CHEMISTRY. 9 
constructed of copper; B the head, which, with the tube C and the cooling 
vessel EE, may more economically be constructed of tin. The space for the 
fire is at G. As soon as a liquid boils in the alembic A, its vapors ascend 
into the head B, and thence through the tube C into the cooling apparatus. 
The latter consists of a wooden box, DD, in which is set a tin cylinder, 
EE, running out below into a tube, F. Into the cylinder, EE, is inserted 
a smaller tin cylinder, eeee, closed below, down whose middle passes the 
tube of a funnel, a, reaching almost to the bottom. An uninterrupted 
stream of cold water is allowed to flow into the under cylinder through the 
funnel, a, and its tube. The vapors from the alembic, which enter the 
space inclosed between the walls of the inner and outer cylinder, are cooled, 
on the one side, by the fresh water introduced through the funnel a, and, 
on the other, by the water in the box DD. Fresh cold water is introduced 
into the bottom of this box by means of the funnel, b, and the pipe, c. As 
the water in the inner cylinder, eeee, becomes heated, it flows through a 
small pipe into DD, and thence, with the heated water of DD itself, out at a. 
It will be remembered that water, as it becomes heated, becomes 
specifically lighter, for which reason the warmest water will always occupy 
the highest position in the vesse] containing it. The cold water, also, 
introduced through the funnels, occupies the lowest part of the several 
vessels, and displaces the heated water previously occupying that same 
position. The vapors from the body of the apparatus are condensed so 
perfectly by this arrangement, that a liquid, hardly lukewarm, flows out as 
the result through the pipe F. 
All distilling apparatus, properly so called, have for their end the recovery 
of the liquid vaporized. It often happens, however, that our only object is 
to collect some solid dissolved in a liquid. Thus, when we wish to obtain 
solid salt from a solution of salt and water, the water is here of no use. In 
such cases, instead of distilling vessels, we make use of very shallow and 
wide vessels, in which the liquid may come as much as possible in contact 
with the air. Evaporating dishes of this kind are represented in 
pl. 30, figs. 35 and 36. 
4. Instruments for Investigating Matter which is Gaseous at Ordinary 
Temperatures. 
We have already gone into some detail upon the methods of converting 
solids into liquids, and liquids into the gaseous condition. It remains to see 
whether the reverse may not be possible, whether it does not lie in our power 
to convert a gas into a solid, or at least into a liquid. With the means 
commanded by modern chemistry, there are now only three elementary 
substances which cannot be changed from their gaseous condition : oxygen, 
hydrogen, and nitrogen. The method of condensing gases will readily 
suggest itself from what has been said on the subject of boiling. Since the 
cause of the gaseous condition of a solid or liquid is to be found in the 
combination of heat rendered latent, and since, when this latent heat is 
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