I N D U S T R I A L A,VD E S G I S E E R I S G CHEJIISTRY
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
1073
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.
