Carbon Monoxide, CO

Carbon monoxide, also known as Carbonic oxide, is found amongst the gases evolved from active volcanoes, and occurs in small quantity in some minerals, and in diamantiferous earth at Kimberley. This gas is also present in coal-gas to the extent of 6.12 per cent., and is formed simultaneously with carbon dioxide in the combustion of carbon, as well as by the reduction of the latter gas when it passes over red-hot carbon:

CO₂ + C = 2CO.

Hence carbon monoxide is formed in a coke fire, on the top of which it burns with a pale flame; and it is produced in various metallurgical operations in which coal or coke is used as fuel, as, for instance, in the blast-furnace. It is an important constituent of water-gas, made by passing steam over carbon at 1000° C.:

C + H₂O = CO + H₂;

and of producer gas formed by passing air, together sometimes with steam, through red-hot carbonaceous material. Carbon monoxide is an intermediate product, also, in the combustion of hydrocarbons, and is found in the interconal gases of the Bunsen flame.

Carbon monoxide, or carbonic oxide as it is sometimes rather erroneously called, was discovered in 1776 by Lassone, who obtained it during the reduction of zinc oxide by charcoal. On account of the blue flame with which it burns, this gas was at first mistaken for hydrogen, and its production was cited by Priestley in support of that version of the phlogiston theory which supposed that metallic calces contain water, and that inflammable air, i.e. hydrogen, is phlogisticated water. In 1800 Cruikshank showed that when the gas burns it produces no water, but an equal volume of carbon dioxide; and in 1802 Clement and Desormes confirmed Cruikshank's observation, and also showed that the same gas is produced when carbon dioxide is passed over red-hot charcoal. In his New System of Chemical Philosophy (1808) Dalton showed that "carbonic oxide is a binary compound consisting of one atom of charcoal and one of oxygen..." and that "carbonic acid is a ternary compound... consisting of one atom of charcoal and two of oxygen." Thus the nature and composition of carbon monoxide were definitely established.