11 Aug., 1919. J Copper Fungicides. 485 



talc, kaolin or even plaster of Paris; | lb. of either of these substances 

 to 10 gallons of spray mixture is usually considered sufficient. This 

 addition is more useful in the ca^e of the neutral acetate, the traces left 

 by this salt on the foliage being almost invisible. 



The relative merits and defects of basic and neutral acetate as well 

 as a few practical points in connexion with their use in the vineyard 

 must now be considered. 



Basic Acetate — verdet gris or verdigris.* 



This is the older form; it is sometimes known in France as vert de 

 Montpdlier (Montpellier green) since it was in the vineyards and cellars 

 near that town that the verdegris industry formerly flourished. 



The process of manufacture, though slow, is simple — so much .so that 

 it would be feasible for vinegrowers to manufacture their own verdegris 

 and thus obtain it at a lower cost. 



Sheets of copperf about 4 x 5J inches and weighing about 8 to 10 ozs. 

 alternating with layers of marc are built into a small stack 4 to 6 feet 

 high. The alcohol of the marc becomes oxidised to acetic acid which 

 attacks the copper to form acetate. After five or six days the stack 

 usually presents a whitish, mouldy, appeai'ance; the copper sheets are 

 then removed. On examination numerous small crystals are visible 

 which mainly consist of neutral acetate. The plates held in special 

 racks or frames are next placed in a damp, close, room heated artifically 

 to from 99 degrees to 104 degrees F. The racks, holding about 30 

 sheets each, are dipped rapidly in water every fourth or fifth day. 

 After five or six such immersions the transformation into ba,sic acetate 

 or verdegris is complete; the coating of this substance, which is nearly 

 \ inch thick, is removed by means of a knife and the copper sheets are 

 again treated in a similar manner. 



Two hundred and twenty lbs. of copper yield at each operation, the 

 duration of which is about a month, 33 to 44 lbs. of verdegris. Accord- 

 ing to Camille Saintpierre 3 muids (650 gallons capacity) of marc, yield 

 90 lbs. moist verdegris, which reduces to 59| lbs. commercially dry. or 

 41 lbs. extra dry; 10 lbs. of copper are used up in the process.^ 



Verdegris is very highly spoken of by Viala. Though only briefly 

 mentioned in the first edition of les Maladies de la Vigne (1887) as a 

 promising fungicide, in the third edition (1893) he says — 



The numerous tests of the last few years show clearly and 

 indisputably that solutions of verdet gris constitute one of the most 

 perfect treatments against mildew. The observations of many vine- 

 growers had previously indicated the remarkable adhesive qualities 

 ol verdet gris, qualities which have been scientifically proved by M. 



A. Girard Scalding (of leaves) need never be 



feared .... The spray pumps never become clogged, and 

 there is no need for agitators. On condition that the price of verdet 



• Usually known in England as blue verdegris (it is bluish-green in colour') to distinguish it from green 

 verde'iris, a form manufactured in England by treating copyier plates with pyroligneous acid (acetic acid 

 distilled from wood). According to Thorpe, blue \erde2ris consists mainly of the basic acetate — 



(CH.O ) ,,Cu.,0, 

 whilst areen verdegris has, as principal constituent, the sesqni-basic acetate— 



Cu0..ru. (C..H..O,).,. 



t In order to insure even attack by the acid, these plates are freed from scale, if necessary, rubbed with 

 a solution of verdegris and dried ; unless this precaution be adopted, the first coating produced by the marcs 

 will be black instead of green ! {Thorpe.) 



% See Coste-Floret,^ie« Risidus de la Vendange. 



