IODINE FOR HYDROGEN IN ORGANIC COMPOUNDS, &C. 53 



■ 



. , romeconate of lead is readily obtained as a fine colourless amorphous 



. ,, „ 'Jd. on mixing alcoholic solutions of the acid and acetate of lead, with the 

 in. thp to, ' ° 



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 10 H 2 10., as shown by the subjoined cal- 

 culation: — 





Experiment. 





Calculation. 





Carbon, . . 



17-612 



C 10 



60 



Hydrogen, . 





•587 



H 2 



2 



Oxygen, . . 





11-743 



5 



40 



Iodine, . . 





37-309 



I 



127-1 



Oxide of lead, . 



. 3303 



32-749 



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 



