IODINE FOR HYDROGEN IN ORGANIC COMPOUNDS, &C. 53 
cantesaiaitlt comeconate of lead is readily obtained as a fine colourless amorphous 
in the fr. on mixing alcoholic solutions of the acid and acetate of lead, with the 
addition of a small quantity of ammonia. As thus prepared, it is apt to carry 
down an excess of oxide of lead, which is easily removed by warm acetic acid. 
It is of sparing solubility in alcohol or water, and becomes highly electrical when 
rubbed. This salt, contrary to expectation, evolves free iodine, like the acid 
itself, when burned with chromate of lead; but the phenomenon is probably 
owing to the decomposition of the salt taking place at a temperature much 
lower than that sufficient to enable the iodine to combine with lead. For this 
reason I contented myself with a determination of its oxide of lead, which was 
effected by igniting the salt, after the addition of a few drops of concentrated 
sulphuric acid :— 
6:15 grains substance, dried in the air, gave 
2°76 .-- sulphate of lead. 
corresponding to the formula, PbO, C,, H, 10,, as shown by the subjoined cal- 
culation :— 
Experiment. Calculation. 
SS —— 
Carbone sa Mee 17°612 Cio 60 
Hydrogen,. . . ae 687 H, 2 
Oxygen, .. . Be 11:743 0, 40 
Iodine, . . . . xe 37:309 I 127-1 
Oxide oflead,. . 33:03 82-749 PbO 111-56 
100-00 100-000 340°66 
I have already mentioned, that when the quantity of chloride of iodine em- 
ployed is larger than is requisite for the production of iodopyromeconic acid, the 
fluid acquires a yellow colour, due to the presence of another compound, of very 
remarkable characters, produced by a further decomposition of pyromeconic acid, 
and to which I gave the name of iodomecone. When potash is gradually added 
to the fluid, after separation of the iodopyromeconic acid, a blackish precipitate 
immediately falls, which rapidly dissolves on agitation of the fluid, while a peculiar 
odour is evolved. After the addition of the potash has been continued for some 
time, a point is reached at which the precipitate assumes a lighter colour, is no 
longer dissolved, and is not increased by further addition of the alkali. The 
precipitate is then filtered from the alkaline fluid, washed with cold water, and 
purified by repeated crystallization from boiling alcohol. By subsequent experi- 
ments, I ascertained that it was easy to convert pyromeconic acid entirely into 
this compound, by adding a large quantity of chloride of iodine, when the crys- 
tals of iodopyromeconic acid at first formed rapidly disappeared, and carbonic 
acid was evolved. Exactly similar effects are produced by bromide of iodine. 
Iodomecone is obtained in large hexagonal plates of a bright yellow colour 
VOL. XXI. PART I. P 
