide destroyed 

copper carbamate but did not affect bismuth.

These observations provide a basis for determining traces of 

bismuth in rocks after preparing a suitable sample solution. Briefly, 

a pyrosulfate fusion of the rock sample is treated with hot moderately 

concentrated nitric acid. After addition of solid disodium ethylenediaminetetraacetic acid (EDTA), ammonia is added until the pH is 

about 6. The insoluble residue after the sample attack is removed by 

filtration, and, in the presence of cyanide, the bismuth carbamate 

complex is formed. Extraction of the complex with a small volume of 

chloroform concentrates it so that the yellow color is easily observable.

Cheng, Bray, and Melsted (1955) developed a method for determination of bismuth based on its reaction with carbamate and used the 

method to determine the element in lead-bass alloys. They dissolved 

EDTA in an aqueous solution of cyanide and used the mixtire to 

complex iron, aluminum, and other interfering elements which precipitate when the acidic bismuth sample is made alkaline. The 

quantity of interfering elements present governed the amount of 

EDTA required, but an excess did not interfere.
'COLORIMETRIC DETERMINATIONS OP BISMUTH 175 

EXPERIMENTAL WORK

The present authors considered that varying the amount of EDTA 

added with the quantities of interfering elements present often 

unknown was not feasible in routine work. They therefore selected 

a tactite containing 200 ppm of bismuth determined spectrographically, and relatively large amounts of iron, aluminum, and other 

metals to use in determining experimentally the quantities of EDTA 

necessary to react with the interfering elements. One-half gram 

portions of the tactite were fused with pyrosulfate and treated with 

dilute nitric acid. The duplicate results obtained by adding various 

amounts of EDTA to the dilute nitric acid solution of the sample are 

given as follows:

Effect of disodium ethylenediaminetetraacetic acid (EDTA) on 

determination of bismuth

EDTA added, grams Bismuth found, ppm

0.25________________________________ 28 20

1.0____________________________________ 190 225

1.5_______ ______________________ 200 225

2.0____________________________________ 190 225

In all the work reported here, solid EDTA and an aqueous cyanide 

solution are added separately to the sample solution in place of the 

mixture recommended by Cheng, Bray, and Melsted (1955), because 

the mixture prepared by the authors turned brown and became 

ineffective in less than two hours. The reagents were effective if 

added separately.

Because certain rock samples contained appreciable amounts of 

copper, experiments were made to determine how much copper could 

be tolerated in the proposed procedure. Various amounts of copper 

and 100 micrograms of bismuth were added to five 0.50 gram portions 

of a bismuth-free rock and the portions were taken through the entire 

procedure. The results are shown as follows:

Determination in micrograms, of added bismuth in presence of copper

Bismuth added Copper added Bismuth found

100 0 101

100 100 95

100 1000 95

100 5000 90

100 10000 88

The recoveries of the added bismuth show that up to 2 percent of 

copper in the original sample can be tolerated. Higher concentrations may cause erratic results simply because of the failure of the 

cyanide to break up the copper carbamate complex.
176 CONTRIBUTIONS TO GEOCHEMISTBY

REAGENTS AND APPARATUS

[All chemicals are Reagent Grade]

Ammonium Hydroxide, sp. gr. 0.90.

Bismuth Standard A. Dissolve 0.5 gram bismuth metal in 500 ml concentrated

nitric acid. Solution contains 1000 micrograms per ml. 

Bismuth Standard B. Dilute 1 ml of standard A to 100 ml with water. Solution

contains 10 micrograms per ml in 1:100 nitric acid (.16N). 

Chloroform, C. P. boiling range Min. 95 percent between 59.5 and 61.5° C. 

Disodium ethylenediaminetetraacetic acid (EDTA). 

Nitric acid, 8 molar. 

Potassium pyrosulfate. 

Sodium cyanide, 5 percent aqueous.

Sodium diethyldithiocarbamate, 1 percent aqueous solution. 

Bottle, dropping, 30 ml capacity. 

Beakers, Pyrex, 60 ml capacity. 

Cotton, absorbent. 

Filter paper, 9 cm Whatman No. 1. 

Funnels, filter, diam. 4.5 cm. 

Funnels, separatory, 60 ml, Squibb type. 

Pipette, graduated, 1 ml capacity. 

Pipette, graduated, 5 ml capacity. 

Pipette, volumetric, 1 ml capacity. 

Photometer.

pH .test paper, range 1-6.

Tubes, or cuvettes, for absorbance measurements. 

Balance, sensitivity 2 mg or better.

PROCEDURE

Fuse 0.5 gram of finely powdered rock sample with 1.5 gram of 

potassium pyrosulfate in a 60 ml beaker. Cool and add 2 ml of 8 

molar nitric acid. Boil for about 0.5 minute. Add 8 ml water and 

again heat until solution boils gently. Cool and add 2 grams solid 

EDTA. Stir for 10 to 15 seconds and add concentrated ammonium 

hydroxide drop by drop until pH is 5 to 6. Test externally with pH 

test paper. Add 5 ml sodium cyanide solution and filter, collecting 

filtrate in a 60 ml separatory funnel. To the filtrate add 1 ml concentrated ammonium hydroxide, 1 ml of carbamate reagent, and 5 ml 

of chloroform. Shake the funnel and contents 1 minute. Drain 

organic layer into a tube or cuvette through a piece of cotton inserted 

in the funnel stem and read absorbance at 400 millimicrons. From 

a previously established standard curve, read the number of micrograms of bismuth present. Double the results to convert to parts 

per million.
COLORIMETRIC DETERMINATIONS OP BISMUTH 177 

RESULTS

Although many methods useful in geochemical exploration do not 

require complete break-up of the rock sample, the easy solution of the 

major part of the constituent being determined is definitely advanr 

tageous. With the silicated limestones, which comprise most of the 

materials studied in this paper, the advantage is apparently realized, 

allowing good results to be obtained by the colorimetric method.

