XVII. MISCELLANEOUS PKODUCTS USED IN AGRICULTURE 365 



while in the usual Bordeaux mixture, the precipitate, approximating in 

 composition to 10CuO.SO a , 4CaO.SO 3 , could only yield one-tenth of 

 its copper as copper sulphate, and this liberation of copper sulphate- 

 would probably only begin after the basic calcium sulphate had beea 

 acted upon by carbon dioxide. 



In order to prepare Bordeaux mixture containing 4CuO.S0 3 , 

 Pickering recommends that one gramme of crystallised copper sulphate 

 in solution be precipitated by the addition of 134 c.c. of saturated lime- 

 water, and points out that such a preparation is rather more effective 

 than normal Bordeaux mixture made by precipitating more than double 

 the quantity of copper sulphate by excess of milk of lime. 



On a practical scale, the mixture could be prepared by dissolving 

 1 Ib. of crystallised copper sulphate in -J to 1 gallon of water and then 

 ad ling 13^ gallons of clear, saturated lime water. After thorough 

 mixing, the liquid should be tested for soluble copper salts by filtering 

 a portion and adding a solution of potassium ferrocyanide. If a red. 

 colouration be obtained, further addition of lime water should be made, 

 or the mixture would have a corrosive action on the foliage. 



This new method of preparation would seem to possess several ad- 

 vantages, in efficacy of the product, freedom from tendency to choke 

 the spraying nozzles, etc., but considerable care is necessary. Unless 

 the lime water be really saturated, there is danger of leaving excess of 

 copper sulphate in the final liquid, and this, of course, would be in- 

 jurious to the foliage. 



According to a recent paper by Barker- and Gimingham l however,, 

 the fungicidal action oi' Bordeaux mixture is due to the direct action 

 of the solid copper compounds upon the hyphce of the fungus on the 

 surface of the leaf and not to any liberation of soluble copper com- 

 pounds by the action of carbon dioxide on the precipitated basic 

 salts. 



Other copper compounds used as fungicides are 



1. " Eau celeste" which is essentially ammonio-copper sulphate, 

 CuSO 4 .4NH 3 .H 2 O, the well-known magnificent blue solution, formed 

 when ammonia is added in excess to a solution of copper sulphate. 

 The usual proportions are about 5 Ib. blue vitriol and 6 or 7 pints of 

 strong ammonia in 100 gallons of water. 



2. Ammoniacal copper carbonate, made by dissolving copper car- 

 bonate in ammonia or ammonium carbonate solution. Quantities often 

 used are copper carbonate 10 ounces, strong ammonia 6 pints, water 

 100 gallons. 



3. Copper sulphate and sulphur powder. A mixture of equal 

 weights of powdered blue vitriol and air-slaked lime is mixed with 20 

 times its weight of powdered sulphur. 



Copper sulphate and ammonio-copper sulphate also find a limited 

 application in veterinary practice as astringents. 



Copper sulphate is also used as a disinfectant in France, a 5 per cent 

 solution being recommended. It has been employed as a disinfectant, 

 for cow-sheds after rinderpest, but is expensive. 



1 Jour. Agric. Sci., 1911, 76. 



