INSECTICIDES, FUNGICIDES, ETC. 185 



total leaf surface affected, was practically the same as that 

 caused by the Burgundy mixture (XI, 145) 



By-products of Burgundy 

 Burgundy Mixture. * 



tre - Sod. Sulph. Sod. bicarb. Both. 

 Scorching 64 37 42 60 



Other experiments supported the view that it was the by- 

 products which were mainly responsible for the damage, and 

 previous work had shown that similar salts, such as sodium 

 chloride, would in many cases produce serious scorching (VIII, 

 106). The effect, however, was subject to much greater varia- 

 tion when the material was sprayed on to the leaves, instead of 

 the leaves being immersed in the solution , the explanation of this 

 being very simple ; for when a solution containing a highly 

 soluble salt such as sodium sulphate is sprayed on to a plant, 

 the drops, whatever the proportion of substance contained in 

 them, will become concentrated to the maximum before they dry 

 up, and intense, but local, action will result, very much modified, 

 however, by the condition of the weather, the size of the drops, 

 etc. One great advantage presented by Bordeaux mixture 

 over Burgundy mixture is that the by-product in the former 

 case calcium sulphate is very sparingty soluble, dissolving 

 to the extent of only 0-25 per cent., and it exercises, therefore, 

 no appreciable scorching action on foliage. 



Like Bordeaux mixture, Burgundy mixture changes after a 

 time, the copper carbonate present becoming converted into 

 another carbonate, malachite, which forms as minute, spherical 

 particles, settling very rapidly in the liquid, and rendering the 

 mixture quite unsuitable for spraying purposes. The change, 

 which generally occurs suddenly, does not take place for some 

 days if the mixture is left at rest, the time elapsing under various 

 conditions being recorded on p. 184 ; but when the mixture 

 is agitated, it may take place within a few hours. The same 

 change must always occur sooner or later to the deposit of 

 material sprayed on to the leaves, and the solubility of malachite 

 in water must give the measure of the strength of copper solution 

 which after a time will be in contact with the leaf. This solu- 

 bility is from 0-00008 per cent, of copper in pure water, to 0-006 

 per cent, in water saturated with carbonic acid. 



