214 Mr. Porrett on the [Sept. 



Article XI. 



On the Triple Prussiate of Potash. By R. Porrett, Esq. 

 (To the Editors of the Annals of Philosophy.) 



GENTLEMEN, Tower, August 13, 1818. 



I was much gratified on reading in your last number a very 

 curious and instructive paper by Dr. Thomson, containing his 

 analysis of the salt usually (but very erroneously) termed triple 

 prussiate of potash ; and having compared this analysis with 

 mine, published in the Philosophical Transactions for 1814, the 

 differences between them appeared as follow : 



By my Analysis. By Dr. Thomson's. 



Water 13-00 13-00 



Ferruginous acid . . . 47-66 45*90 



Potash 39-34 41-64 



On observing these differences, my first opinion was that Dr. 

 Thomson's analysis was the most correct ; but when I perceived 

 that his results did not accord with the atomic theory, 1 must 

 confess that my faith in them was shaken. In order to remove 

 or confirm my doubts, I had recourse to experiment. 



I took 50 grs. of ferruretted chyazate of potash, and having 

 dissolved them in about two drams of warm water, I added to 

 the solution 70 grs. of crystallized tartaric acid, previously dis- 

 solved in about four drams of warm water ; the mixed liquid, 

 after having been left for a day, was poured off from the super- 

 tartrate of potash which it had deposited. I washed the salt thus 

 obtained with small portions of spirit of wine several times, and 

 added these washings to the decanted fluid ; this fluid after- 

 wards deposited a minute quantity more of the super-tartrate, 

 which I added to what I had before procured. After satisfying 

 myself that the fluid contained no more super-tartrate, I dried 

 what I had obtained at a steam heat; it then weighed 72*35 grs. 



From Berzelius's analysis of super-tartrate of potash, it 

 appears that 100 parts contain 24-8 of potash; therefore, these 

 72*35 grs. must contain 17-9 grs. of that alkali. 



Thus it appears that 50 grs. of ferruretted chyazate of potash 

 contain 17*9 grs. of potash; consequently 100 grs. must contain 

 35' 8 : then as Dr. Thomson agrees with me as to the quantity of 

 water of crystallization being 13 grs. it follows that the quantity 

 of ferruginous acid must be 51*2 grs. and that the weight of an 

 atom of this acid must be 85*9, the weight of an atom of 

 potash being 59*1. 



By a repetition of my analysis of ferruretted chyazate of 

 barytes, I find that I had made a considerable mistake in the 

 quantity of water which it contains ; its composition, instead of 



