October, 1923
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Bureau of Mines, Pittsburgh, Pa., for examination. He found that there was a third substance present in the melts, but owing to the high refractive indices of all the substances, it was not possible to make quantitative comparisons.
APPLICATION OF THE DATA The data can be applied to the analysis of mixtures of tetryl and picric acid in the manner described in the paper dealing with mixtures of T X T and tetryl.2 However, it is difficult to use this method within the concentration range 44 to 63 per cent of tetryl, because of the difficulty in obtaining accurate checks and the peculiarities of this portion of the curve. The difficulty in obtaining accurate checks may be ascribed to the fact that the supercooled mixtures 4 are rather viscous. Thick suspension of air bubbles is quickly TIME OF HEATING, MINUTES formed when the melt is stirred, and this prevents an even FIG.8 - c U R V E SHOWING RISEI N TEMPERATURE AS MIXTURES OF TETRYL rate of heat transference, so that the uneven rate of cooling AND PICRIC ACIDARE HEATEDAT UNIFORM RATES under the best of conditions yields results that are not within the usual range of accuracy. From this it would appear that the compound formed conACKNOWLEDGMENT sists of one molecule of tetryl and one molecule of picric The writers wish to express their appreciation of the many acid, as the others are outside the concentration range covered helpful suggestions on the interpretation of the data given by the flat portion of the curve. Melts of the pure components and various melts of these by R. E. Hall, physical chemist of the Pittsburgh Experitwo were submitted to W. M. Myer, petrographer of the ment Station, Bureau of Mines.
T h e Separation of Tin from Other Metals’ Including Its Determination after Precipitation by Means of Cupferron By N. Howell Furman PRINCETON UNIVERSITY, PRINCETON, N. J.
Kling and Lassieur haae proposed the use of cupferron as a precipitant for quadritralent tin. This method has been studied in detail, and found to be rapid, conaenient. and accurate. I t is especially suitable in connection with the analysis of tin-antimony alloys by the McCay method. A n alternate electrolytic method which Kling and Lassieur recommend highly has not been found to be satisfactory for the rapid determination of tin.
Attention has been called to a widespread serious misunderstanding of the conditions which are necessary for the separation of antimony from tin in dilute hydroj7uoric acid solutions. B y means of established methods, together with some additional ones here described, tin may be separated from copper, lead, arsenic, antimony, bismuth, cadmium, zinc. manganese, cobalt, and nickel.
EARLY all the metallic elements which are commonly associated with tin in alloys-namely, cadmiumq2 copper, lead, bismuth,2 arsenic, and antimony-may be separated completely from quadrivalent tin by precipitation with hydrogen sulfide in solutions which contain a moderate concentration of hydrogen fluoride (about 1 per cent by weight). In his comprehensive scheme of qualitative analysis, Noyes3 made mention of the possible use of dilute hydrofluoric acid solutions of certain metals in quantitative analysis. McCay has proved that the separations from tin are quantitative in the cases of antimony,4 lead,5 ~ o p p e rand , ~ arsenica6 His experiments prove that the separations are successful only when antimony and arsenic are present quantitatively in the trivalent, and tin in the quadrivalent state. Iron and zinc, if present, will be found in the filtrate which contains the tin. Preliminary results indicate that under the
conditions recommended by McCay5 in liis scheme for the analysis of the tin-antimony alloys, no zinc is precipitated with the copper sulfide. This detail is being studied further. McCay has proposed a simple and accurate method for the analysis of the tin-antimony alloys, which is based upon his excellent method for the separation of antimony from tinS4s5The only criticism of the original method of which the author is aware was directed toward the necessity of using a platinum dish to remove the hydrogen fluoride before a determination of tin could be made. It was later shown by the author that the fluorine can be removed from the sphere of action by the addition of a large excess of boric acid to the solution. After the fluorine has thus been bound, perhaps in the little dissociated anion, BFI-, a complete precipitation of the tin as sulfide can be made in a glass vesseL7 Alternately, it was pointed out that the tin can be deposited electrolytically after the addition of oxalic acid.* The current efficiency was extremely
N
Received March 23, 1923. Thus far qualitative experiments only have been made in the instances of cadmium and bismuth. See Footnote 4 8 Tech. Quauterly, 16, 93 (1903); 17, 214 (1904) 4 J . A m . Chem. Soc , 31, 373 (1909). S I b z d . , 34, 1241 (1910). I b i d . , 4S, 1187 (1923). 1
2
’
Furman, J . A m . Chem. S O C ,40, 895 (1918). The details which are described in Classen-Hall, “Quantitative Analysis by Electrolysis,” 6th ed., 1913, p 135, John Wiley & Sons, Inc , were followed. 7
8
