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 Dry air = 1 Oxygen 1 Nitrogen 1 Hydrogen 1 Chlorine 60 Bromine 160 Hydrochloric acid 1005 Carbonic oxide 750 Nitric oxide 1590 Nitrous oxide 1860 Sulphide of hydrogen 2100 Ammonia 7260 Olefiant gas 7950 Sulphurous acid 8800 Thus, for a tension of an inch of mercury, the absorption of ammonia exceeds that of air more than 7000 times; the action of olefiant gas is 7950 times, and that of sulphurous acid 8800 times, greater than the absorption of air.