692 Report oF tHE HORTICULTURIST OF THE 
partly buried in the ground. By keeping the lime covered with 
water it will keep in good condition for an indefinite length of 
time. The copper sulphate may be dissolved in large quantities 
and the proper quantity of this solution may be measured out 
whenever needed. In all except experimental work our plan is 
to dissolve a large quantity of the copper sulphate, using one 
gallon of water for every two pounds of sulphate. Before using 
this solution it is thoroughly stirred each time and then the 
required amount is measured out. Thus if the formula calls for 
four pounds of copper sulphate, two gallons of this solution are 
required. It should never be dissolved or kept in iron vessels, 
since it corrodes the iron. 
Weighing and straining the lime.—It was formerly thought , 
necessary to strain the milk of lime into the copper sulphate 
solution and a coarse sieve or a gunny sack was commonly used 
for this purpose, but it is found except where the nozzles are* not 
directed by, an operator but are stationary, that the operation of 
straining is unnecessary if care is used in pouring. The clear 
lime water is not sufficient but the lime mixed with the water 
must be used. 
The amount of lime necessary to form the Bordeaux mixture 
was formerly determined by weighing, using two-thirds as much 
lime as copper sulphate but by means of the potassium ferro- 
cyanide test the necessity of weighing the lime is now obviated. 
Potassium ferrocyanide test.— Pour the lime into the copper 
sulphate solution, stir the mixture thoroughly and then add a 
drop of the potassium ferrocyanide. If enough lime has been 
added the drop will not change color when it strikes the mixture, 
otherwise it will immediately change to a dark reddish brown 
color. More lime must then be added till the potassium ferro- 
cyanide does not change color when dropped into the mixture. 
The potassium ferrocyanide, also known as the yellow prussiate 
of potash, is a poisonous substance. It is a yellow salt which 
readily dissolves in water and a solution may conveniently be kept 
on hand in a small bottle. The commercial form of the potas- 
sium ferrocyanide may be used. A few cents should purchase 
enough to last through the season. 
Excess of lime.— It is important that enough lime be added, 
otherwise the mixture may injure the foliage, while an excess of 
lime will not harm the foliage. 