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low, however, and the process was so time-consuming as to be impractical. Recently, Kling and Lassieurg have recommended the McCay method for the separation of antimony from tin,* followed by the precipitation of the tin in the filtrate by means of cupferron, after the addition of a large excess of boric acid. In a subsequent communicationlo they state that the electrolytic precipitation of the tin is to be preferred to the precipitation by means of cupferron. They have found that a complete deposition of tin may be made in 20 minutes by using a current of 4 to 5 amperes and an apparatus suitable for rapid electro-analysis. (The electrode areas were not stated, nor were any experimental results given.) Their solutions differed from those which were previously employed by the author only in having present 2.5 grams tartaric acid, 5 to 10 grams sodium acetate, and 10 cc. concentrated hydrochloric acid, in addition to the quantities of other substances normally present. An extended series of quantitative experiments was made in which the conditions were as closely as possible those of Kling and Lassieur. Each solution contained 0.1 to 0.25 gram tin, 5 cc. 48 per cent hydrofluoric acid, 4 to 6 grams boric acid, 5 to 7 grams ammonium oxalate, 5 to 10 grams crystallized sodium acetate, and 5 to 10 cc. concentrated hydrochloric acid (specific gravity, 1.19). The tin was introduced in the form of stanni-ammonium chloride solution containing appropriate quantities of hydrochloric acid. The total volume was between 100 and 200 cc. A current strength of 4 to 5 amperes per 100 sq. cm. cathode surface a t 4 to 6 volts was employed; the speed of anode rotation was 600 to 800 per minute. I n no case was the tin completely deposited in one hour. The quantities not precipitated varied from 1 to 3 mg. A further electrolysis of 1 to 2 hours under the same conditions was necessary to complete the deposition. The small quantities of tin which were not precipitated in the first hour were always recovered upon continued electrolysis with cathodes freshly plated with copper; much less than 1 mg. of tin could be easily seen under these conditions. With stationary electrodes, employing a current of 0.5 ampere per 100 sq. cm. cathode a t 3 to 4 volts, other conditions as described above, complete deposition of the tin required 20 to 24 hours. I n the original experiments,’ which were made with sulfate solutions and without sodium acetate, the time required with stationary electrodes was 40 to 48 hours, other conditions being as here described. The acceleration of the deposition is undoubtedly due to the presence of both acetates and chlorides.ll Even with these additions, the method leaves much to be desired. Kling and Lassieur state that the cupferron precipitation of tin is most satisfactory from the standpoint of rapidity, ease of washing, and ignition of the tin to constant weight as oxide. Inasmuch as only three test analyses were given in the two papers cited, it seemed desirable to investigate the method further, especially since these results were obtained after precipitation of the antimony from a “hydrochloric acid solution of the two metals oxidized by potassium chlorate.” Such a procedure makes the separation of the antimony from tin absolutely unreliab1e.l2 Numerous qualitative experiments have shown conclusively that dilute hydrofluoric acid solutions of antimonic Comfit. r e n d , 170, 1112 (1920). Ibid., 173, 1081 (1921) 11 Engels, Bet‘., 28, 3187 (1895). 12 H. H. Willard has pointed out (private communication) that the accuracy of the tin results would not be affected since quinquivalent antimony is not precipitated by cupferron. This suggestion was studied experimentally and found to be correct. Kling and Lassieur give results which are correct for both antimony and tin. 9
10
Vol. 15, No. 10
compounds are very sluggishly, or not a t all, affected by a rapid stream of hydrogen sulfide in one hour.13 A new series of experiments was made in which Kling and Lassieur’s directions were carefully followed. Mixtures of 0.1 to 0.3 gram each of pure tin and antimony were dissolved by 10 cc. concentrated hydrochloric acid with gradual addition of 1 to 1.5 grams of potassium chlorate. In a second series dilute hydrochloric acid (specific gravity, 1 .lo) was used. These solutions were neutralized with sodium hydroxide, 5 grams tartaric acid were added, and the solutions, after warming until clear and cooling, were transferred to paraffin beakers. Ten grams crystallized sodium acetate and 10 cc. 48 per cent hydrofluoric acid were added. After ,dilution to 300 cc. and standing for one-half hour, each solution was treated with a rapid stream of hydrogen sulfide for one hour. The amounts of antimony thus precipitated ranged from 0.6 to 54 per cent of the quantities known to be present. Presumably, these figures represent the portion of the antimony which was not oxidized by the potassium chlorate. Abundant evidence of the presence of antimony in the filtrate was always obtained upon adding an excess of boric acid, warming the solution in a glass vessel, and again saturating it with hydrogen sulfide. The presence of a large amount of antimony sulfide admixed with the tin sulfide thus precipitated was confirmed by careful qualitative work. A similar erroneous idea of the conditions which are necessary for the separation of antimony from tin by the McCay method is to be found in the work of Ibbotson and Aitcheson.‘4 It cannot be too strongly emphasized that the antimony must be in the lower state of oxidation in order that this separation shall be complete.
