228 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



Stirring the latter energetically. Theoretically 14 lb. of pure quick- 

 lime suffice to precipitate 624 lb. of pure blue vitriol. Practically the 

 amount of lime used is always greater, because the lime is never pure. 

 The amount of lime varies, therefore, according to its purity, from 1-3 

 lb. of lime to 3 lb. of blue vitriol. The most advisable quantities to- 

 form an active bouillie are 10 lb. of blue vitriol in 50 gallons of water, 

 and 3^-10 lb. of lime, dissolved in 50 gallons of water. The mixture 

 formed by these two solutions is termed a 1 per cent solution. 



Properties of Copper Hydrate. — Copper hydrate is a pale blue 

 precipitate, which is more fine and gelatinous the lower the temperature 

 at which it is precipitated. It is almost insoluble in water at all 

 temperatures ; it is converted in hot water into black copper oxide, CuO. 

 It is, however, soluble in mineral and organic acids. 



Properties of Bouillies Bordelaises. — A bouillie bordelaise, 

 prepared in good condition, should have the following properties r 

 It should be neutral or slightly alkaline ; it must never contain an 

 excess of blue vitriol. To ascertain its composition a little of the 

 bouillie is filtered, or allowed to settle. The limpid liquid collected 

 should not be tinted blue (which would point to unchanged blue 

 vitriol), but should be absolutely colourless. It should give no reaction 

 with litmus paper, nor an alkaline reaction with turmeric paper. 

 Another and still better method of showing the presence of small 

 quantities of undecomposed blue vitriol consists in placing a little 

 bouillie bordelaise in a saucer and to pour on it a few drops of yellow 

 prussiate. The presence of blue vitriol is revealed by a red coloration 

 of the bouillie. A blade of a knife dipped in a bouillie, still containing 

 blue vitriol, is covered with a deposit of metallic copper. 



The bouillie must be tested and respond to the tests in the right 

 loay, otherivise it is itnfit for all the ptuyoses for lohich it is intended. 



Too often the sprayings eventually burn the leaves and the young 

 parts of the plant. They are due, with few exceptions, to faults in 

 the composition of the bouillie. Traces of blue vitriol, not converted 

 into cupric hydrate, suffice to cause these burns. As a preventive of 

 cryptogamic diseases the bouillie must be as adherent as possible, so 

 as to prolong its action on the surface of the vulnerable organs of the 

 plant. 



Adhesion depends on several factors: (1) The blue vitriol should 

 be precipitated cold, as above described, by milk of lime. (2) The 

 more pure (fatty) the lime, the more adherent the bouillie. (3) The 

 more freshly prepared, the more adherent the bouillie. (4) The bouillie 

 is the more adherent the more nearly neutral it is ; that is, without an 

 excess of lime. Although it is not injurious to vegetation, it is well' 

 to estimate exactly the quantity of lime to use in preparing the bouillie. 

 Lime in excess has, moreover, the drawback of retarding the action of the 

 bouillie bordelaise on the germs of cryptogamic fungi. Cupric hydrate 

 as deposited on the leaf of a plant is, so to speak, insoluble, and thus- 

 inert towards the spores in contact with it. To become active it must. 

 be converted, in contact (1) with the air, into copper carbonate, soluble 

 at the rate of 40 milligrammes in a litre of water containing carbonic 

 acid ; or (2) with carbonate of ammonia, or be dissolved by the juice 



