596 Journal of Agriculture, Victoria. [10 Oct., 1918. 



though perhaps more active at first, it is removed by heavy rain sooner 

 than the precipitate of ordinary Bordeaux, thus rendering the duration 

 of its protection insufficient. 



Bordeaux Mixture may thus be acid, neutral, or alkaline. Copper 

 sulphate is an acid salt. Its acidity may be neutralized by various 

 substances ; in the case of " Bordeaux " lime is the alkali used. If 

 chemically pure quicklime (slaked and made into a milk with water) 

 be progressively added to a solution of copper sulphate it will be found 

 that if 10 pounds of copper sulphate are present in the solution this 

 will maintain its acid reaction until 1.685 lbs. of lime have been added. 

 At this point the mixture becomes neutral. If the addition of lime be 

 continued, it will not be until the total quantity of pure lime reaches 

 2.25 lbs. that the mixture shows an alkaline reaction. It is thus evi- 

 dent that a neutral mixture is obtained by using quantities of lime vary- 

 ing between tihese two limits. It is really the nature of the precipitate 

 which differs; the nearer the quajitity of lime used approaches to the 

 figure 2.25 lbs. the greater the basicity of the precipitate. If more 

 than 2.25 lbs. of lime are employed an alkaline " Bordeaux " will be 

 obtained. 



It is thus evident that the standard Bordeaux Mixture used in France, 

 viz., half as much quicklime as bluestone, must, with lime of anything 

 like good quality, always result in an alkaline mixture. Even when 

 the quantity of lime is gauged by test paper instead of by weighing, the 

 resulting mixture will inevitably be alkaline, for the reason that milk 

 of lime is a mixture of solid particles with water, and not a true solu- 

 tion. Even with thorough stirring the action of the lime takes trme; 

 each minute grain becomes surrounded by a vesicle or bladder of basic 

 copper sulphates, lime sulphate, &c., with a result that the lime con- 

 tinues its action for some considerable time after the test paper indi- 

 cates the first signs of alkalinity. Even if slightly acid when first 

 prepared " Bordeaux " usually becomes distinctly alkaline later on 

 owing to the neutralizing action continuing. 



Physical Nature of the Precipitate. 



This is probably of equal importance to the chemical composition, 

 since it has an important bearing on the adherence of the " Bordeaux," 

 w'hich varies very considerably according to the mode of preparation. 

 It is for this reason that it is so important that the line should be poured 

 into the copper sulphate solution, and not the copper into the lime milk. 

 In the former case the vesicles mentioned above are a characteristic 

 feature of the precipitate ; in the latter case they do not occur — the pre- 

 cipitate, though light, is granular, and on drying is much less adherent 

 to the green tissues of the vine. 



The Galloway or American method of preparing " Bordeaux," in very 

 general use by Victorian orchardists, certainly gives a mixture of very 

 high quality, with a fine, light precipitate which adheres well. It con- 

 sists in making a dilute solution of sulphate of copper and a dilute milk 

 of lime. These two are intimately mixed by running them separately in 

 equal quantities at a time into a third vessel. The main feature of the 

 method is that dilute solutions are made to react on one another; the 



