1835.] Improvements in Science. 195 



exposure to the air is converted into the peroxide salt. The 

 latter is a black flocky precipitate, soluble in caustic am- 

 monia, and giving a dark colour to the solution. After 

 evaporation to dryness, a dark extract looking mass remains, 

 from which water dissolves a neutral double salt, and leaves 

 a basic oxide salt. Caustic potash likewise dissolves the 

 perapocrenate of iron, but a precipitate soon subsides, the 

 apocrenate of potash being dissolved in the solution, and a 

 basic salt separating. The solution may be freed completely 

 from iron, by passing a current of sulphuretted hydrogen 

 through it, but in no other way can the iron be entirely 

 precipitated. 



Croconate of Potash may be formed by passing carbonic 

 oxide through a glass tube over fused potassium. When 

 exposed to the air the compound inflames with explosion, 

 and dissolving in water, and affording, by evaporation, long 

 prismatic needles of croconate of potash. It consists of 



Carbon . . . 27-83 

 Oxygen ... 29-17 

 Potash . . . 43-00 



100-00 

 Vermilion. — According to Wehrle, vermilion similar to 

 that of China can be made by the following process : — Sublime 

 common vermilion, in very fine powder, with the hundredth 

 of its weight of sulphuret of antimony, then digest the subli- 

 mate with the sulphuret of potassium, and afterwards with 

 muriatic acid, and lastly, with J per cent, of gelatine, dis- 

 solved in water ; wash and dry it ; a very small portion of 

 sulphuret of antimony is sufficient to impart to the vermilion 

 a beautiful crimson colour. (Poggendorff, Ann. xxvii.) 



Potash Cyanide of Iridium. — This salt, which crystallizes 

 in long four-sided prisms, resembling gypsum, was obtained 

 by Mr. Booth of Philadelphia, by heating a mixture of 

 anhydrous potash cyanide of iron with powder of iridium. 

 The salt is colourless, soluble in water, insoluble in alcohol, 

 is not precipitated by muriatic acid, and contains no water. 

 By heating it becomes black, and, if the heat is pushed 

 farther the iridium separates. 



o2 



