1819.] some new Combinations of Prussic Acid. 447 



phuric acid disengaged a great deal of carbonic acid, and formed 

 a sulphate without destroying the blue colour. 



XVI. Prussiate of Sulphate of Lime. 



Sulphate of lime appears to me one of the substances which 

 has the greatest affinity for prussic acid of those which I tried. 

 I precipitated muriate of lime by sulphuric acid diluted with 

 seven or eight times its weight of water. I heated it to the 

 boiling temperature, and added prussiate of potash. There wa8 

 immediately formed a prussiate of a fine green, which passed 

 very speedily to blue. 



Calcined sulphate, or fine plaster of Paris, may be employed 

 to form this prussiate. It is diffused through a great quantity of 

 water, and then a solution of prussiate of potash having an excess 

 of muriatic acid previously added to it, is poured in. Boiling- 

 causes it to assume a green colour. 



When the prussiate of sulphate of lime has a strong blue 

 colour, and contains a sufficient quantity of prussic acid, it is 

 insoluble in water, and in the mineral acids : 15 gr. of prussiate 

 of potash were sufficient to give to 10U gr. of calcined plaster a 

 rery distinct blue colour. 



The sulphates of strontian and barytes newly precipitated and 

 treated like that of lime, likewise furnished deep blue prassiates. 



XVII. Prussiate made with common While Clay. 



The dry earths and the metallic oxides in powder, when thev 

 are sufficiently divided, combine very well with prussic acid, 

 when assisted by heat. 



1 mixed with water, fine white clay employed atSt.Petersburgh 

 for the manufacture of porcelain, and which does not contain an 

 atom of iron. I decanted off the finest parts, which I boiled 

 with prussiate of potash without producing any change in the 

 colour. The addition of muriatic acid made the mixture become 

 green. After a quarter of an hour's boiling, 1 poured the prus- 

 siate formed into a plate. It had a fine green colour, and 

 became blue after some days exposure to the air. 



This prussiate may become useful in the arts. It has the 

 advantage of being always of a distinct blue colour whatever be 

 the proportion of acid employed to form it. This is not the 

 case with iron, which gives yellow and green subprussiates. 



XVIII. Prjissiate formed with GreenisJi Grey Clay. 



This clay, which is found abundantly in the neighbourhood of 

 St. ^etersburgh, and which I conceive to be coloured with a 

 little chlorite, when treated like the white clay, gave also a beau- 

 tiful blue prussiate. As it contains iron, its prussiate is nearly 

 the same as common prussian blue. It requires longer boiling 

 than the preceding, because it is difficult to destroy the green 



