112 MEMOIR OF THE LATE DR. HENRY. 
and detected by the usual test. It is manifest 
that these experiments, had they been justly 
interpreted, were sufficient to establish the true 
view of the composition of muriatic acid gas. Yet 
governed by the theory of acidification then uni- 
versally prevalent, Dr. Henry referred the disen 
gagement of hydrogen to the decomposition of 
water, which was supposed to be still present in 
the gas after a week’s contact with fused chloride 
of calcium. Nor was it until many years subse- 
quently that the simpler theory was firmly estab- 
lished by thegenius of Davy. To the new doctrine, 
Dr. Henry, had, however, the merit of becoming 
an early convert ; and in a supplementary essay, 
published in the Transactions for 1812, he sup- 
plied some important evidence in its favour. 
He showed that the same proportion of hydro- 
gen gas was obtained by electrizing muriatic 
acid gas, whether it had been exposed or not to 
fused chloride of calcium ; and hence concluded 
that the hydrogen was eliminated from the mu- 
riatic acid gas, and not from aqueous vapour. 
He also ascertained, that the muriatic acid gas, 
when completely insulated in a closed glass 
vessel, sustained no change of volume from a 
succession of electrical discharges. This per- 
manence of bulk was made more apparent by 
repeating the experiment in a vessel with a neck 
