PART VI. CHEMICAL INSECTICIDES AND 

 FUNGICIDES 



SECTION I. INORGANIC POISONS 



IN addition to the need for supplying the plant with ferti- 

 lizing ingredients, it is often found desirable to protect the 

 crop from attack by insects, fungi or other living parasites. 

 Beside the substances coming under that heading there are 

 also some poisons employed either in the manufacture of 

 dairy products, or during the process of cleaning on the 

 farm, or on other special occasions connected with farming. 

 Mercury. Excepting as mercuric chloride (corrosive 

 sublimate), little use is made of mercury on the farm. In 

 the ordinary preparation of mercuric chloride, mercury is 

 first heated with sulphuric acid, the resulting cake mixed 

 with salt, dried with precautions to avoid poisonous fumes 

 and finally sublimed. Great care is taken to avoid admixture 

 with traces of calomel and sulphuric acid, but for agricultural 

 purposes the presence of these impurities is of no conse- 

 quence. Solid mercuric chloride is not suitable for use on 

 a farm, but solutions are required for disinfection when cases 

 arise of abortion or other highly infectious disorders. The 

 best strength of solution varies from i part of mercuric 

 chloride in 500 of water to i part in 5000, to which may 

 be added a little acid. For practical use, stronger solutions 

 are kept ready to hand in glass bottles which should be 

 provided with rubber stoppers attached by string to the 

 bottle, to prevent loss, or more important still, to prevent 

 the mercury-contaminated stopper being put into a wrong 

 bottle. A good standard article is made from 5 parts of 

 mercuric chloride, 5 parts of common hydrochloric acid 

 and 100 parts of water. The same strength of solution 



