ELISHA MITCHELL SCIENTIFIC SOCIETY 80 
NOTE ON A QUALITATIVE TEST FOR TIN.' 
BY CHARLES BASKERVILLE. 
Scarcely any instructor in Qualitative Analysis has failed 
to have difficulty in having his students make a satisfactory 
separation of arsenic, antimony and tin. Hither of the ordi- 
nary methods of separation of the arsenic, namely, solution of 
arsenic sulphide in ammonium carbonate or the solution of 
the mixed sulphides of tin and antimony in hot concentrated 
hydrochloric acid, answer very wellforthe arsenic. The pres- 
ence of antimony in the hydrochloric acid solution is easily 
proven by its precipitation upon platinum in the presence of 
metallic zinc, subsequent solution in dilute nitric or tartaric 
acid, andsoon. ‘The difficulty isin proving the presence of 
tin. Unless most of the acid has been driven off and the so- 
lution well diluted the tin fails to be precipitated on the zinc. 
We have usually tested the solution directly with mercuric 
chloride and hydrogen sulphide for tin. These tests are not 
always satisfactory, more or less doubt existing in the stu- 
dent’s mind, especially if all the antimony has not been re- 
moved. 
Longstaff (Chem. News, S0, 282) suggests reversing the 
test given by Fresenius (Qual. Anal., 8th Edit.. p. 217, trans. 
by Johnson) for molybdic acid. Stannous chloride produces a 
blue coloration with molybdic acid. He uses ammonium mo- 
lybdate. 
We carry out the test as follows: filter from the diluted 
liquid any remaining particles of zinc and add a pinch of pow- 
dered molybdic acid. A deep blue color shows the presence 
of tin. We have proved the presence of one part in five thous- 
and with the very roughest conditions under which a most 
careless student may work. Longstaff states that with every 
precaution for exclusion of air it is delicate for one part 
ina million. The color disappears in the presence of con- 
centrated hydrochloric acid. 
The presence of arsenic, antimony and zinc compounds has 
1 Read at the Midwinter Meeting of the North Carolina Section of 
the American Chemical Society February 24th, 1900. 
