11 Aug., 1919.] Copper Fungicide,^. 489 



solution dries slowly, and the salt, being soluble, acts corrosively, 

 but neutral verde', owing to loss of acetic acid, changes rapidly into 

 basic verdet, which is insoluble, and therefore incapable of scalding. 

 Now this transformation is very rapid if the spray dries quickly . 

 it is less rapid if it dries slowly. Hence the practical conclusion 

 that neutral verdet slightly burns the leaves only (the bunches are 

 more resistant) if sprayed in moist weather. 



In showerv weather verdet n should therefore prove inferior to 

 other copper mixtures; as a matter of fact, precisely the reverse is 

 the case. Leaves which have been spotted or slightly burnt by 

 verdet sprays are nearly always those which are best protected from 

 mildew.* 



It would thus appear that the prolonged presence on the leaves 



of a concentrated copper solution can better render aseptic, than 

 the necessarily extremely dilute solution resulting from even the 

 most carefully prepared Bordeaux and Burgundy mixtures. 



This is one of the reasons for the superior efficacy of verdel 

 sprays. 



It will be seen from the foregding that the question is a more complex 

 one than might at first sight appear. Both forms of acetate have much 

 to recommend them ; it would seem that if spraying be carried out in 

 fme weather, with a probability of its continuance for a sufficient time 

 to ensure the change to the basic form, that neutral acetate should give 

 excellent results; if, on the other hand, rain is threatening, verdigris is 

 to be preferred. 



Ammona increases the adherence of neutral acetate; the proportion 

 recommended is for each 1 lb. of acetate 1 lb. of liquid ammonia of 

 22° Beaume strength (s.g. -924). In other words, in the case of a 1% 

 spray, 1 lb. of liquid ammonia of above strength to 10 gallons of spray. 



This addition of ammonia has not come into general use, except per- 

 haps in showery weather the advantages gained seem scarcely sufficient 

 ^o justify the extra expense. 



Directions for use. — Dissolve 1 lb. of neutral copper acetate in 10 

 gallons of water; if in fine powder, this may be tipped into the water 

 and stirred until completely dissolved. If in crystals, dissolve 1 lb. in 

 1 or 2 gallons of boiling water, and dilute to 10 gallons. 



To increase spreading power, add 1 oz. of gelatine previously dis- 

 -ol\ed in a little water. 



The addition of talc, kaolin or plaster of Paris at the rate of h lb. 

 tx) 10 gallons of spray mixtiire will insure satisfactory marking of foliage 

 for control purposes. 



Stock solutions may be made by dissolving in hot water, or in col'J 

 water foy suspending the crystals overnight, in a hession bag tied to a 

 stick, so that the crystals are onlv just submerged. 



The strongest stock solution which can be made is at the rate of 

 7 lbs. neatral acetate to 10 gallons water. For use, dilute li srallons t.o 

 10 gallons, with water, adding gelatine and kaolin, &c., as above. 



• This is quite in accord with the view helrl in some quarters, that for a spray to be really effective a 

 -rnall amount of foliase damaae is a necessary evil 



