5$8 Mr. PoRRETT on the nature of the Salts 
Ferruretted chyazic acid 53»38o 
Per-oxide of iron - S4 235 
Water - - - 12.385 
100.000 
Before I dismiss the subject of the ferruretted chyazates, I 
beg to make some remarks on the opinion generally enter- 
tained by the most eminent chemists, of the inadequacy of 
these salts as tests for iron capable of affording correct in- 
formation of the quantity of oxide of iron that may be present 
in a solution : in doing which I hope to shew that this opinion 
is erroneous. 
Remarks on the objections made to the use of the ferruretted Chy~> 
azate of Potash as a test for the quantity of Iron in Solutions. 
These objections I find very well stated by Dr. Marcet, 
in his Chemical Account of an aluminous Chalybeate Spring 
in the Isle of Wight, as follows : 
“ The prussiate of potash, however well prepared, is quite 
“ inappropriate when the object is to ascertain the quantity of 
“ iron in solution, its utility being confined to indicating its 
“ presence, it being liable to the objections of precipitating 
“ some earthy substances, particularly alumine, when the mix- 
ture is heated, of being itself decomposed by heat, or of 
‘‘ not separating the iron so as to be retained on the filter or 
“ procured by subsidence, if heat is not applied, or if the iron 
“ is not highly oxidated.'* 
Notwithstanding the authority which an opinion of Dr. 
Marcet's on this subject justly carries with it, I must take 
the liberty of asserting, that although I agree with him in the 
