218 ELEMENTARY AGRICULTURAL CHEMISTRY 



CuSO, + Oallfi, = CuH^Og + CaSO, 

 Copper Lime Copper Calcium 



snlphate hydroxide sulphate 



Yarions strengths have been recommended — usually from 12 

 to 30 lb. of copper sulphate to 100 gallons of water, and from 

 8 to 20 lb. of quicklime. Of the pure substances, 239 parts 

 of sulphate of copper require only 56 parts of quicklime, but 

 in practice, as the lime is never pure and portions of it never 

 dissolve, much more lime has to be employed. The mixing of 

 the lime and copper sulphate must always be done in the cold, 

 and there should always be a slight excess of lime. This can 

 be ascertained by filtering the muddy blue liquid and testing 

 it for dissolved copper or lime. The simplest plan for the 

 former is to immerse a piece of polished steel — a knife blade, 

 for example — in the liquid for a few minutes. If there be 

 excess of copper sulphate a stain of metallic copper will appear 

 on the steel. To show excess of lime in the solution the 

 easiest plan is to breathe on the surface, when the carbon 

 dioxide in the air from the lungs will form a thin scum of 

 carbonate of lime. 



A much-used formula is : 



Copper sulphate . . . , , . 6 lb. 



Quicklime . . , 6 „ 



Water 50 gallons. 



Each of the solid constituents should be dissolved in 25 gallons 

 of water, and then thoroughly mixed together. The mixture 

 should be used as soon after its preparation as possible, since it 

 must be remembered that the effective ingredient, copper 

 hydroxide, or rather basic copper sulphate, is in suspension, 

 not in solution. 



It has recently been shown that the active substance in 

 Bordeaux mixture is not copper hydroxide, but some basic 

 copper sulphate — (several are known to exist, e.g., 4CUO.SO3 

 5CuO.SOy and lOCuO.SOg)— which subsequently on exposure to 



