230 ELEMENTARY AGRICULTURAL CHEMISTRY 



mixture then diluted with water. Additions of ammonia and 

 of soap to the liquid are sometimes made, and are said to 

 increase efficiency. For fumigation the powder is scattered 

 on hot coals or on a hot metal plate ; this, of course, can only 

 be effective in a closed space. 



Several other vegetable products — a.g.^ quassia chips — are 

 used as insecticides, but their importance is not sufficient to 

 justify detailed description here. 



Other insecticides are substances which are more commonly 

 used as disinfectants or antiseptics. To this category belong 

 many coal-tar products — carbolic acid, Lysol, Izal, Je)''es' dis 

 infectant, creasote, and many others. 



Quicklime, calcium oxide, CaO, is sometimes used for killing 

 snails, slugs, caterpillars, &c. It is only effective for this pur- 

 pose when fresh and unslaked, and is best applied as fine 

 powder, dusted on to the slugs or caterpillars. Lime-water, 

 too, is useful as a destroyer of many caterpillars and worms. 

 Lime will only dissolve in water to the extent of about 0-13 

 per cent. — i.e., a gallon of water will only dissolve about one- 

 fifth of an ounce of quicklime. Lime-wash — i.e., about 2 lb. 

 of lime to the gallon of water — is also used as a remedy against 

 scale insects, being applied to the bark of trees. 



(B) For Poisoning the Atmosphere breathed by the 

 Insects 



the principal substances used are the following : 



Carbon Disulphide, CSg, " bisulphide of carbon," a colourless, 

 heavy, very refractive liquid, possessed of a strong, disagreeable 

 odour recalling that of rotten cabbage. When perfectly pure, 

 however, it has a pleasant, ether-like smell. Carbon disulphide 

 is very volatile, and its vapour is very inflammable, becoming 

 ignited, when mixed with air, at temperatures much lower 

 than those required to set tire to most combustibles. A mix- 

 ture of air and carbon disulphide vapour is very explosive, and 

 may be ignited even by a glowing pipe or cigar. The vapour 



