142 



makes it harder to clog, and the inner box, being removable, can be 

 inverted and washed in a tub of water. Bordeaux mixture, if proper- 

 ly strained, will pass easily through nozzles which throw the finest 

 " misty " spray, while if not properly strained, frequent clogging of 

 the nozzle will result. Where all the fluid has to pass through the 

 minute hole in the circular disc — and owing to the Bordeaux mixture 

 used having been properly strained, have not had to stop once for 

 any blocking of the nozzle. 



If the lime used is freshly burnt (and it must never be forgotten 

 that air-slaked lime is useless for making Bordeaux mixture) and 

 carefully weighed out there is no need to test the mixture before 

 using it. When using " stock solutions," it is a good plan to apply a 

 test at the first mixing. A rough test consists in immersing a clean 

 iron wire of French nail in the Bordeaux mixture for one minute ; 

 if safe to use, the mixture does not affect the nail ; while if unsafe, 

 a copper-plated appearance is given to it. A more delicate and 

 quite simple test is as follows : — Procure from a chemist a 10 per cent, 

 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,t Bordeaux mixture made from these proprietary 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 of opinion that in practical spraying dried 

 Bordeaux mixture is less efficient than the ordinary mixture. As 

 long ago as 1900, Mr. R. U. Moss pointed out t how thoroughly 



See Pickering, in Jour. Afiric. Science, iii (1909). 

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

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



