Dr. Hare’s Improved Eudiometers, 71 
as, according to the theory of volumes, it ought to be only 
120. Fut I have not as yet operated with hydrogen, purer 
than it may be obtained from the zinc of commerce; and 
some allowance must be made for the carbonic acid of the 
air, which may be condensed with the aqueous vapour pro- 
duced by the oxygen and hydrogen. 
fn the invaluable work on the Principles of Chemistry, 
lateiy published by Dr. Thomson, it is suggested, that in 
order to obtain correct results in analyzing the air with the 
hydro-oxygen Eudiometer, more than 42 per cent. of hydro- 
gen should not enter into the mixture. [ am noi as well 
satisfied of the correctness of this impression, as I am general- 
ly with the results of the wonderful industry and ingenuity 
displayed in the work above-mentioned 
If oxygen is to be examined by hydrogen, or hydrogen by 
oxygen, we must of course have a portion of each in vessels 
over the pneumatic cistern, and successively take the requisite 
portions of them, and proceed as in the case of atmospheric 
air. 
B, fig. 1. represents a glass with wires inserted through 
small tubulures, in the usual mode for passing the electric 
spark ; should this method of producing ignition be deemed 
desirable for the sake of varying the experiments, or for the 
purpose‘ of illustration. This glass screws on to the socket 
5, the other being removed. ‘The wires (WW) remain, but 
should be of such a height as not to interfere with the pas- 
sage of the electric spark; and the instrument is operated 
with as usual, excepting the employment of an electrical ma- 
chine, or electrophorus, to ignite the gaseous mixture in lieu 
of a calorimotor. For the travelling chemist, the last men- 
tioned mode of ignition may be preferable, because an elec- 
trophorus is more portable than a galvanic apparatus. 
In damp weather, or in a laboratory where there is a pneu- 
matic cistern, or amid the moisture arising from the respira- 
tion of a large class, it is often impossible to accomplish ex- 
plostons by electricity. 
