60 On the Came of Chemical Proportions. [Jan. 



with organic or volatile matter, from which it is not easy to get 

 water absolutely free : even the alkaline carbonates employed to 

 precipitate it contain such matters. The consequence has been, 

 that 1 was unable to obtain carbonate of lead wbose carbonic acid, 

 when distilled, had not an empyreumatic odour. 1 shall state, 

 however, those experiments which were the most successful. 



1 dissolved pure nitrate of lead in water distilled over again in a 

 glass alembic, and I divided this solution into two parts, one of 

 which was precipitated by the carbonate of ammonia, the other by 

 the carbonate of soda. 1 found it necessary to add an excess of 

 alkaline carbonate, and to digest tbe precipitate in this excess, 

 otherwise a portion of subnitrate of lead at a maximum is always 

 formed, and the precipitate when decomposed by heat yields 

 towards the end of the process red vapours of nitrous acid gas, in 

 quantity suiTicient to aflect tbe result. Tbe cavbonute of ammonia 

 employed had been prepared from the purest, most colourless, and 

 transparent sal-ammoniac that I could procure by distilling it with 

 pure carbonate of lime heated to redness just before it was mixed 

 with the sal-ammoniac. In one of these experiments I had sublimed 

 the sal-ammoniac in a glass vessel before mixing it with tiie carbonate 

 of lime : but, notwithstanding all tbese precautions, the carbonate 

 of lead obtained by means of this carbonate of ammonia gave out 

 a carbonic acid when heated, which smelled distinctly of tl:e oil of 

 hartshorn. A very small quantity, however, of this oil must have 

 been sufficient to produce the smell : for the result of the analysis 

 by means of carbonate of ammonia dilftrs very little from that by 

 means of carbonate of soda. The carbonate of soda employed was 

 prepared from a very pure supertartrate of soda. Hence it con- 

 tained neither potash, nor sulphate, nor muriate of soda. The 

 carbonate-of lead obtained by means of carbonate of soda yielded 

 a carbonic acid which had less odour than the other, but which was, 

 notwithstanding, mixed with something empyreumatic. 



To analyse these two carbonates I dried them thoroughly on a 

 sand-bath in a heat much above 212°. I tlien put them into small 

 retorts, which were exactly weighed, and which terminated in glass 

 tubes filled with pieces of melted muriate of lime. These tubes 

 were likewise carefully weighed before the experiment. The retorts 

 were then placed upon the fire, and heated till the oxide of lead 

 melted. From these two precipitates I obtained the following 

 results :— 



Precipitate by Ditto by 



ocrhoiiate of soda. carbonate of uinmnnia. 



Carbonic acid l(;-4 i2 16' ti; 



Oxide of lead 8S-33;> 83-333 



Moisture 0-225 O-J-'O 



100-000 100-oro 



The difference between these two results is too small to merit 

 any attention ; yet the empyreumatic odour of the disengaged gas» 



