ORGANIC POISONS 251 



Petroleum. When petroleum is distilled, a moderately 

 high boiling fraction is used for lighting purposes under the 

 name of paraffin oil or kerosene. Paraffin oil only forms 

 temporary emulsions with water when violently agitated, 

 but by the addition of colloids, or fine precipitates, a semi- 

 permanent emulsion can be obtained. The most con- 

 venient emulsifying agent is soap. A good stock solution 

 can be made by dissolving i Ib. of caustic soda and 

 10 Ibs. of soap in 10 galls. (100 Ibs.) of water, adding 

 10 galls, of paraffin and emulsifying by forcing all the 

 liquid through a finely perforated plate ; a syringe will serve. 

 The stock solution keeps well and can be diluted with 

 10 times its bulk of water when required. The spray 

 can be used on vegetables and fruits, which would be 

 poisonous if mercury, copper, lead or arsenic were used. In 

 a few days the smell of the paraffin disappears. Even the 

 burrowing grub that attacks parsnips can be killed off by 

 this treatment. 



Soap. For destroying aphis even i % of soap is suc- 

 cessful, and for caterpillars 2-3 % will serve. The insecticidal 

 power of the solution can be increased by adding J-J % 

 caustic soda. 



A useful dry soap powder is made by grinding together 

 a hard soap and soda ash. The proportions used vary, but 

 2 or 3 parts of soda ash to i part of soap is a useful 

 mixture. Of such a dry soap, 1-2 Ibs. per 10 galls, 

 makes a useful spray for aphis and many small grubs. 

 This dry soap may also be used in place of the mixture of 

 soap and caustic soda employed with paraffin in the above 

 paraffin emulsion. 



Rosin soaps are very suitable for grinding up with soda 

 ash for making dry powders for spraying. Such preparations 

 are more active than those made from pure fat soaps. The 

 rosin used chokes the breathing pores of small grubs whose 

 cuticle is wetted and injured by the accompanying alkali. 

 Tar acids and other disinfectants can also be introduced into 

 the dry soap mixtures to produce more powerful results. 



Tar Acids. Phenol, cresol and their homologues are all 



