INORGANIC POISONS 241 



by blowing air through a copper pipe into the copper sulphate 

 and through any pipe into the outer cooling water. The 

 air incidentally helps to oxidize the ferrous sulphate in the 

 crude copper sulphate and prevents its crystallization ; 

 whilst in the outer vessel the air stream evaporates some of 

 the water with a lowering of temperature and economy 

 of cooling water. The water in the outer cooler must in 

 the end be replaced by cold water to reduce the temperature. 

 By these means a very fine grained crystal almost free from 

 iron can be obtained. These fine crystals dissolve readily 

 even in cold water. 



Solutions varying from 2-5 % are used for " pickling " 

 corn to prevent attacks of " rust " in wheat and other similar 

 fungoid parasites. vSolutions of the same strength are used 

 to destroy " charlock," " runch," or wild mustard. About 

 4070 galls, of 3 or 4 % copper sulphate solution are 

 sprayed over an acre of infested wheat, barley or oats when 

 the charlock begins to come into flower. Little harm is done 

 to the corn, but the charlock is burnt up and quickly dies. 



Copper Compounds. Except the cereals, most plants 

 are injured by copper sulphate unless some other substance 

 is added. As a rule the additional material is basic and is 

 added in sufficient quantities to precipitate the copper from 

 solution. Burgundy mixture is made from copper sulphate 

 and sodium carbonate and is applied as a spray to potato 

 plants about July, followed by a second application a few 

 weeks later. For spraying one-third of an acre, 4 Ibs. 

 of sulphate of copper are stirred up with about ten galls. 

 of water in a wooden barrel, capable of holding 40 galls., 

 and then diluted to 35 galls. In a separate vessel, 5 Ibs. 

 of washing soda are dissolved in 5 galls, of water and the 

 mixture slowly poured, with agitation, into the solution in 

 the barrel. Burgundy mixture is of a bright blue colour 

 and only settles slowly ; when a day old it becomes green 

 and settles. The mixture should be sprayed in the blue 

 colloidal form, when it adheres well to the leaves of the 

 potato plant. 



Bordeaux mixture is made by slaking 2 pounds of freshly 

 v. 16 



