The chief are chlorine, sulphurous-acid gas, nitrous-acid gas, and hydrochloric-acid gas. When diluted, they admit of being inhaled; not so when pure.

Chlorine.—This gas has a greenish-yellow color, and a powerful suffocating odor. It is used to fumigate buildings, being a valuable disinfectant. Chlorine is employed by the calico-printer and paper-maker for its bleaching properties. The men who work in an atmosphere slightly impregnated with it suffer from dyspepsia, but are long-lived, and it has been supposed to be actually beneficial to consumptives. Any attempt to inspire chlorine in its concentrated state would at once prove fatal by closing the glottis and causing asphyxia. When diluted it excites excessive irritation of the air-passages, cough, difficulty of breathing, and inflammation.

In poisoning by chlorine, the inhalation of a small quantity of sulphuretted hydrogen appeared to afford relief in a case reported by Christison, but with that, or any other of the irritant gases, our treatment must chiefly consist in the instant removal of the sufferer to pure air. Then the cautious inhalation of ammonia, sulphuric ether, or the vapor of warm water, will be useful.

Sulphurous Acid Gas is one of the products formed by the combustion of ordinary coal. It possesses bleaching and antiseptic properties; and is very irritating when inspired.

Nitrous Acid Gas is a very violent poison when inhaled, producing inflammation of the lungs, &c. It has proved fatal in several instances, when given off by nitric acid.

Hydrochloric Acid Gas is irrespirable in its concentrated state, and when diluted produces great irritation of the lungs and air-passages. This gas, which is a waste product in the manufacture of washing soda, is the chief cause of the barrenness which surrounds soda works where it is allowed to escape, it being extremely destructive to vegetable life.

Ammonia.—It has been already noticed (p. 48) that the vapor of ammonia is poisonous, exciting inflammation of the larynx, bronchitis, and pneumonia. Serious symptoms have sometimes arisen from its indiscriminate application in cases of syncope, &c.