On the Sulphates of Alumina and of Chromium. 281 



obstinacy. The sulphocyanuret may be obtained by using 

 very concentrated solutions of the sulphate of copper and the 

 sulphocyanuret of potassium ; it is precipitated as a black pow- 

 der, and is anhydrous. Its decomposition with water, which 

 has been studied by Claus, is very curious ; it changes in water 

 into the white disulphocyanuret ; it appears that at the same 

 time hydrosulphocyanic, hydrocyanic and sulphuric acids are 

 formed (the iron salt appears to be similar in properties). The 

 sulphocyanuret of copper forms a crystallizable salt with, one 

 atom of ammonia. — (PoggendorfPs Annale?i, vol. xlvi. p. 63.) 



On the Sulphates of Alumina and of Chromium. 



In the 45th volume of PoggendorfPs Annals, page 99, 

 Hertwig published apaper on the proportions in which alumino- 

 sulphate of potassa (alum) can combine with water; he found 

 that when large crystals of common alum are allowed to lie 

 for some time in concentrated sulphuric acid they are not 

 dissolved but dispersed through the acid, forming a gelatinous 

 mass; water throws down a crystalline powder, which on being 

 pressed between bibulous paper and recrystallized from a hot 

 solution, gives a salt in the form of regular octohedrons, which 

 contains only 14 atoms of water, whereas the common alum 

 contains 24. In the same volume, page 331, there is a paper 

 by Heintz who has not been able by these means to procure 



anything but common alum (Al S 3 , K S + 24 aq). By the 

 united action of heat and sulphuric acid Hertwig obtained an- 

 other compound, Al S 3 + K S ■+• 3 aq, which is a very insoluble 

 salt, and becomes still more so when strongly heated; it must 

 therefore be an isomeric modification of anhydrous alum. 

 Common alum when kept for a length of time at a tempera- 

 ture of 100° C. loses 10 atoms of water, but this salt differs 

 considerably in its properties from that with 14 atoms of 

 water mentioned above. By a heat of 120° to 160° a com- 

 pound of 5 atoms is obtained, at 200° with 1 atom. By 

 somewhat similar means to those employed by Hertwig, Heintz 



has obtained two salts with oxide of iron, Fe S 3 , K S + 3 aq 



and Fe S 3 , K S + 2 aq. The true colour of the iron alum 



appears to be violet, when mixed with common alum it is 

 quite white. In vol. lvi. of the same Journal, p. 95, Hertwig 

 has described some modifications of the chrome alum. If a 

 very concentrated solution of the green double sulphate be 

 evaporated with concentrated sulphuric acid as long as water 

 is driven off, a green anhydrous chromosulphate of potassa is 