EXPERIMENTAL A solution of stannic tin was prepared by dissolving about 4 grams of pure tin (the tin was of known high degree of purity, having been tested in connection with previous investigations of this series4r5)in 40 cc. of hot concentrated sulfuric acid. The solution was diluted to a liter after the addition of enough hydrochloric acid to prevent hydrolysis. Known portions of this solution were taken for analysis. Volumes recorded are a t 20” C. The tin was precipitated as metastannic acid and weighed as oxide, following the method of Rose.’S The following values were obtained : Solution Taken cc. 25 50 25 25 Average 25
Tin Found Gram 0,1032 0,2062 0.1034 0.1041 0.1034
PRECIPITATION OF TIN BY MEANS OF CUPFERRONNumerous analytical uses of cupferron (nitrosophenylhydroxylamineammonium) have been proposed since this reagent was first introduced by Baudisch.lG A compreThe author has made many qualitative experiments, dissolving 0 . j antimoniate in hydrofluoric acid (5 to 10 c c ) . Upon dilution t o 250 to 360 cc and passage of hydrogen sulfide for one hour, a slight yellow coloration sometimes appears after the first half hour, Upon standing, the solution generally becomes clear in a few hours. With a deficiency of acid, however, more or less rapid precipitation of antimony may occur. 11 “The Analysis of Non-Ferrous Alloys,” 2nd ed., 1922, p 132, Longmans, Green & Co., has the following erroneous statement: “For this separation (i. e., antimony from tin) the metals should exist in the higher state of oxidation in hydrochloric acid solution.*** The solution ***is treated with an excess of tartaric acid and then neutralized with sodium hydrate. A solution of 48 per cent hydrofluoric acid is then added, and this is followed by an excess of sodium acetate. After diluting largely ***the antimony is precipitated by a current of sulfuretted hydrogen,” etc. N o more unsuitable conditions could well have been chosen! 16 Pogg. Ann., 102, 164 (1861). 16 Chcm. Zlg., 33, 1298 (1909). la
to 1.0 gram of pure potassium
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October, 1923
hensive review of these uses has recently been made by Lundell and K n ~ w l e s . ~ 'Marvel and Kamm18 have studied and improved the methods of preparing cupferron. Presumably, the tin precipitate with cupferron is essentially Sn(Ca:,NzO&. Auger'g states that he has commenced a study of the complex salts of cupferron with molybdenum, tin, and cerium; hence no attempt was made to establish the composition of the precipitate. Known portions of the tin solution were taken. I n a number of cases the conditions were as nearly as possible those which would be encountered in the analysis of a copperlead-tin-antimony alloy by the McCay method-namely, 0.1 to 0.3 gram tin, 5 cc. 48 per cent hydrofluoric acid, 4 grams boric acid, 2 to 5 cc. concentrated sulfuric acid, and 5 to 10 cc. concentrated hydrochloric acid in a total volume of 200 Lo 500 cc. The cupferron was added in the form of a 10 per cent solution. The solution was filtered before using. Such a solution is stable for several weeks.20 Upon the addition of the reagent the tin precipitate separates in a white form, which is possibly an emulsion; it rapidly assumes a curdy appearance. Upon vigorous stirring in the presence of an excess of cupferron the precipitate generally passes through a stage in which it resembles superficially plastic sulfur. Finally, it becomes compact and brittle, and may be crushed to a powder with a glass rod.21 The whole series of transformations usually requires 30 to 45 minutes. Kling and Lassieur commence the filtration when the curdy state has been reached. In this study excellent results were obtained with the brittle precipitate, the filtration being very rapid. The precipitate ordinarily has a yellowish appearance when it has bocome brittle and compact. There is a very noticeable clearing up of the solution when precipitation is complete. A liberal excess of cupferron is desirable. The precipitate was washed with cold water. Precipitation and washing may easily be completed in less than an hour. After drying in a weighed crucible, the organic matter was expelled by gentle ignition. The stannic oxide was brought to constant weight in the usual manner. If the quantity of tin is larger than 0.1 to 0.3 gram, it becomes increasingly difficult to remove carbon. By breaking up the precipitate after the first ignition a rapid removal of carbon is effected. Solutions of hydrofluoric acid to which an excess of boric acid has been added have only a slight solvent action upon glass, even on boiling. Nevertheless, those precipitates which were obtained from such solutions were tested for the presence of silica. A portion of the ignited stannic oxide was transferred to a platinum crucible and brought to constant weight. A fewdrops of water and dilute nitric acid, and 5 cc. 48 per cent hydrofluoric acid were added. Upon evaporation and ignition no change in weight occurred. TABLEI- DETERMINATION O F TIN AFTER PRECIPITATION Expt. i
:i :i
; ti I
Tin Taken Gram
0.1083 o ,2068 0.1034 0.1216 0.2138 0.2068 0.1034
CUPFERRON Tin Found Gram
0.1087 0.2066 0.1032 0.1221 0.2142 0.2062 0.1036
Error Mg.
