5 6 



Woburn Experimental Fruit Farm, [april, 



fungicide. This is a great disadvantage, but can be obviated 

 by using only just sufficient lime to precipitate all the copper 

 in the first instance, for, in that case, a precipitate is formed 

 which contains none of the basic calcium sulphate. There is, 

 further, a great advantage in thus reducing the lime used, for 

 the basic copper sulphate precipitated is a less basic compound 

 than that in ordinary Bordeaux mixture, and it liberates two 

 and a-half times as much copper sulphate by the subsequent 

 action of the air ; so that a mixture as efficient as the ordinary 

 one may be obtained, with the use of only two-fifths of the 

 quantity of copper sulphate. 



To make this mixture, clear lime-water, instead of milk of 

 lime, must be used ; 6 lb. 6 \ oz. of copper sulphate are dis- 

 solved in water in a wooden pail : and into another large tub 

 of water 2 or 3 lb. of fresh lime are put : after being stirred 

 several times, and allowed to settle, 86 gallons of the clear 

 lime-water are tapped off, and mixed with the copper sulphate, 

 the whole being made up to 100 gallons by the addition of soft 

 water. The mixture must always be tested to make sure that 

 all the copper has been precipitated, and if this is not so, a 

 little more lime-water must be added, and the testing repeated. 

 ' If the liquid gives no red colour with potassium f errocyanide it 

 is in a proper condition for use. The stain produced on a 

 steel knife is often recommended as a test for unprecipitated 

 copper, but it is neither delicate or safe. Any excess of lime 

 added above the minimum required for the complete precipita- 

 tion of the copper weakens the mixture, and represents a direct 

 loss of money. The scorching of foliage sometimes noticed 

 with Bordeaux mixture may be caused by the same substance 

 (the copper sulphate liberated) as that which gives it its fungi- 

 cidal properties, and if so, such scorching is inevitable ; it is 

 certainly a fallacy to suppose that it can be avoided by using 

 excess of lime, indeed, it is very probable that the scorching 

 often observed is due to the large excess of lime used. The 

 mixture made with lime-water as above does not scorch foliage 

 any more than the ordinary mixture, probably less, and has 

 been in constant use in Italy for many years. 



Emulsions. — The investigation into the nature of emulsions 

 has led to the conclusion that emulsification of an oil in water 

 depends on the presence of minute solid particles which arrange 



