[134] Journal de Physique, tom. xliii. 323. The diminution of volume sustained by nitrous gas during its conversion into nitrous oxide, has never been accurately ascertained; it has generally been supposed to be from two thirds to eight tenths. _b._ Nitrous gas may be converted into nitrous oxide in two modes. First, by the simple abstraction of a portion of its oxygene, by bodies possessing a strong affinity for that principle, such as alkaline sulphites, muriate of tin, and dry sulphures. Second, by the combination of a body with a portion both of its oxygene and nitrogene, such as hydrogene, when either in a nascent form, or a peculiar state of combination. _c._ Each of these modes will be distinctly treated of; and to prevent unnecessary repetitions, I shall give an account of the general manner in which the following experiments on the conversion of nitrous gas into nitrous oxide, have been conduced. Nitrous gas, the purity of which has been accurately ascertained by solution of muriate of iron, is introduced into a graduated jar filled with dry mercury. If a fluid substance is designed for the conversion of the gas into nitrous oxide, it is heated, to expel any loosely combined air which might be liberated during the process; and then carefully introduced into the jar, by means of a small phial. After the process is finished, and the diminution accurately noted, the nitrous oxide formed is absorbed by pure water. If any nitrous gas remains, it is condensed by solution of muriate of iron; other residual gases are examined by the common tests. The quantity of nitrous oxide dissolved by the fluid is determined by a comparative experiment; and the corrections for temperature and pressure being guessed at, the conclusions drawn. If a solid substance is used, rather more nitrous gas than that designed for the conversion, is introduced into the jar. The substance is brought in contact with the gas, by being carried under the mercury; and as a little common air generally adheres to it, a small portion of the nitrous gas is transferred into a graduated tube, after the insertion, and its purity ascertained. In other respects the process is conducted as mentioned above. II. _Of the conversion of Nitrous gas into Nitrous Oxide, by Alkaline Sulphites._ The alkaline sulphites, particularly the sulphite of potash, convert nitrous gas into nitrous oxide, with much greater rapidity than any other bodies. At temperature 46°, 16 cubic inches of nitrous gas were converted, in less than an hour, into 7,8 of nitrous oxide, by about 100 grains of pulverised sulphite of potash, containing its water of crystalisation. No sensible increase of temperature was produced during the process, no water was decomposed, and the quantity of nitrogene remaining after the experiment, was exactly equal to that previously contained in the nitrous gas.