IMPROVED METHODS FOR SUBDIVIDING CATION GROUP I1 AND FOR SEPARATING ANTIMONIOUS AND STANNIC SULFIDES A. R. MIDDLETON Purdue University, Lafaptte, Indiana AND
G. T. WERNIMONT The Eastman Kodak Company, Rochester, New York
In his recently issued "Brief Course," page 166, Curtman1 uses NaOH to separate the sulfides. We had already observed the solubility of Hg(HS), in NaOH and used the latter for the subdivision of Group I1 cations. We convinced ourselves that a decided increase of accuracy and saving of time result. When dealing with the rather large amounts provided for in Curtman we have found it advantageous to transfer the group precipitate to a mortar, add 3 ml. of 6 N NaOH and 2 ml. of NaOH saturated with H B and to slime thoroughly with a pestle for ten minutes. The 5 ml. of water saturated with HzS should be added just before filtering. Sliming is advantageous also when
separating mercuric and arsenious sulfides by 15N NH3. When working with semi-micro amounts, 3-10 mg. of well-washed group precipitate should be treated with three drops of 6 N NaOH and three drops of 6 N NaOH saturated with H2S and the mixture warmed and stirred five minutes with a platinum wire. After centrifuging and removing the liquid the treatment should be repeated with the same amounts of reagents and stirring for five minutes. Experience with large classes has shown that this effects complete solution of HgS. The entire operation is carried out in the centrifuge tube. J. Kunz' has shown that H2S effects a clean separation of SbS3and SnSa if the solution a t the currect CHI is saturated with NaCl. The solubility products of the two sulfides differ too little for sharp separation solely by control of CA+. However, a large Ccj- by stabilizing SnCla= makes possible a satisfactory separation. Since a t no point in the separation of the IIB elements is a considerable amount of sulfur formed when NaOH and NaCl are used, mercury, arsenic, antimony, and stannic tin can be identified by the characteristic colors of their sulfides and no confirmatory tests are necessary. We can strongly recommend these reagents.
' CURTMAN,L. J., "A brief c o m e in qualitative chemical analysis," The Macmillan Company, New York City, 1936.
Kmz, J., "Methoden der qualitstiven Analyse der Schwefelwassersto5gruppe," Hclu. Chim. A&. 16,1044 (1933).
USE OF alkali polysulfides to separate the two divisions of cation group I1 is unnecessary, provided tin be in the qnadrivalent state, as it usually is in actual practice. Even freshly precipitated mercuric sulfide is readily soluble in NaOH. If it is washed long enough it becomes insoluble. This seems to be additional evidence that it, and presumably the other "sulfides" of the group, are really hydrosulfides when first preapitated. Hg(SH*)
+ 20H- F? HgSs- + 2H20
