REPORT OF THE CHEMIST. 173 



To precipitate a definite amount of copper sulphate, a definite amount of lime is 

 necessary — at least 3-5 ounces of freshly burnt lime for each pound of bluestone. In 

 practice, however, in order to ensure the complete precipitation of the copper, and since 

 impurities always exist in the commercial article, an excess of lime should be used. No 

 element of danger is in this way introduced, as the excess of lime, when using the above 

 formula, is not injurious to foliage. It may be pointed out that air-slacked lime con- 

 tains variable and sometimes large percentages of carbonate of lime, and hence its use 

 for this purpose is not advised. It has occasionally been suggested to use the super- 

 natant lime water which can be poured off from the undissolved lime — lime water in 

 fact. Fifty gallons of such saturated lime water contain only sufficient lime to pre- 

 cipitate (practically) two pounds of copper sulphate. Such a practice would leave 

 copper sulphate in solution. As already remarked, it is owing to the sulphate of lime 

 separating as it is formed, that fresh quantities of lime aie dissolved and can, therefore, 

 react with the copper compound. 



"Well made Bordeaux mixture should be of a deep sky-blue colour. A greenish 

 colour denotes the presence of basic sulphate of copper and an insufficiency of lime. The 

 clear fluid, obtained after filtration or the settling out of the cupric hydrate, should not 

 give a brown colour with potassium ferrocyanide, proving the absence of soluble copper 

 salts. The fluid upon exposure to air should become covered with a thin pellicle of 

 carbonate of lime, indicating the presence of an excess of lime. 



Bordeaux mixture will not keep without deterioration ; changes occur that mate- 

 rially effect its adhesive qualities. Stock solutions of copper sulphate and milk of lime 

 of known strengths may, however, be kept ready for dilution and mixing. They should 

 be preserved from the atmosphere in well corked stoneware jars. 



By the evaporation of the spraying solution the copper is left upon the foliage as 

 the hydrate. 



Copper Carbonate. 



If a solution of sodium carbonate (Na 2 C0 3 , 10H 2 O) be added to one of copper 

 sulphate (CuS0 4 , 5H 2 0), the copper is thrown down as a pale green precipitate. This 

 is " basic carbonate of copper " (a compound containing both carbonate and hydrate of 

 copper), and has the formula, CuC0 3 , CuOH 2 . It dries to a light green, amorphous 

 powder. In the above re-action sodium sulphate (Na 2 S0 4 ) is formed and remains in 

 solution. 



The precipitate of basic carbonate of copper may be washed by repeated decanta- 

 tion, and thus freed from the sodium sulphate. Remembering that the weight of basic 

 carbonate formed is, approximately, half that of the copper sulphate used, the addition of 

 the required amount of water makes the spraying mixture known as " copper carbonate 

 in suspension," the formula of which, as recommended by Mr. Craig, is : 



Basic carbonate of copper 5 ounces. 



Water 50 gallons. 



It is scarcely necessary to add that the form of copper salt left upon the foliage 

 when dry is the basic carbonate (CuC0 3 , CuOH 2 ). 



Ammoniacal Copper Carbonate. 



This spraying fluid results from the solution in ammonia, of the precipitated basic 

 carbonate of copper, just described, and subsequent dilution with the required amount 

 of water. Two soluble compounds are formed, ammonio-cupric carbonate and ammonio- 

 cupric hydrate, which on drying upon the foliage leave basic carbonate of copper and 

 hydrate of copper, respectively. The formula recommended is : 



Copper carbonate 5 ounces 



Ammonia 2 quarts. 



Water 50 gallons. 



