6S9 
termed triple Prussiates, 
experimental facts cited as the causes for it, yet that I draw 
a different conclusion from his, because, instructed by my 
experiments on the nature of the triple prussiates, I find that 
all those inconvenient effects are easily prevented from ensu- 
ing ; and I therefore conclude that the ferruretted chyazate 
of potash is in general the most appropriate test of the quan- 
tity of iron in solution of any employed in chemistry ; the use 
of it for this purpose only requiring attention to the following 
facts. 
ist. That if the ferruretted chyazate of potash after being 
dissolved in water gives immediately a blue precipitate by the 
addition of muriatic acid, it is not pure, and will give a falla- 
cious result. 
2dly. That if this salt, however pure, be added in excess to 
a solution of iron containing an excess of acid, and then heated, 
the Prussian blue thrown down will weigh more than it ought, 
because some is furnished by the decomposition of the ferru- 
ginous acid of that part of the salt which has been added in 
excess. 
3dly. That Prussian blue,, even after it has been formed, is 
materially acted upon by a mixture of nitric and muriatic 
acids, and in some degree by the muriatic acid alone at a 
boiling heat. 
4thly. That Prussian blue, when precipitated, often carries 
with it sulphate of potash derived from the liquid from which 
it is thrown down ; and that this sulphate adheres to it so 
obstinately that several washings with water acidulated with 
sulphuric acid, are necessary to detach it. 
5thly. That if the solution to which the test is applied con- 
tains besides iron, barytes, alumine,. oxide of copper, or any 
