MEMOIR OF THE LATE DR. HENRY. 111 
In the same interval (1800) he also made pub- 
lic through the Philosophical Transactions, some 
experiments on the Muriatic Acid Gas. This 
memoir is one of peculiar interest, both as re- 
calling the state of chemical doctrine, anterior 
to the grand discoveries of Davy, and as mark- 
ing the influence of pre-conceived theories on 
the interpretation of facts. Oxygen was then 
regarded as the sole principle of acidity, and the 
muriatic acid was consequently supposed to be 
constituted of oxygen, associated with an un- 
known radical. It was in the hope of detach- 
ing this imaginary element from oxygen, that 
Dr. Henry exposed the muriatic acid gas, both 
alone, and mingled with gaseous matter possess- 
ing a strong affinity for oxygen, to repeated 
electrical discharges. When the muriatic acid 
gas was electrified alone over mercury its vo- 
lume was uniformly diminished, hydrogen gas 
was disengaged, and a white deposit was collec- 
ted, which proved to becalomel. The decrease 
of volume and the formation of calomel were 
much more considerable, when the electric dis- 
charges were passed through a mixture of oxy- 
gen and muriatic acid gas. When the electriza- 
tion was performed without the presence of mer- 
cury, in a glass tube, closed by stoppers, each per- 
forated with platina wire, chlorine was evolved 
