12 GARDEN FOES. 



not come in contact with the acid while human beings 

 are present. (See Chapter X., Part I.) 



Carbon Disulphide— A combination of sulphur and 

 carbonic acid. It is highly volatile and poisonous. Must. 

 not be used near a naked light, cigarette, cigar, or pipe. 

 Gives off fumes destructive to insect life when buried in 

 the soil. 



Caustic Soda. — A form of soda possessing caustic 

 properties. The best form of it to use for insecticides is 

 commercial caustic soda (98 per cent, purity). It readily 

 dissolves in cold water, and also absorbs moisture, and 

 becomes soft or liquid when exposed to the air. Requires 

 to be kept in tightl}- closed iron cans. Will burn flesh if 

 permitted to touch it. Should be handled only with pro- 

 tected handis. That sold in powdered forms in tins is 

 best. 



Potassium Carbonate (Carbonate of Potash).— A 

 form of j^otash used for making insecticides for winter use. 

 Commercial potassium carbonate (80 per cent.) is the best 

 form to use. Pearl ash and salts of tartar are other 

 names used for it. The form and strength mentioned is, 

 however, the one to procure and use. It is dearer than 

 caustic soda. 



Quassia. — This consists of chips of yellow wood ob- 

 tained from the trunks of a West Indian tree, named 

 Picrena excelsa. When infused in water it produces a 

 bitter fluid. The bitter extract may be obtained by infus- 

 ing the chips in cold water for twenty-four hours or boiling 

 in water for two hours. Extract of quassia and quassine 

 are concentrated preparations of it. Used in conjunction 

 with soft soap. 



Soft Soap.— This is a preparation of soap obtained by 

 chemically treating oil with potash. The best strength to 



