ZU ELEMENTARY AGRICULTUIIAL CHEMISTRY 



employed as a preservative of food-stuffs— e.^., milk, cream — 

 and in surgery. 



Borax, 'Na^BftjAORfl, is used for similar purposes, and 

 sometimes as a poison for cockroaches. 



Salicylic Acid, Q^HlOWj.COOB., is also sometimes added as 

 a preservative to milk, cream, canned fruits, fruit syrups, &c. 



II. Fungficides. — A fungicide is a plant poison — in fact, 

 a disinfectant — but used under such conditions that while 

 destructive to the low forms of plant-life — the fungi — it does 

 not injure the higher plants. In fact, a fungicide might be 

 defined as a differential plant poison, strong enough to kill 

 some forms of plant-life, but too weak to destroy others. 



A fungicide is usually employed to destroy micro-organisms 

 which are liable to attack cultivated plants, and may be applied 

 to the seed, stem, or foliage, as the case requires. Amongst 

 the substances used as fungicides the following are the most 

 important : 



{a) Copper Salts. — These salts are, when in solution, very 

 injurious even to the higher plants. The starting-point of 

 nearly all copper fungicides is copper sulphate, or " blue 

 vitriol," CuSO^.SHgO. This is a blue crystalline substance 

 of specific gravity 2-28, readily soluble in water to a blue 

 solution. 



100 parts of water at 0° 0. dissolve 31-6 parts of the salt. 

 10° „ 37-0 „ 



20" „ 42-3 „ 



100° „ 203-3 „ „ 



A 2 per cent, solution of the salt has a specific gravity of 

 1-0126, a 4 per cent, solution 1*0254, and a 6 per cent, solution 

 1-0384. 



A solution of copper sulphate has long been used iot 

 ** pickling " seed wheat for the prevention of the fungoid 

 diseases smut^ rust and hunt. A common practice is to 

 thoroughly wet each quarter of wheat with 2 gallons of 

 water in which 2 lb. of "blue vitriol" has been dissolved. 



