In order to ascertain the relation between the density of the gas and the quantity of heat extinguished or absorbed, an ordinary mercurial gauge was attached to the air-pump. The experimental tube was exhausted, and the needle of the goniometer stood at zero. Then, from a graduated glass vessel, measures of olefiant gas, each amounting to the 1/50th of a cubic inch, were successively sent through the drying pipe into the exhausted tube. The amount of the heat absorbed and the depression of the mercurial column corresponding to each measure of gas as it was introduced, was registered from one to fifteen measures. This experiment showed that for very small quantities of gas, the absorption is exactly proportional to the density or tension. One measure of the gas only produced a depression of the mercurial column amounting to the 1/367th part of an inch, or about the 1/15th of a millimetre.
In many of the vapours of volatile liquids, the preceding law only prevails to a certain amount of pressure differing in each case, beyond which increase of tension produces diminished effects. In sulphuric ether the change begins at the eleventh term.
In bisulphide of carbon the law changes after the sixth measure, &c.
In order to adapt the apparatus for experiments on coloured gases, a glass experimental tube 2 ft. 9 in. long, and 2 ft. 4 in. in diameter, was substituted for the brass tube, and, instead of boiling water, sources of radiant heat having a constant temperature of 270° Cent. were adopted.
The following table shows the absorption of a number of gases at a common pressure or tension of one atmosphere.
Dry air = 1 Oxygen 1 Nitrogen 1 Hydrogen 1 Chlorine 39 Hydrochloric acid 62 Carbonic oxide 90 Carbonic acid 90 Nitrous oxide 35·5 Sulphuretted hydrogen 390 Marsh gas 403 Sulphurous acid 710 Olefiant gas 970 Ammonia 1195
The absorptive power of ammonia is so great, that although as transparent in the glass tube as if it had been a vacuum, a length of three feet of it would be perfectly impervious or black to the heat here employed, yet even this does not express the energy which it exhibits under one inch of pressure.
When the relative absorptive actions of gases and vapours is compared, it must be under the same amount of pressure. Hence, for one inch of tension, the absorptive action of