OP ARTS AND SCIENCES. 7 



so that in fact it is difficult to distinguish between the two in any other 

 way than by the habitus of the crystals and by analysis. 



When the 10:4 salt is dissolved in water and a current of sulphydric 

 acid gas passed into the solution to the point of saturation, the liquid 

 becomes at first yellow, and finally orange red. On standing or evapo- 

 ration, it deposits browu tungstic sulphide, WS 3 , and the still faintly 

 yellow mother liquor gives fine colorless triclinic crystals, which are 

 separate and distinct, not twinned or aggregated in masses like the 10:4 

 salt. These crystals after recrystallization have the formula of the 

 12 :5 salt presently to be described, namely, 



12Wo 3 .5Na 2 + 28 aq, 



as the following analyses show : — 



The formation of the 12:5 from the 10 : 4 salt is easily explained, 

 as well as the separation of the tungstic sulphide, since we have 



2 (10 W0 8 . 4 Na 2 0) -f 5 H 2 S = 12 W0 3 . 5 Na 2 -f 3 W0 3 . Na 2 

 _[_ 5 WS, -f 5 H 2 0. 



A concentrated solution of the 10 : 4 sodium salt is resolved by boiling 

 into the 12:5 salt and other compounds difficult to isolate in a state of 

 purity. When a hot solution of potassic bromide or nitrate is added 

 to a boiling solution of the 10:4 sodium salt, a white crystalline precipi- 

 tate is speedily formed, which has the formula 



12 W0 8 . 5 K 2 + 10 aq. 



But if a cold solution of a potassic salt is added to a cold solution of 

 the 10:4 sodium salt, a white crystalline precipitate is formed, which has 

 the formula 



10WO 3 . 4K 2 + 9aq. 



