11 Aug., 1919.] Copper Fi(ngicides. 487 



mixtui-e. Gelatine solution being very liable to putrefaction, it is well 

 to add a small quantity of the verdegiis stock mixture : say half a pint 

 to 1 gallon. 



Neutkal or Normal Copper Acetate Cu (CoHjO,),. HoO. 



This crystalline salt is of more recent introduction for spraying pur- 

 poses than verdegris ; It is easily prepared from the latter by dissolving 

 it in dilute acetic acid, evaporating and crystallising out, though there 

 are other methods of preparation. 



Being entirely soluble in water, the spray mixture can be pre- 

 pared at once : as soon as dissolved it is ready for use, preliminary 

 soak.ng for a couple of days, such as is required for verdegris, is no 

 longer necessary. It is harmless to foliage at the spraying strengtli 

 generally used, though it is probably rather more conducive to scalding 

 than verdegris, especially in moist weather. Being applied in the shape 

 of a clear solution, it ensures absolute freedom from clogging of nozzles. 



It IS soluble in thirteen parts of cold and five parts of hot water; 

 the strongest solution would thus contain 7 per cent, of the salt., A 

 stronger solution could be made with hot water, but part of the acetate 

 would crystallise out on cooling. 



In vine-growing practice, neutral acetate has latterly become very 

 popular, as Chuard and Porcliet pointed out — * 



Of recent years there has been a tendency, in various vine- 

 growing regions, to substitute a 1 per cent, solution of neutral 



copper acetate for the usual copper spray mixtures 



Being readily soluble in water, and inoffensive for the vine foliage 



at the usual strengths of from ^ to 1^ per cent., neutral verdet is 



of very convenient application, and in the numerous field trials we 



have been able to check, it has proved itself at least as effective as 



lime or soda houiUies (copper mixtures). 



Though completely soluble itself, the residue left by a spray applica- 



catlon on the vine tissues soon undergoes change, passing from a soluble 



to an insoluble colloid (non-crystalline) form, practically identical with 



the residue left by a verdegris spray mixture; removal iDy rain, such a^ 



might logically be expected with an entirely soluble substance, need not 



therefore be feared — 



With neutral verdet it is an insoluble and colloid basic acetate, 

 which is spontaneously produced after spraying ; whereas with 

 dilute mixtures of basic verdeis (verdeyr/.s), it is a mixture, difficult 

 to define so far as proportions are concerned, of copper hydroxide, 

 gelatinous basic acetate, and soluble neutral acetate; the latter 

 ultimately giving rise to the insoluble basic salt (Bencker)f . 



The time which must elapse before this transfonnation is complete, 

 in other words, before the deposit loses solubility to a sufficient extent 

 to afford lasting protection, and to resist washing off by rain, is a poini 

 of considerab'e importance, especially in a wet spring, and one concerning 

 which the opinion of Chuard and Porchet may again be quoted| — 



Owing to its ready solubility, the question arises whether rain 

 water does not soon remove the residue left by a spraying with 



* Compte!<-rendm de V Acndhnie des Sciences (Paris) WIS. 



t A Dejeanne — ] es Verdets Revue de Viticulture, 30th June, 1910. 



J Compies — Rend us 1905. 



