OF ARTS AND SCIENCES. 59 



Analytical Methods. — Arsenic is most conveniently determined in 

 these salts by reduction with sulphurous acid and precipitation of 

 arsenious sulphide by sulphydric acid. The sulphide is then to be 

 weighed upon an asbestos filter. In the filtrate which contains the 

 vanadium as dioxide the vanadic pentoxide may be determined by 

 potassic hypermanganate. Dilute sulphuric acid is to be added in 

 place of chlorhydric acid before precipitation with sulphydric acid. 

 Water cannot be accurately determined in these salts by ignition with 

 sodic tungstate, as a greater or less quantity of arsenic oxide is always 

 volatilized. The best method consists in cautiously heating the salt 

 over a radiating cup of sheet-iron until a constant weight is obtained. 



5 : 8 Arsenio-vanadic Acid. — When sodic divanadate and arsenate 

 are dissolved together in boiling water, and nitric acid is added in small 

 portions at a time, a deep orange liquid is obtained which on evaporation 

 to dryness upon a water-bath yields an orange-yellow crystalline mass. 

 This is to be purified by careful washing with cold water, when a 

 beautiful crystalline orange-colored salt remains. The salt is some- 

 what soluble in cold, and readily in hot water. The solution is very 

 easily reduced by dust or other organic matters, and becomes greenish- 

 orange with formation of a greater or less quantity of an ai'senio- 

 vanadico-vanadate. It is then difficult to reoxidize the solution so as 

 to obtain the original compound. On analysis, 



( 0.8558 gr. gave 0.3374 gr. As.S, = SG.ST^As.p. 



X 0.8558 gr. " 0.4058 gr. V._,6, with KMnO, = 47.41 % 

 0.8715 gr. lost over a radiator 0.1358 gr. = 15.58% 



The analyses correspond to the formula 



5 AsgOj . 8 V2O5 . 3 H.O -f 24 aq, 

 which requires : 



Calc'd. Found. 



47.18) 3^3^ 47.41) g^^S 



37.13) 36.87) 



15.69 15.58 



3097 100.00 99.86 



The water, as estimated by difference, amounts to 15.72, so that the 

 direct determination is nearly correct, and no fixed base is present. In 

 a second preparation, in which I employed residues containing arsenic 

 and vanadium from the preparation of the arsenio-vanadico-vanadates 