0.4 -0.2 -0.2 0.5 0.4 -0.6
0.2
BY
18
SEPARATION OF TIK FROM ZINC-Z~C and iron, when originally present in a tin alloy, will be found in the filtrate which contains tin in the course of the analysis by the methods mentioned.6 Cupferron will of course precipitate the iron with the tin. The amounts of iron in tin alloys are generally small. It seems obvious that the iron oxide could be extracted from the ignited precipitate and its amount determined by a suitable method. Experiments prove that a very satisfactory separation of tin from zinc is effected by precipitation with cupferron. A solution of pure zinc sulfate was prepared and standardized, the zinc being weighed as pyrophosphate. Zinc Solution Taken cc
Zinc Found Gram
25 50 25
0.1484 0,2948 0.1481 0,2958 0.1479
.
50
Average
25
Known portions of the zinc and tin solutions were mixed. The tin was precipitated by means of cupferron, and weighed as oxide. The determination of zinc in the filtrates was a matter of considerable difficulty. The method cannot be recommended when a rapid determination of the zinc is essential. Zinc was weighed as the pyrophosphate, either after repeated precipitations as the double ammonium phosphate, with intervening filtrations to remove organic matter, or after previous precipitation as the sulfide. TABLE11-SEPARATION Tin Taken ExDt. Gram 1 - 0.1034
2 3 4 5
6 7
0.2068 0,1448 0.1034 0,1034 0,2068 0.1034
TIN
Tin Found Gram
Error Ma.
ZINC BY MEANS OF CUPBERRON Zinc Taken Zinc Found Error Gram Gram ME.
0.1037 0,2069 0,1444 0.1040 0.1032 0,2073 0.1037
0.3 0.1 -0.4 0.6 -0.2 0.5 0.3
0,1479 0,1491 0,1479 0.1489 0,2958 0,2953 0.1479 Not determined 0.2958 N o t determined 0.1479 0.1484 0.2958 0.2956
OB
FROM
~
1.2 1.0 -0.5
.. ..
0.5 -0.2
In Experiments 2 and 6 no hydrofluoric acid was present.. In these cases the filtrate was evaporated with nitric acid in order to destroy organic matter. The nitric acid was then expelled a t the temperature of boiling sulfuric acid. The general conditions were similar to tkiose of the experiments recorded in Table I. SEPARATION O F TIN FROM MSNGANESE, ZINC, COBALT, AND NICKEL-It seemed obvious that cupferron would separate tin from any or all of these met'als. Solutions were prepared which contained known amounts of tin and from 0.1 to 0.15 gram each of manganese, nickel, cobalt, and zinc. Only the tin was determined. Tin Taken Gram
0,1034 0,2068
Tin Found Gram
0.1035 0.2073
MEANS O F
Total Volume
cc. 300 170 170 400 400 500 250
In the first three experiments no hydrofluoric acid was present. 17
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THIS JOURNAL,12, 344 (1920). J . Ant. Chem. SOG.,41, 276 (1919). A bibliography of the uses of
cupferron is given. 1 9 Compl. rend., 110, 995 (1920). 20 See references cited by Lundell and Knowles, loc. c i l . 2 1 Fresenius, 2. anal. Chem., 60, 37 (1911),describes a similar series of transformations of the iron salt of cupferron.
Greetings Exchanged While the Leather Division was in session at Milwaukee, delegates from other parts of the world were already proceeding t o Barcelona, Spain, t o attend the international meeting of the Society of Leather Trades Chemists. I n view of the unity of purpose of the two organizations, the Leather Division authorized the sending of the following message b y cable: SOCIETY OF LEATHERTRADES CHEMISTS, CALLE URGUL 187, BARCELONA, SPAIN: T h e Leather Division of t h e American Chemical Society in congress assembled a t Milwaukee sends greetings and best wishes for a successful meeting. (.%gned) JOHN ARTHURWILSON, Chairman.
Later the following reply was received by cable: T h e Society of Leather Trades Chemists in conference thanks the Leather Division of the American Chemical Society for its greetings a n d good wishes which are heartily reciprocated. (Signed) E. SCHELL,President.
