^0 Mr. William Henry’s Experiments on the 
the space occupied before, when one, two, or more additional 
atmospheres were applied. Brisk agitation was now used, as 
long as any absorption took place ; and, into the tube B an as- 
sistant poured mercury, so as to preserve in it the excess of 28 
inches above the level of the mercury in A. The degree erf* 
absorption was known by the scale on A, or, more accurately, 
by the quantity of mercury required to support the elevation of 
28 inches in B. 
By lengthening the column in B to 56 inches, the pressure 
of two additional atmospheres was obtained ; and this was the 
utmost extent to which the addition of weight could be carried, 
without forcing the joint at D. 
When the cock b was opened, and the column in each leg 
thus suddenly fell to the same level, the water, which had been 
previously charged with gas, under a pressure of three atmo- 
spheres, effervesced violently ; but some time elapsed before the 
additional gas, forced in by compression, was wholly evolved. 
These appearances are very striking and amusing; and are well 
calculated for exhibition in a chemical lecture. The apparatus, 
however, I have no doubt, may be greatly improved ; but, at 
the distance of nearly 200 miles from the metropolis, I was 
under the necessity of using such an one as could be con- 
structed by my own hands. 
A considerable improvement in the construction of the appa- 
ratus, which would obviate the expediency of the flexible tube 
D, would be the following. To the lower neck of the vessel A, 
Fig. 1, let a cap and cock, with a female screw, be cemented; 
and let the upper end of the pipe C be terminated by a cock 
with a male screw. Introduce the gas and water, in the manner 
already described ; apply the increased pressure ; and, having 
shut the two additional cocks, unscrew them from each other. 
