CARBONIC OXIDE, CO. A gaseous com pound of carbon and oxygen. It. does not occur naturally. but may be observed burning with a pale-blue flame in fireplaces and stoves. During the combustion of lower layers of the fuel, the oxygen of the air unites with the carbon of the fuel to form carbonic acid, CO,: and this gas, rising through red-hot coal, has part of its oxygen abstracted by the latter• and, as a re sult, carbonic oxide is produced, which, taking fire on the top of the coals, burns. abstracting more oxygen from the air and re-forming ea• bottle acid, CO,.
Carbonic oxide may be prepared by heating either potassium ferroeyanide or oxalic acid with strong sulphuric acid. It is a colorless gas somewhat lighter than air, in which it burns with a characteristic bluish flame. It is exceed ingly poisonous, forming a chemical compound with the haemoglobin of the blood, and thus pre venting the latter from carrying the oxygen which is necessary for supporting the proce-ses of life. The symptoms of carbonic-oxide poison ing are headache, dizziness, and nausea, which.
if the inhalation of the gas is continued, ter minate in death. Hence the great danger arising from checking the escape of the products of com bustion in stoves and furnaces, or of allowing illuminating gas to escape into rooms. Ordinary coal-gas contains about S per cent., water-gas about 40 per cent., of carbonic oxide. The pres ence of carbonic oxide in the air may he best detected by means of a solution of palladhon chloride: if a cloth moistened with a strong solu tion of this salt is exposed to air containing traces of the poisonous gas, a distinct brown col oration is produced. Among the compounds of car bon, carbonic oxide is the only one in which that element occurs in the divalent state; in all other compounds carbon is quadrivalent. It has, however, been suggested that. on the contrary, the other element (oxygen) contained in it niay he quadrivalent, though it is generally found combined as a divalent element. See VALENCY,