CHEMISTRY. at 
1. Apparatus for Combining Gaseous Elements. 
Combination of Hydrogen with Oxygen. To ascertain the ratio in which 
these two gases combine, we make use of an instrument termed an eudiometer 
(pl. 31, fig 66). This is especially employed to determine the character of 
a gas with respect 10 its amount of oxygen. The eudiometer is essentially 
a graduated glass tube, into the upper end of which two wires have been 
inserted opposite to each other. A tube of this character is often surrounded, 
excepting two longitudinal strips allowing the graduation to be seen, by a 
metal casing. This tube is first inverted and filled with water, then erected 
under water and raised, so that the lower part of the tube may still be 
immersed, the tube itself remaining filled with water. Pure hydrogen gas 
is now to be introduced into the tube by the ordinary method of manipu- 
lation, filling it to a certain amount, as twelve degrees ; if half this volume 
‘ or six degrees of pure oxygen be now introduced, and the charge of a 
Leyden jar passed through the mixed gases by means of the two metal 
wires, an explosion will take place, sometimes sufficient to shatter the tube. 
If the gases be perfectly pure, the water will immediately rise to the top of 
the eudiometer, the contained gases having all been combined to form 
water. If seven degrees of oxygen had been taken in the above experi- 
ment, then there would have been one degree of oxygen left in the tube 
after the explosion, just as we would have had a portion left of hydrogen 
had this gas entered in greater proportion than the one mentioned. Here 
we perceive that chemical combinations are all definite, and that an excess 
of one ingredient over the proper proportion, is indicated by this excess 
remaining free. 
2. Apparatus for Combining Liquid Elements with Gaseous. 
As already mentioned, mercury and bromine alone of all chemical 
elements, occur in the liquid condition. Mercury can be combined directly 
with gaseous oxygen. If this metal be boiled for several months in a 
matrass (pl. 30, fig. 27), whose neck for this purpose should be several feet 
long, the mercury will be gradually changed into a red crystalline powder, 
which, in 108 parts by weight, contains 100 of mercury and 8 of oxygen. 
It is this oxyde of mercury which by heating is again decomposed into 
mercury and oxygen, and may therefore be used in the preparation of pure 
oxygen. More advantageous processes for obtaining this oxyde are known 
in the arts, more complicated, however, in their character. 
3. Apparatus for Combining Solid and Gaseous Elements. 
Among the gaseous elements, oxygen and chlorine, as also iodine, bromine, 
and sulphur, when converted into vapor by heat, combine with almost 
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