CONTAINING POTASH. 431 



4. Potash-protosulphate of iron. This salt 



1 A protosul- 



was obtained by mixing solutions of protosul- phate of 

 phate of iron, and sulphate of potash in the 

 atomic proportions, and concentrating the solu- 

 tion beautiful crystals of the compound salt 

 were deposited, They had a very light green 

 colour, and were much harder and firmer than 

 the protosulphate of iron, were more opaque, 

 and not liable to undergo any alteration from 

 exposure to the air. The crystals were so ir- 

 regular that it was difficult to make out the 

 shape ; at first view they had a lenticular ap- 

 pearance, but when closely examined, faces 

 appeared which corresponded with those of an 

 octahedron, apparently low, and somewhat 

 broader on two sides than on the other two. 

 The taste of this salt was similar to that of pro- 

 tosulphate of iron ; but it was less soluble in 

 water, and the solution, which was almost co- 

 lourless, had a tendency especially when heated 

 to deposite flocks of peroxide of iron. This salt 

 was analyzed in the following way : 



26*125 grains of the crystals were exposed on 

 a glass capsule to the heat of a spirit lamp, cau- 

 tiously applied till they ceased to give out mois- 

 ture. By this treatment they became opaque, 

 and of a dull white colour, and the loss of weight 

 was 5'878 grains. The residual salt was dis- 

 solved in water, and the liquid mixed with a 

 solution of 2(r.5 grains of chloride of barium. 



