The Detection of Arsenic, Antimony and Tin. 



BY HAMILTON P. CADV, 



The detection of arsenic, antimony and tin in the presence of 

 one another is a rather long and tedious process when carried out 

 by the ordinary qualitative methods. The Marsh test, either in its 

 original form or with the silver nitrate modification, is probably the 

 best of the common methods, but even this is not very successful 

 in the hands of many students. The following method has been 

 found rapid and convenient: 



The process is carried out as follows: three or four e. e. of the 

 solution to be tested is placed in a test tube, and about one and 

 one-half times the volume of concentrated hydrochloric acid is then 

 added, and hydrogen sulfid passed through the solution. The 

 arsenic, whether in the arsenous or arsenic condition, is precipitated 

 as As, S3, while the antimony and tin remain in solution. If the 

 arsenic is in the arsenous condition, the precipitate will settle out, 

 leaving the solution clear; while if it is in the arsenic condition, 

 the sulfur formed during its reduction will remain suspended, ren- 

 dering the liquid turbid. So one can not only detect the arsenic, 

 but can also tell whether it is arsenous or arsenic. If arsenic acid 

 is formed it will, of course, be necessary to test for arsenous some 

 other way. 



After the arsenic has been precipitated the tube is inclined at an 

 angle of about thirty degrees, and cold water saturated witii 

 hydrogen sulfid is carefully poured in, stirring up the solution as 

 little as possible. Almost as soon as the first drops of water touch 

 the solution the antimony sulfid is precipitated as an orange red 

 ring or layer floating on the highly acid solution. Upon further 

 dilution the yellow stannic sulfid is precipitated and blending into 

 this the brown to black stannous sulfid. After standing a few mo- 

 ments there wdll be a marked line of demarkation between the 

 antimony and tin. A tube containing these substances, when 

 treated in this way, presents a very striking appearance with its 

 several highly colored layers. 



(ib9) KAX. IXIV. QrAR.. VOL. IX, XO. 4, OCT. 190(t, SERIES A. 



