1818.] Triple Prussiate of Potash 217 



the information of your chemical readers, that I have discovered 

 a method of obtaining the ferraretted chyazic acid in the state 

 of crystals. The process is as follows : 



Dissolve 58 grs. of crystallized tartaric acid in spirit of wine, 

 and pour the solution into a phial containing 50 grs. of ferruretted 

 chyazate of potash dissolved in two or three drams of warm 

 water ; by this process the whole of the tartaric acid will combine 

 with, and precipitate the potash in, the state of super-tartrate of 

 potash, and the alcoholic fluid will contain nothing but ferru- 

 retted chyazic acid, which may be obtained from it in small 

 crystals, generally resembling a cube, by spontaneous evapo- 

 ration. 



P. S. Since writing the above, I have made the experiment 

 of decomposing ferruretted chyazate of potash by ignited 

 peroxide of copper ; I used one gr. of the salt with 35 grs. of the 

 oxide ; the products were, at mean temperature and pressure, 



Cubic Inches. 



Carbonic acid 1*39 



Azote 0-37 



V76 



The calculated products on the view which I took in my last 

 letter are, 



Cubic Inches. 



Carbonic acid T42 



Azote 0-36 



1-78 



The experiment, therefore, completely confirms the explana 

 tion which I then proposed. 



Dr. Thomson employed too little peroxide of copper; and 

 this, I believe, is the principal cause why his results differ from 

 the above. I am, Gentlemen, 



Your most obedient servant, 



R. PORRETT, Jun. 



Article XII. 



Some Account of Prof. Smith's Collection of Plants formed in the 

 Neighbourhood of the River Zaire. Abridged from an Essay 

 by Mr. Brown, published in Capt. Tuckey's Narrative. 



Mr. Brown arranges his observations under three heads; 

 in the first place he proposes to state what relates to the three 



