114 MCCAY— TRISULPHOXYARSENIC ACID. [April 1, 



tertiary sodium salt of the acid commences to separate out in 

 feathery crystals which, in the course of twelve hours, pass over 

 into fine fern-like forms. The compound is purified by recrystalli- 

 zation. The yields are very satisfactory. Thirty grams of AS2S5 

 yield about thirty grams of the impure salt. 



The compound possesses a composition represented by the 



formula 



Na^AsOSg-f iiHoO. 



Calculated. Found. 



Na 15.22% ^5-65% 



' As 16.50" ■ 16.84" 



O ••• 3-52" 3-45" 



g" 21.16*' 20.74" 



HO.. 43.60" 43-32 " 



100.00 100.00 



The tertiary potassium salt is prepared in an analogous manner. 

 On the addition of the alcohol it separates out in the form of a 

 light yellow oil, which, however, solidifies to a straw-colored, 

 cr'^ystalline mass when kept for some hours at —20" C. 

 It crystallizes with seven molecules of water : 



K3ASOS3 4- 7H2O. 



By adding an alcoholic solution of strontium chloride to an 

 aqueous solution of the sodium salt, the double trisulphoxyarseniate 

 of sodium and strontium is precipitated in a crystalline condition : 



NaSrAsOSg + loH.O. 



Barium chloride produces in a solution of the tertiary potassium 

 salt a crystalline precipitate of potassium barium trisulphoxy- 

 arseniate : KBaAsOS3 + 7H,0. 



Aqueous solutions of sodium trisulphoxyarseniate are not precipi- 

 tated by strontium chloride. This reaction has been made use of 

 for separating the small amount of monosulphoxy-salt which is 

 occasionally thrown down along with the trisulphoxy-compound. 

 Barium chloride precipitates both the di- and trisulphoxyarsemc 

 acids but the barium salt of the latter acid is more soluble than 

 that of the former. The behavior of these two acids toward 

 hydrochloric acid is also a means of distinguishing between them. 



