Nitrous Oxide (X,()), formerly called protoxide of nitrogen or laughing gas, a chemical compound which may be prepared by the action of equal parts of nitric and sulphuric acid, diluted with ten parts of water, upon metallic zinc. Sulphion of the sulphuric acid unites with the metal, and the nascent hydrogen deoxidizes the nitric acid. The reaction is represented in the following equation: 8HS04 + 2IIN03 + 8Zn-=8ZnS04 + 5H20 + N,0. The gas obtained in this way is impure, and it is better to procure it by decomposing nitrate of ammonia. The salt being placed in a retort and a gentle heat applied, it melts at 220°, and at 482° or 500° is converted into nitrous oxide and water (H4N, N03-=2H20 + N20). Nitrous oxide is a colorless transparent gas, having a specific gravity of 1*527. According to Bun-sen, 100 volumes of water at 32° dissolve 130 of the gas, at 59° 77 volumes, and at 75° 60 volumes. It should therefore be collected over warm water. It has a faint sweetish taste and smell.

At a temperature of 45° a pressure of 50 atmospheres reduces it to a colorless liquid of specific gravity 0'9004, having a boiling point of - 133°. The liquid nitric oxide mixed with sulphide of carbon and placed in vacuo caused, according to batterer, a reduction of temperature to - 220°, the greatest degree of cold that has yet been attained. It supports combustion with a power approaching that of oxygen. When respired it produces an exhilaration of the whole system, with a disposition to muscular exertion; and there is often a state of great mental exaltation, and a disposition to uncontrollable laughter, from which it has received the name of laughing gas. It has the power of diminishing and destroying the sense of pain, a fact known to Sir Humphry Davy (see Anaesthetics), and if its administration is continued of producing a state of unconsciousness. It is used for this purpose in the extraction of teeth, and also in surgical operations, although sulphuric ether or chloroform is usually preferred.