36 Mr. Davy’s Lecture on the Decomposition and Composition 
ammoniacal gas:* a great expansion of the aeriform matter 
took place, and a white substance formed, which collected on 
the sides of the glass tube employed in the process ; and this 
matter, exposed to the action of diluted muriatic acid, effer- 
vesced, so that it was probably carbonate of ammonia. 
A process of another kind offered still more decisive results. 
In this the two mercurial gazometers of the invention of Mr. 
Pepys, described in No XIV. of the Phil. Trans, for 1807, were 
used with the same apparatus, as that employed by Messrs. 
Allen and Pepys for the combustion of the diamond, and these 
gentlemen kindly assisted in the experiment. 
Very pure ammoniacal gas was passed over iron wire 
ignited in a platina tube, and two curved glass tubes were so 
arranged as to be inserted into a freezing mixture ; and 
through one of these tubes the gas entered into the platina 
tube, and through the other, it passed from the platina tube 
into the airholder arranged for its reception. 
The temperature of the atmosphere was 55°; but it was 
observed that no sensible quantity of water was deposited in the 
cooled glass tube transmitting the unaltered ammonia, but 
in that receiving it after its exposure to heat, moisture was 
very distinct, and the gas appeared in the airholder densely 
clouded. 
* The apparatus in which this experiment was made is described in page 214 
Journal of the Royal Institution. The gas was confined by mercury which had been 
previously boiled to expel any moisture that might adhere to it. The ammonia 
had been exposed to the action of dry pure potash, and a portion of it equal in 
volume to 10980 grains of mercury, when acted on by distilled water, left a residuum 
equal to 9 grains of mercury only. So that the gas, there is every reason to believe, 
contained no foreign reriform matter; for even the minute residuum may be accounted 
for by supposing it derived from air dissolved in the water. 
