8oo 



Bordeaux Mixture. 



[JAN, 



solution of ferrocyanide of potassium (which is a poison) and 

 pour a little of this into a white saucer ; then drop a few drops 

 of the Bordeaux mixture into the ferrocyanide of potassium. 

 No change of colour occurs if the mixture is safe to use, 

 while a cloudy reddish-brown discoloration (very easy to 

 see) occurs immediately if the mixture is unsafe to use. An 

 unsafe mixture can be made safe by adding more "milk-of- 

 lime " until it passes the test. 



In spraying fruit trees (and also potatoes) there is no need 

 whatever to add anything to the Bordeaux mixture with the 

 object of making it adhere better; soap is quite unnecessary 

 and should never be used, and treacle is useless.* The nature 

 of the precipitate which constitutes Bordeaux mixture causes 

 it, when applied in a " misty" spray (see below), to adhere 

 most intimately to the part sprayed. 



Ready-made Bordeaux mixture is at present put on the 

 market in powder form, and as a paste. The best results, 

 however, in my experience, are only obtained when 

 Bordeaux mixture is home-made and freshly-mixed. As 

 regards the numerous proprietary Bordeaux mixtures put up 

 in powder form, the fruit-grower must be warned against 

 using these. Such preparations are made by mixing lime and 

 copper sulphate in concentrated form, and then drying and 

 grinding the product. As Mr. S. U. Pickering has 

 lately pointed out,f Bordeaux mixture made from these pro- 

 prietary powders settles at least ten times more rapidly than 

 the freshly-prepared mixture; consequently it is a very 

 inefficient spraying material. There is a general consensus oi 

 opinion that in practical spraying dried Bordeaux mixture is 

 less efficient that the ordinary mixture. As long ago 

 as 1900, Mr. R. U. Moss pointed outj how thoroughly inferior 

 such ready-made Bordeaux mixtures are to the home-made 

 freshly-mixed article. One of the best known of these mix- 

 tures sold in powder form was tested in two ways. In the first 

 experiment the powder after being mixed with water accord- 

 ing to the directions was thoroughly shaken up in a glass 

 cylinder, and then allowed to stand for five minutes. It was 



* See Pickering, in Jour. Agric. Science, iii (1909). 



f Jour. Agric. Science, iii, 170 (1909). 



% Econ. Proc. Royal Dublin Soc, vol. i, part iii, p. 109. 



