upon Fcrrocyanide of Potassium. 23 



gave of oxide of iron 5*9 grs. ; the solution by precipitation 

 with baryta afforded 34 - 2 grs. of sulphate = 1 1*74? grs. of sul- 

 phuric acid. 



100 parts will therefore contain, if the ammonia be taken 

 by difference, — 



Sulphuric acid . . . 590 58*7 



Peroxide of iron . . . 30-0 29*5 



Potash 7*9 



Oxide of ammonium . 3*1 



100-0 



A separate specimen, the result of another operation, gave 

 numbers closely coinciding with the above. 



It will be seen that the relation of the sulphuric acid to the 

 oxide of iron is almost exactly that which exists in common 

 iron-alum ; the formula 



2 (Fe 3 3>S S0 3 ) +N K0 6 S O d3 



gives, reckoned to 100 parts, — 



Sulphuric acid .... 58*0 

 Peroxide of iron . . . 28*8 



Potash 8*5 



Oxide of ammonium . . 4*7 



lOO'O 



Taking into account the impossibility of completely wash- 

 ing the crystals without causing decomposition, a comparison 

 of the calculated and found results will perhaps be deemed 

 satisfactory. 



This anhydrous iron-alum is apparently the type of a num- 

 ber of crystalline anhydrous sulphates which may be formed 

 under similar circumstances. For example, when green vitriol 

 in powder is boiled with strong sulphuric acid it is dissolved, 

 sulphurous acid is disengaged, the protoxide of iron passing 

 to peroxide, which, as fast as it is formed, falls down in com- 

 bination with the acid as a crystalline pinkish-white powder. 

 Anhydrous sulphates of copper and nickel may be obtained 

 by a similar process ; also the double sulphate of nickel and 

 potash. The copper salt has a beautiful lilac colour ; that of 

 nickel is bright yellow. All these compounds are, however, 

 changed by contact with water; the persulphate of iron is the 

 most stable, but even that ends by dissolving in great part. 



There is no difficulty in explaining the decomposition un- 

 dergone by the ferrocyanide of potassium under the influence 

 of the acid, and its conversion into the products observed. 



1 equivalent of ferrocyanide of potassium and 9 equivalents 

 of water contain the elements of 6 equivalents of carbonic 



