520 



beginning of neutralisation than at the end (4 molecules of lime to 

 5 of copper sulphate, as against 9 molecules of lime to 10 of copper 

 sulphate). The proportion of decacupric sulphate is relatively large 

 in this mixture. The value of the mixture is more or less proportional 

 to the quantity of tetracupric sulphate which it contains, as, of all 

 the basic sulphates of copper, this is the one which under the action 

 of the CO 2 of the air will steadily yield the largest proportion of free 

 cupric sulphate. According to the author, the Burgundy mixtures 

 do not contain so large a proportion of basic sulphate owing to the 

 CO 2 set free by the decomposition of the sodium carbonate which 

 they contain ; the acid mixtures contain chiefly the bluish green 

 tetracupric sulphate, which is converted into the blue pentacupric 

 sulphate by excess of sodium carbonate ; sulphates of higher basicity 

 are not formed, because the COo set free by the reaction produces a 

 hydrocarbonate of copper (COg, CuO, 2HoO), which increases in 

 quantity with the cpantity of sodium carbonate in excess. In the 

 positively alkaline Burgundy mixtures, the precipitate chiefly consists 

 of the blue hydrocarbonate, but this is rapidly transformed into the 

 green monohydrated carbonate which is but little soluble in liquids 

 containing COg in solution and is therefore of little value as a 

 fungicide. The supernatant liquids in all cases contain a certain 

 proportion of copper in solution. In the acid Burgundy mixtures this 

 soluble copper exists partly as bicarbonate, which decomposes rapidly 

 when exposed to the air, and by combination with the excess of CUSO4 

 yields an insoluble tetracupric sulphate ; the balance is converted 

 into hydrocarbonate, which is again of small value. In Bordeaux 

 mixtures the fact that the lime used always contains a very appreciable 

 amount of carbonate results in the production of a considerable 

 amount of bicarbonate of copper which, in the acid mixtures, yields 

 tetracupric sulphate ; this will be much less in the neutral mixtures 

 and in the alkaline mixtures. These contain but a small proportion 

 of bicarbonate of copper and this is rapidly converted into hydro- 

 carbonate, the form in which the copper is least active. It would 

 thus appear that the acid mixtures are to be preferred, inasmuch as 

 they contain the largest proportion of tetracupric sulphate. 



Vermorel (V.) & Dantony (E.). Sur la Composition des Bouillies 

 Bordelaises et sur le Cuivre Soluble qu'elles renferment. — [On the 



composition of Bordeaux Mixtures and on the soluble copper they 

 contain.] — Progres Agric. et Vitic, Montpellier, no. 19, 9th May 

 1915, pp. 438-442. 



The authorities who have dealt with this subject are by no means 

 agreed as to the condition in which the insoluble copper exists in 

 Bordeaux mixture, some asserting that it is present as hydrate, and 

 others that the hydrate is associated with various basic sulphates of 

 copper or double sulphates of copper and lime. Nearly all are, however, 

 agreed that only the acid mixtures contain the copper actually in 

 solution. The authors have confined themselves to investigating the 

 commercial products and ordinary water, i.e. to vineyard conditions, 

 and they arrive at the following conclusions : — 



Acid Bordeaux Mixtures- However these are prepared, they contain 

 neither hydrates nor double sulphates, but solely basic sulphates of 



