66 
PATENT INKS, AND SALTS OF GOLD. 
being added to a solution of prussiate of potasli, gives the 
compound of cyanogen and iron, or soluble Prussian blue, 
which has been just described. The addition of water alters 
the character of this iodine solution; without water it turns 
litmus papeF green, and with water it has the usual acid 
reaction, thus apparently confirming Davy's original doubt 
as to the elementary character of iodine. 
2d. I form a neutral iodide of potassium ^ of great purity, 
and wholly free from alkaline reaction, in manner follow- 
ing : — I take the solution which remained over from the 
process first described, after the Prussian blue had been 
precipitated, which solution consisted, as before stated, of a 
neutral iodide of potassium, with iodide of iron in excess; 
and I get rid of that excess by the well-known processes of 
fusion and crystallization. The result is an iodide of po» 
tassium, which is as pure as when iodine and potassium 
are made to act directly on one another, and is perfectly 
free from the alkaline reaction on turmeric paper, which 
invariably characterizes the most careful preparations of 
this salt when carbonate of potassa is employed (as usual) 
in its manufacture. It is also much less deliquescent than 
the ordinary iodide of potassium of commerce, and, on ac- 
count of its great purity, much to be preferred in medicinal 
preparations. 
Blue Printing Ink^ No. 1. 
3d. I manufacture a blue ink of peculiar intensity, and, 
therefore, particularly suitable for printing purposes, by 
using the same materials, and manipulating them in the 
same way as first described, with the exception that for the 
iodine, wherever it is used, 1 substitute bromine, and rub up 
the precipitate in oil. 
4th. I form a bromide of potassium of great purity, and 
wholly free from alkaline reaction, by treating the bromide 
of potassium, which remains over in a state of solution from 
the process last before described, in the same way as the 
