Self-regulating Reservoir, for Gases. 141 
was contrived by Gay Lussac. I had employed the same 
principle, however, when at Williamsburgh, to moderate the 
evolution of carbonic acid, before I had read of Gay Lussac’s 
aj 
pparatus. 
I prefer the modification above described. In the first 
place, it is internally more easy of access, for the purpose of 
cleansing : secondly, it is h bet 
ing sulphuret of iron, or marble, for generating sulphuretted 
hydrogen, or carbonic acid gas ; and thirdly, by raising the 
bell glass, the pressure may be removed. 
In the other form, the pressure on the gas is so great, that, 
unless the tube, the cock, and their junctures, be perfectly 
tight, there must be a considerable loss of materials ; since 
» by 
"permitting the acid to reach the zinc, or other materials em- 
