1904.] McCAY — trisulphoxyarse:nic acid. 115 



If a dilute solution of sodium trisulphoxyarseniate be treated with 

 enough acid to render it strongly acid, then shaken violently and 

 filtered, the filtrate is clear and becomes but faintly turbid on 

 boiling. If a dilute solution of sodium disulphoxyarseniate of the 

 same concentration be tested in a similar way, the filtrate becomes 

 strongly turbid on boiling. When these tests are made in flasks 

 and the flasks, immediately after the addition of the hydrochloric 

 acid, are stoppered, so as to prevent the escape of the sulphuretted 

 hydrogen, at the end of thirty-six hours no smell of the gas can be 

 detected in the flask which contained the disulphoxy-salt, while it 

 is still very pronounced in the one which contained the trisulphoxy- 

 compound. These two reactions have been studied very carefully. 

 It appears that the trisulphoxy-acid breaks down as follows : 



the disulphoxy-compound thus : 



4S 



The three sulphoxyarsenic acids are not precipitated at once by 

 Weinland's^ reagent, which fact serves to distinguish them from 

 sulpharsenic acid. All three can be readily separated from arsenic 

 acid by means of magnesia mixture which precipitates only the 

 latter. The formation of these three sulphoxyarsenic acids, their 

 instability and the products of their decomposition, account in a 

 perfectly rational manner for all the irregularities accompanying the 

 interaction of sulphuretted hydrogen and arsenic acid. This is a 

 summary of our work so far as it has thus far progressed. 



Princeton^ JV. /., April 4, 1^04. 



^ An aqueous solution of tartar emetic and Rochelle salt. 



