340 SMITH'S INTERMEDIATE CHEMISTRY 



Physical Properties of Carbon Monoxide. Carbon monox- 

 ide is a colorless, odorless, and tasteless gas. It is a little lighter 

 than air (mol. wt. 28), and is very slightly soluble in water. It is 

 difficult to liquefy. Its boiling-point, when liquid, is 190, 

 close to that of liquid air. 



Chemical Properties. When set on fire, the gas burns in 

 air or oxygen with a blue flame. Carbon dioxide is formed, and 

 the presence of the latter may be shown with lime-water (p. 336) : 



2 -*2C0 2 . 



On account of this property, carbon monoxide reduces the oxides 

 of the less active metals, such as those of iron and of the metals 

 below iron in the order of activity. Commercially, the ores of 

 iron are reduced by this gas (essentially producer gas) in the blast 

 furnace. The oxides of the metals above iron are not reduced. 



Physiological Properties. The gas is an active poison, and 

 1 volume in 100,000 volumes of air produces symptoms of poison 

 ing, while one volume in 750 to 800 volumes produces death in 

 about thirty minutes. The gas combines with the haemoglobin 

 of the blood corpuscles, forming a stable compound, and thus 

 preventing the absorption of oxygen by the blood (p. 34). This 

 gas is the chief poisonous substance in illuminating gas. The 

 poisonous effect of tobacco smoke, particularly when inhaled, is 

 due mainly to the carbon monoxide produced by the necessarily 

 incomplete combustion. 



Combustions or explosions in confined spaces (such as in a mine- 

 shaft, or in the interior of a warship during an engagement) may 

 cause many deaths through CO poisoning. Gas masks for use 

 in rescue work in such cases are fitted with canisters containing 

 a mixture of metallic oxides, as Mn0 2 , CuO, Co 2 O 3 and Ag 2 O (hop- 

 calite). A mixture of this kind acts catalytically, any carbon 

 monoxide passing into the canister being oxidized to carbon 

 dioxide by the oxygen of the air. 



