Gooch and Phelps — Reduction of Arsenic Acid. 217 



the simultaneous reconversion of the arsenic to the higher form 

 of oxidation. In such a solution, especially if it is not very hot, 

 hydrogen sulphide precipitates the arsenic only slowly, but the 

 addition of a little stannous chloride dissolved in hydrochloric 

 acid of half-strength to the hot solution reduces the arsenic to 

 the lower form of oxidation and prepares the way for the im- 

 mediate precipitation of arsenious sulphide by hydrogen sul- 

 phide. Antimonic acid is likewise reduced under the condi- 

 tions of the distillation ; but, as Koehler has shown,* neither 

 small amounts of antimony and tin, which if present originally 

 may pass partially to the distillate, nor the tin added to effect 

 the reduction of the arsenic finally, will be precipitated by 

 hydrogen sulphide under the existing conditions of tempera- 

 ture and acidity. 



The results of experiment are recorded in the accompanying 

 table. 



(i) 



(2) 



(3) 



(4) 



(5) 



(6) 



CO 



(3) 



(9) 



(10) 



(11) 

 (12) 



(13) 



(14) 

 (15) 



(16) 



Arsenic 



taken as 



H 3 As0 4 



grm. 



0-0001 



o-ooio 

 o-oioo 

 o-iooo 



0:4000 

 1-0000 



0-0001 



o-oooi 



00010 



o-oioo 



o-ooo I 

 o-oooi 



Antimony- 

 taken as 

 H s Sb0 4 

 arm. 



0-4000 

 0-4000 



0-0001 



o-oooi 



0-0001 



Tin 



taken as 



SnCl 4 



grm. 



0-4000 

 0-4000 



o-oooi 



Precipitation by 



H 2 S m successive 



distillates niter 



treatment with 



SnClo 



I None 



I-X None 

 j I Found 

 I II No D e 

 J I Found 

 I II None 

 j I-II Found 

 j III None 

 \ I-III Found 

 } IV None 

 | I-VI Found 

 } VII None 

 j I-X Found 

 i XI None 



I None 

 \ I-II Found 

 / III None 

 j I Found 

 } II None 

 j I Found 

 / II None 

 ] I-II Found 

 I III None 



I None 

 j I-II Found 

 I III Xone 

 j I Found 

 I II None 



Precipitation by 

 H 2 S in the re- 

 sidue dissolved 



in water. 

 None 

 Faint coloration 



None 

 None 

 None 



Faiut coloration 



Orange 



precipitationf 

 Orange 



precipitationf 

 Large 



Large 



Distinct color 



Distinct color 



Distinct orange 



Large 



Large 



Distinct color 



*Zeit. fur Anal. Chem., xxix, 192. 



t Subsequently identified as antimony sulphide by depositing the metal on 

 platinum. 



