It will be seen hereafter that very high temperatures are required for the decomposition of nitrous oxide, by most of the combustible bodies, and that in this process heat and light are produced to a very great extent. These agents alone are possessed of a considerable power of action on nitrous oxide; of which it is necessary to give an account, that we may be able to understand the phænomena in the following sections. II. _Conversion of Nitrous Oxide into Nitrous Acid, and a Gas analogous to Atmospheric Air, by Ignition._ _a._ Dr. Priestley asserts, that nitrous oxide exposed for a certain time to the action of the electric spark, is rendered immiscible with water, and capable of diminution with nitrous gas, without suffering any alteration of volume; and likewise that the same changes are effected in it by exposure to ignited incombustible bodies.[167] [167] Vol. ii. pag. 91. The Dutch chemists state, that the electric spark passed through nitrous oxide, occasions a small diminution of its volume, and that the gas remaining is analogous to common air.[168] They conclude that this change depends on the separation of its constituent parts, oxygene and nitrogene, from each other. [168] Journal de Physique, tom. xliii, part ii. pag. 330. They effected the same change by passing it through a heated tube. Dr. Priestley had published an account of similar experiments more than two years before. None of these chemists have suspected the production of nitrous acid in this process. _b._ Nitrous oxide undergoes no change whatever from the simple action of light. I exposed some of it, confined by mercury, for many days to this agent, often passing through it concentrated rays by means of a small lens. When examined it appeared, as well as I could estimate, of the same degree of purity as at the beginning of the experiment. _c._ A temperature below that of ignition effects no alteration in the constitution of nitrous oxide. I passed nitrous oxide from a retort containing decomposing nitrate of ammoniac, through a green glass tube, strongly heated in an air-furnace, but not suffered to undergo ignition. The gas, received in a water apparatus exhibited the same properties as the purest nitrous oxide; some of it absorbed by water, left a residuum of not quite one thirteenth. _d._ The action of the electric spark for a long while continued, converts nitrous oxide into a gas analogous to atmospheric air, and nitrous acid. I passed about 150 strong shocks from a small Leyden phial, through 7 ten grain measures of pure nitrous oxide. After this it filled a space rather less than six measures: the mercury was rendered white on the top, as if it had been acted on by nitric acid. Six measures of nitrous gas mingled with the residual gas of the experiment, over mercury covered by a little water, gave red fumes, and rapid diminution. In five minutes the volume of the gases nearly equalled ten. Thermometer in this experiment was 58°.