Dr. Henry's Additional Experiments 
has attracted moisture, either from the atmosphere or the 
mercury, and is then owing to a condensation of a part of the- 
gas. 
Essentially, the changes produced by electrifying muriatic 
acid over mercury are those which I have stated ; viz. a con- 
traction of the volume of the gas, the formation of muriate of 
mercury (calomel), and the evolution of hydrogen. Recent 
experiments, also, have confirmed the accuracy of the obser- 
vation,* that when a certain effect has been produced by elec- 
tricity, nothing is gained by continuing the process ; for neither 
is more hydrogen evolved, nor can the contraction of bulk be 
carried any farther. 
I have lately applied, to experiments on muriatic acid, an 
apparatus which I used advantageously for the analysis of 
ammonia.-f It consists of a spherical glass vessel, into which 
are hermetically sealed two small tubes containing platina 
wires, the points of which approach within the striking dis- 
tance. To the globular part is attached a neck, which may 
be closed, as occasion requires, either by a glass stopper or by 
a metal cap and stop-cock. Into a vessel of this kind, I in- 
troduced 4 ,j cubic inches of muriatic acid gas, and passed 
through it 3000 discharges from a Leyden jar ; at the close 
of the process, no traces of moisture could be perceived on 
the inner surface of the vessel, nor could I discover, on opening 
the stopper, that any change of bulk had taken place. After 
absorbing the unchanged muriatic acid gas by a small quan- 
tity of water, a volume of gas remained, in which there were 
present 100 measures (each equal to one grain of mercury) 
of oxymuriatic acid gas, and 140 measures of hydrogen. Two 
• Phil. Trans. 1800. p. 192. f Ibid. 1809. 
