ORGANIC POISONS 253 



hot treatment in an open tank. Such mixtures can also be 

 painted on with a brush. For the eniulsification processes, 

 a creosote should be used which is rich in tar acids and poor 

 in hydrocarbons. 



Sulphonated creosotes are also used. For this purpose 

 creosote is heated with 2 or 3 % of its bulk of strong sul- 

 phuric acid. After sulphonation a creosote will mix with 

 water to an emulsion. Sulphonated creosotes can also be 

 applied with a brush for fence work. 



Naphthalene. During the process of distilling coal tar, 

 there is a period, a little over 200 C. (400 F.), when 

 the distillate solidities in the condenser. Also, on cooling 

 many distillates, naphthalene crystallizes out. The crude 

 naphthalene so obtained is sometimes known as " creosote 

 salts," and is of the consistency of brown sugar. All forms 

 of naphthalene are slightly greasy and apt to stick together 

 in lumps. To avoid stickiness during application on the 

 land, naphthalene is often mixed with some dry material, 

 such as boiler ashes, waste lime, sawdust, etc. For this 

 purpose the naphthalene should be melted and poured on 

 to its own weight of ashes or other drying material and then 

 ground in a mill. Insects dislike naphthalene intensely and 

 try to get away from it as fast as they can. If unable to 

 avoid it they usually ultimately succumb to its effects. 



Gas Lime. This well-known means of destroying many 

 pests in the soil is now only produced in small amounts 

 owing to improved methods of gas purification. It has been 

 described on p. 54. 



Tobacco. Waste tobacco is used for insecticides. The 

 strength varies to a great extent. 2 Ibs. of waste tobacco 

 added to 10 galls, of water makes a good spray. Strong 

 extracts can also be prepared by boiling up tobacco and 

 water at the rate of 2 Ibs. to the gallon. After straining 

 off the liquor, the tobacco should be extracted with a further 

 supply of water ; the weaker extract obtained is then used to 

 extract fresh tobacco. In this way more economical use 

 can be made of waste tobacco. 



Quassia. The chips of wood of Picraena excelsa are 



