31 



results ; with 180 grammes, the pentacupric sulphate S0„, 5CuO; 

 with 202 grammes, the decacupric sulphate SO 2, lOCuO ; with 225 

 grammes the double sulphate of copper and calcium SO 2, 5CuO, CaO. 

 When the quantity of lime is greater than 225 grammes, double sul- 

 phates of copper and calcium are first obtained which are richer in 

 lime than the preceding one, and if the quantity of lime is still further 

 increased up to 4 or 5 kilos, double hydrates of copper and of calcium 

 are obtained. All these compounds contain water in proportions 

 varying with the conditions of preparation, and the major part of 

 them are united to definite proportions of calcic sulphate. Of these 

 compounds, the tetracupric sulphate SO.2, 4CuO, n H^ possesses the 

 highest anticryptogamic value, and in preparing Bordeaux mixture 

 its production should be aimed at, as this yields the largest amount of 

 copper soluble under the action of atmospheric COo or that arising 

 from the life processes of the plants on which the spray is used [see this 

 Review, Ser. A, ii, p. 658]. 



The neutral Bordeaux mixtures which are prepared in the vineyard 

 by adding lime until blue litmus paper ceases to redden, or until red 

 litmus paper begins to turn blue, are mixtures containing a more or 

 less great excess of lime. The so-called acid Bordeaux mixtures 

 produced by adding from 150 to 200 grammes of copper sulphate to 

 the neutral mixtures are, in fact, neutral mixtures with a great excess 

 of lime ; the excess is simply less than that in the mixtures which 

 have been employed in preparing them. 



The neutral Bordeaux mixtures made in the vineyard are composed 

 of calcic sulphate and basic sulphates of copper. The calcic sulphate 

 forms more than one-half of the solid matter in the mixture. The 

 basic sulphates of copper are more particularly : — the decacupric 

 sulphate SO 2, 10 CuO or the double sulphate of copper and calcium 

 SOs, 5 CuO, CaO, for the " neutral " mixtures with a slight excess of 

 lime ; the double sulphate of copper and of calcium SO. 2, 5 CuO, 2 CaO, 

 for the " neutral " mixtures with a high excess of lime. Usually, 

 however, these various basic sulphates of copper are found together 

 in one and the same Bordeaux mixture. 



The Bordeaux mixtures prepared by pouring copper sulphate into 

 milk of lime, are much less dense than those obtained by pouring, as 

 is usual, the lime into the copper sulphate. In either case the same 

 compounds are formed. With ordinary stone lime, it is possible, in 

 practice, to obtain a milk of lime of which the CaO content is easily 

 determinable. In this way titrated milks of lime are obtainable, 

 and with them, it is easy to prepare " neutral " Bordeaux mixtures 

 " without an excess of lime." Their anticryptogamic value is much 

 superior to that of the sprays usually obtained in the vineyard. A 

 small addition of copper sulphate transforms them into (chemically) 

 acid mixtures. In conclusion, it may be said that the quantity of 

 lime necessary to render the copper completely insoluble is much less 

 than that stated by most writers. The neutrality of the mixture does 

 not correspond with the use of a given quantity of lime, but corresponds 

 with the addition of very different quantities of lime, varying as from 

 1 to 1-33. Thus litmus, phenolphthaleine and all other indicators 

 are not accurate. The copper hydrate, which is probably formed 

 when the lime first acts on the copper sulphate, immediately unites with 

 the undecomposed copper sulphate to form basic sulphates of copper. 



