Page:Outlines of Physical Chemistry - 1899.djvu/29

 of Wood's metal). If the bulb is sealed, the point is broken off just before it is allowed to fall into a.

Certain solids can be introduced without any bulb, in the form of compressed cylinders.

4. In order to prevent breakage by the fall of the small bulb a protective layer of asbestos is put into the bottom of a.

5. The substances most often employed for the heating bath are : chloroform, benzene, water, commercial xylene, aniline, ethyl benzoate, thymol, amyl benzoate, diphenyl- amine, phenanthrene, mercury, sulphur, &c. ; an air bath may also be used (L. Meyer). For working at very high temperatures the apparatus a b c is made of platinum or porcelain and is heated by means of a Perrot gas furnace (special model).

6. As some vapours are attacked by air it is necessary to fill the apparatus, before the experiment is made, with an indifferent gas, such as carbon dioxide, nitrogen, or hydrogen. In these cases a modified form of the apparatus is used.

7. It is to be noted that the dilution of a vapour by another gas favours the decomposition of molecular associations. Consequently, V. Meyer's method often leads to vapour densities which are smaller than those obtained by Dumas 9 method. Such is the case for aluminium chloride, sulphur, iodine at high temperatures, &c. (see the small book ( Die Praxis der Molekelgewichts- bestimmung,' by JET. Biltz, Berlin, 1898).

��Avogadro's Hypothesis

Gat-Lussac's Law op Volumes. — When two gases combine chemically, there is a simple ratio between the volumes which enter into reaction. If the compound formed is also a gas, its volume bears a simple ratio to the volumes of the constituents. For instance : one volume

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