Letters on the Diseases of Plants. 53 



The advantages of this method of preparing the mixture are — 



1. Expedition. It is the quickest way where the mixture is regularly 



used and is required from time to time through the season. 



2. It is accurate. It does away with the uncei'tainty always connected 



with the strength of commercial quicklime. 



3. It is the most economical way. No lime is wasted. 



4. The resulting mixture will ahoays he tJie same, and there will be no 



risk of " burning " the plants by spraying with a mixture too strong, 

 or wasting time applying a mixture that is too weak to do any 

 good. Both these mistakes are too common, and will account for 

 the failures that are from time to time reported to me. Bear in 

 mind that there is no doubt about the efficacy of this mixture in the 

 cases where properly qualified persons recommend it. All the 

 failures, and I am glad to say they are comparatively few, arise 

 from ignorance of how to make or apply the mixture. 



5. Finally, the making of the mixture from dilute solutions gives a finer 



precipitate, which is more easily kept in suspension, and is less 

 liable to cloy the nozzle. Perhaps this ought to be made a little 

 plainer. I will therefore put it this way : If 1 lb. of sulphate of 

 copper dissolved in ten gallons of water be neutralised by 1 lb. 

 of quicklime in ten gallons of water, the precipitate will he finer 

 than if 1 lb. of sulphate of copper dissolved in one gallon of water 

 be neutralised with 1 lb. of quicklime dissolved in one gallon of 

 water, — even though afterwards the latter mixture be made up 

 to 20 gallons, which is the same bulk as the first when finished ; 

 and, of course, if the precipitate is finer it will gi-ve correspondingly 

 less difficulty in the application. 



2. Compound Mixtures. 



I now come to the question of mixing two of the different liquids used 

 to combat insects and fungi. This is a matter that brings letters of inquiry 

 from time to time. Suppose, for instance, there is no chemical reason why 

 Bordeaux mixture, a fungicide, and the resin-soda compound, an insecticide, 

 may not be mixed. Suppose, as is actually the case, that when those two 

 liquids are mixed, each retains all its chemical properties, would it not be a 

 saving to mix the two and apply both at once, and thus with one cottp attack 

 both insect and fungus pests? This is the question that has been pro- 

 pounded to me more than once, and has cropped up also in other parts of 

 the world. This particular question, put by an inquirer, has been answered 

 as follows : — 



" You are quite right as to the weakening of each mixture by the other, 

 which could, however, be compensated for by doubling the strength of each. 

 The advisability or otherwise of using the two mixtures together is not yet 

 fully settled by experimenters. To me the probability in this particular 

 case (Bordeaux and resin-soda) seems to be that experiment will show the 

 mixture to be inadvisable, (I) because the Bordeaux will "be clotted into a 

 more insoluble state by the resin compound, and (2) because the resin 

 compound (which, as you know, acts partly by" sealing in " the scales and 

 thus smothering them) will be converted into a less perfect varnish by the 

 lime and copper compounds. Two separate sprayings, on the other hand, 

 even supposing them to be different mixtures, will be high in effectiveness 



