232 
ON THE IODIDE OF LEAD. 
aside for twenty-four hours. The whole of the iodine has 
then disappeared, and only the excess of lead is left ; this is 
coated with a yellowish-white substance of a crystalline 
appearance, which is the potassio-iodide of lead. To obtain 
the iodide of lead which this compound contains, it suffices 
to agitate it with water, which decomposes it into iodide of 
potassium and iodide of lead. The dissolved nitrate of lead 
is then poured into the liquid, which decomposes the whole 
of the alkaline iodide. 
The above quantities should give, according to theory, 
32.07 grms. iodide of lead ; they furnished 31.40 — 31.45. 
This iodide is slightly shining, and of a pale lemon color. 
When seen alone, it appears satisfactory ; but when com- 
pared with the iodides obtained by the previous processes, 
a difference is perceptible, which is far from being to its 
advantage. 
Having found by experiment that the iodide of lead pre- 
pared with the iodide of potassium was of a beautiful lemon 
color, I was lead to imagine, from the result obtained by M. 
Thevenot's process, that since about three-sevenths of the 
product derived from the decomposition of the iodide of 
potassium were of a fine quality, the four-sevenths furnished 
by the decomposition of the double salt by water must be 
of a far less lively color. Experiment confirmed this sup- 
position ; in fact, the iodide so obtained is of so pale a yel- 
low tint that one might be led to think it consisted in 
greater part of oxy-iodide. Moreover, its fatty appearance 
is not at all pleasant to the sight. I have repeated this 
experiment several times, and always with the same results. 
In these experiments the weight of the iodide produced 
from the decomposition of the potassio-iodide of lead by 
water alone was on the average 17.80; theory requires 
18.20 grms. 
From these results I conclude, that, in the preparation of 
the iodide of lead, the nitrate of lead, on account of the 
greater product, is more economical, notwithstanding its 
