Circular 21 - Insecticides and Subsidiary Plater ials 65 
gravity of I.025. Pine tar oil is also 
employed in sprays desi;^'ned to kill and to 
repel flies. 
Pine tar oil is a dark brov/n or black- 
ish, heavy, viscous liquid obtained by the 
destructive distillation of v/ood of several 
species of pine trees. It has a sharp taste 
and a somev.hat pronounced burnt or tarry odor, 
definitely pine-like in character. Pine tar 
is heavier than, and only slightly soluble 
in, water. AlTlon§^ the principal constituents 
of this substance are turpentine, resin, 
creosol, phenol, xylene, and other hydrocarbons. 
In raedicine, pine tar oils are chiefly 
used for the treatment of skin diseases and 
respiratory disorders. Industrially, it has 
many u^es including the manufacture of 
automobile tires. 
This oil sells at 20 to 55 cents per 
gallon in 600-pound barrels. 
ror manufacturers and distributors 
see nuiabers 5 and 12 of list at end of this 
circular. 
FraETKRmi 
Pyrethrum consists of dried flovrers or 
buds of plants of any one of three particular 
species of the genus Chrysanthemu m ( P^^rethrum ) . 
These contain compounds knov.71 as pyrethrms I 
and II that are very toxic to insects. Flowers 
are now available from Kenya Colony which will 
average about 1.3 percent pyrethrins. Insect 
powders may be prepared by grinding the flov/ers, 
and used pure or diluted with some inert carrier 
