4S6 J oil null of Agriculture, Victoria. 1 11 Aug., 1919. 



should remain cheap we consider that solutions of this substanro 

 constitute one of the most perfect treatments against mildew. 

 Professor Ravaz also speaks favorably of verdigris, as will be seen by 

 tho following extract from Le Mildiow, page 129 — 



Verdet gris is a complex sub3tauce, it contains mainly bi-basic 

 copper acetate and some other acetates. Thoiigh its composition 

 is not constant, basic acetate Cu (C^IT-.O^,)^ CuH^.O. predominates. 

 It occurs in small lumps or cones of a blue gray colour containing 

 33 to 35 per cent, of copper. In water it breaks ujj — ■ 



1 . Into neutral acetate Cu (C2H302)2H20 which dissolves in the 



water. 



2. Into hydrated copper oxide, according to M. G. Bencker, or 



into tri-basic acetate according to other chemists, spai- 

 ingly soluble substances which are precipitated or 

 crystallised. It is ahnost certain that some substances 

 other than hydrated oxide are produced. 

 At any rate this mixture supplies dissolved copper just as neutral 

 acetate does, which acts immediately on the germs of the parasite, 

 and slightly soluble precipitated copper, which constitutes the ])erma- 

 nent reserve. Verdcf gris should thus be very effective, and it h?s 

 everywhere given good results." 

 The following extract''' will give some further idea of what ha})pens 

 when verdegris is mixed with water — 



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

 neutral acetate does. Hydration phenomena occur; the viscous 

 paste at first formed, if diluted slightly, becomes colloidal. If mace- 

 ration' is sufficiently prolonged and the quantity of water is 

 sufficient, dissociation brings about the separation of a soluble 

 part M'hich colours the solution blue (neutral acfetate) and light 

 flakes which float in it, gradually falling to the bottom but which 



the sl-ghtest agitation again places in suspension 



It is this extreme lightness of the sediment) which insures the great 

 freedom from nozzle troiibles characteristic of verdegris mixtures which 

 may indeed almost be looked upon as semi-solutions; nevertheless, in 

 order to obtain the best result, attention must be paid to one pointr— it is 

 necessary to soak the verdegris in water for a few days before making 

 up the spray mixtiire. 



If verdegris has not been soaked long enough the resulting mixture 

 will be lumpy, it will adhere badlv and lose much of its efficacy .f 



Directions for mixing. — Quantity required, 1 lb. for every iO gallons 

 of water. Soak the 1 lb. of verdegris in 1 gallon of water for 2 or 3 

 days with occasional stirring; before use, dilute to 10 gallons of water. 

 Should it be desired to increase the spreading power add 1 oz. of 

 gelatine dissolved in a little water. The gelatine should be soaked in 

 enough water to merely cover it, for a few hours, on adding about two 

 or three times the bulk of boiling water it will immediately dissolve. 



A stock mixture can with advantage be made at the rate of 10 lb. 

 verdegris to 10 gallons water, 1 gallon of which, taken after thorough 

 Stirling, would be sufficient to dilute to 10 gallons of spray mixture. 



A stock solution of gelatine may likewise be made, at the rate of 

 4 ozs. per gallon — 1 quar t of this will suffice for 10 gallons of spray 



* A. Dejeanne — l es Verdets Heviie de Vitindture. 30th .Tune, 1910. 

 t Kavaz : le Mildion, p.-»ge 130. 



