386 Description of an Eudiometer. 
_ the external air rushes into the instrument to 
supply the vacuum. 7 
All these objections, it occurred to me, 
after using the apparatus two or three times, 
might be obviated by substituting a bottle of 
caoutchouc or elastic gum, the sides of which, 
by collapsing as the absorption goes on, must’ 
place the included gas under an uniform de- 
gree of pressure during the whole experi- 
ment.* As a neck to the elastic bottle, for 
* Tt would be unjust to Mr. Pepys, who has benefited 
chemical science by the invention of a variety of, useful 
apparatus, not to state that he published the first account 
of an instrament, in which a bottle of elastic gum is used 
for containing the eudiometric liquid. (Phil. Trans. 1807.) 
As in his apparatus, however, the liquid is injected from 
the elastic bottle into the graduated tube, no contrivance 
was necessary for facilitating the return of the gas from the 
former into the latter; and his eudiometer, therefore, is 
adapted only for those liquids, which, like the solution of 
nitrous gas in sulphate of iron, act by a very moderate 
degree of agitation. The liquid, which I prefer, on ac- 
count of the greater cheapness and facility of making it, is 
prepared by boiling a little quicklime, sulphur, and water, 
together ina Florence flask, decanting the clear fluid, and 
shaking it strongly in a bottle about three-fourths filled 
with it. To effect the absorption of oxygen gas by this 
liquid, especially towards the last, when it bears a smatl 
proportiog to any other gas with which it is mixed, brisk 
and long continued agitation is necessary. 
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