Journal of Agncidturt: , Victoria. [lo Feb., 191 2. 



The kind of soap used is important ; it should be as rich as possible in 

 oleate of soda and free from alkali in excess. Australian soaps, mostly 

 piade from animal fat, would probajbly prove unsuitable for the purpose, 

 since tihey contain much soda stearate. 



Stearate of soda . . . renders the preparation of colloidal copper soap 

 difficult. In a general way, stearate should be proscribed from all insecticide 

 or fungicide formula? containing soap. Our e.xperimetits show that its presence 

 brings about an im])ortant increase in surface tension and a decrease in the solu- 

 bility co-efficient. 



Acetate of Copper or " Verdet." 



Two sorts of acetate of copper have come into prominence of late years 

 for spraying purposes. The.se are the neutral acetate, known in French as 

 verdet iieutre, and what is known as vcrdct gris, which is a mixture of 

 several basic acetates. This substance, of which the English common 

 name is verdigris, has long been used by colour manufacturers, calico 

 dyers, &c. Its mianufacture constituted an important industry 

 in Southerii France manv vears ago, where it was a by-product 

 of wane-making, Ijeing obtained bv treating copper plates with grape- 

 marc which had undergone acetic fertmentation. It is therefore 

 rather curious that it should now turn out to be a valuable specific 

 for the treatment of vine diseases. This use, in fact, appears likely to 

 bring about the revival of the almost extinct verdigris industry. 



Neutral acetate is readily soluble in water; verdet gris, though not 

 soluble, mixes readily with water to form a sort of semi-solution. 



In water, the basic verdets do not give a true solution, such as neutral acetate 

 does. Hydration i)henomena occur; the viscous paste at first formed, if diluted 

 slightly, becomes colloidal. If maceration is sufficiently prolonged and the quantity 

 of water is sufficient, dissociation brings about the separation of a soluble part 

 which colours the solution blue (neutral acetate) and light flakes which float in it, 

 gradually falling tc the bottom, but which the slightest agitation again places in 

 suspension. . . .* 



Both substances constitute excellent fungicides. On the whole, 

 p.eutral verdet is most highly recommended by authorities. Though quite 

 soluble, its adherence is satisfactory, owing to a partial decomposition 

 which takes place after spraying. 



The copper salt' must undergo a chemical change and pass from a soluble to an 

 insoluble colloid state, in order that it may both adhere to the surface and set free 

 a sufficient quantity of copper to contaminate the water drops in which conidia 



and zoospores might (otherwise) germinate With neutral verdet it is an 



insoluble and colloid basic acetate which is s])ontaneously produced after spraying; 

 whereas with dilute liquid mi.xtures of basic verdets, it is a mixture, difficult to 

 define, so far as proportions are concerned, of copper hj-droxide, gelatinous basic 

 acetate and soluble neutral acetate, the latter itself giving rise to the insoluble 

 basic salt (Bencker).* 



Sufficient has been said to show that the verdets should constitute an 

 excellent sprav, insoluble enough to insure adherence, and yet soluble 

 enough to constitute a powerful germicide. These theoretical considera- 

 tions have been am.ply borne out in practice, and the verdets are coming 

 into general use in France. In Switzerland, where downy mildew is 

 particularlv virulent, they are held in high esteem. Either the soluble 

 (neutral), the insoluble (verdet gris), or a mixture of the two are u.sed. 



* A. riejeanne — Les Verdets. Revue de Viticiitture, 3Uth June, lOl*"'. 



* Ibid. 