The good agreement between the spectrographic and the colorimetric method is indicative of the accuracy of the latter method when 

applied to the types of materials included in this paper. ^

Determination of bismuth in rocks by spectrographic and colorimetric methods

Bismuth, ppm ' 

Laboratory No.

54-3613

3633

3635

3652

3657

3671

3711

3712

Field No.

WH-3

23

25

42

47

61

101

102

Spectrographic 

method

50

80

10

40

50

200

100

60

Colorimetric 

method

68

119

17

55

40

225

115

95

The recovery of added bismuth by the proposed method was tested 

by adding various amounts of soluble bismuth to 0.5 gram portions of 

2 rock samples of known bismuth content and taking the portions 

through the entire procedure, starting with the pyrosulfate fusion. 

The results are tabulated below.

Recovery, in micrograms of added bismuth 

Laboratory No. Field No. Present 

54-3796 WH-185 5

54-3795 WH-184 14

Added

10

20

30

40

50

80

100

10

20

30

40

50

80

100

Found

16

26.5

35

45

54

85

104

22.5

31.5

44

52.5

60

87

102.5

Recovered

11

21.5

30

40

49

80

99

8.5

17.5

30

38.5

46

73

88.5
178 CONTRIBUTIONS TO GEOCHEMISTRY

The amounts of bismuth found in the separate portions are shown 

in the 5th column, and the amounts recovered in the last column.

The accuracy of a useful method in geochemical exploration need 

not be great, but the precision or "repeatability" must be good. 

The repeatability of the proposed method was tested by making 5 

separate determinations on 5 different samples. The results are 

shown below.

From the data shown in the table below the standard deviation 

and the confidence limits at the 95 percent level were calculated in 

the manner given by Youden (1951). The data show that, within 

the concentration range covered, the repeatability is good.

The proposed bismuth method is relatively simple, rapid, precise, 

and moderately accurate. A laboratory technician can determine 

traces of bismuth in more than 30 rock samples during an 8-hour 

day to provide data adequate for elimination of background materials and for the establishment of values useful in systematic investigation of the bismuth content of rocks relative to geochemical 

exploration.

Repeatability of bismuth determinations 

[St. D.=Standard deviation]

Laboratory 

number

54-3635 - 

3652 ... 

3613 .- 

3633 .-.

3711 _

Field number

WH-25 - 

42. ....

3 .....

23..... 

101 . 

Bismuth, ppm, in run 

1

15 

42 

87 

105 

125

2

13 

42 

82 

105 

121

3

13 

38 

85 

110 

125

4

13 

44 

85 

110 

125

5

15 

42 

85 

105 

125

Mean

13.8 

41.6 

84.8 

107.0 

124.2

St. D.

1.095 

2.19 

1.79

2.74 

1.79

95 percent 

level

±1.4 

±2.7 

±2.2 

±3.4 

±2.2

LITERATURE CITED

Ahrens, L. H., 1945, Trace elements in clays: South African Jour. Sci., v. 41, 

p. 152.

Cheng, K. L., and Bray, R. H., 1953, Two specific methods for determining 

copper in soil and plant material: Anal. Chemistry, v. 25, p. 655-658.

Cheng, K. L., Bray, R. H., and Melsted, S. W., 1955, Spectrophotometrie determination of bismuth with sodium diethyldithioearbamate: Anal. Chemistry, 

v. 27, p. 24-26.

LaCoste, R. J., Earing, M. H., and Wiberley, S. E., 1951, Colorimetrie estimation of various metal derivatives of sodium diethyldithioearbamate: Anal. 

Chemistry, v. 23, p. 871-874.

Robinson, R. G., 1939, Rapid determination of traces of bismuth in lead: Analyst, 

v. 64, p. 402.

Sandell, E. B., 1950, Colorimetrie determination of traces of metals, 2d ed., 

New York, Interscienee Publishers, Inc., 673 p.
COLORIMETRIC DETERMINATIONS OP BISMUTH 179

Sedivec, V., and Vasak, V., 1950, The use of complexons in chemical analysis IX. 

The colorimetrie determination of copper by sodium diethyldithiocarbamate: 

Collection Czechslov. Chem. Communs., v. 15, p. 260-266.

Snell, F. D., and Snell, C. T., 1949, Colorimetrie methods of analysis, 3d ed., 

New York, D. Van Nostrand Co., Inc., 950 p.

Strafford, N., Wyatt, P. F., and Kershaw, F. G., 1945, Scheme for the photometric determination of minute amounts of arsenic, copper, lead, zinc, and 

iron (with certain other metals) in organic compounds, e. g., medicinals: 

Analyst, v. 70, p. 232-246.

Tompsett, S. L., 1938, Determination of bismuth in biological materials: Analyst, 

v. 63, p. 250-252.

Youden, W. J., 1951, Statistical methods for chemists, New York, John Wiley 

and Sons, p. 12.