306 
known as a stock solution. In this country Mr. Waite lias used this 
system with great success. His method is described on page 337 of 
this number of the Journal. The advantages of the system are 
obvious; the delay occasioned by having to dissolve small amounts at 
a time is avoided, since a large amount can be dissolved in advance 
and any required number of pounds can be quickly obtained by meas¬ 
uring out the proper number of gallons without any operation of weigh¬ 
ing. If steam is used for dissolving the copper sulphate, exae tly 
the same method may be adopted as when the substance is dissolved 
by suspension. When it is desired to have the solution ready for use 
in a few hours, and neither steam nor hot water is at hand, a stock solu¬ 
tion containing only 1 pound to the gallon can readily be made.* In no 
case should the copper sulphate be dissolved or stored in an iron kettle 
or other metal receptacle, since the copper is thrown down and other 
sulphates formed. A case recently came to my notice where after 
prolonged boiling of the copper sulphate solution in an iron kettle, the 
copper was all thrown down in the form of metallic scales, and the 
liquid on testing proved to be almost pure iron sulphate in solution. 
The solution can be kept a few days or a few weeks in a wooden vessel 
without noticeable change, but probably can not be left indefinitely 
without a slight loss! of strength. The vessel should of course be 
kept covered to prevent evaporation and to keep out impurities. 
SELECTING AND SLAKING THE LIME. 
Only the best well-burnt fresh stone lime should be used in making 
Bordeaux mixture. All powder occurring in the barrel should be 
looked upon with suspicion, since it is very likely to be air-slaked and 
consequently worthless and even dangerous to use for this purpose. 
In slaking, some little care is required in order to get uniformly good 
results. If 50 or 100 pounds are to be slaked, the amount can be 
placed in a barrel or other water-tight vessel. A considerable supply 
of water should be at hand, so that the lime will not get too dry from 
taking up water faster than it can be supplied. At first water should 
be added slowly, stirring vigorously; it should be added just as fast as 
it is taken up by the lime. The lumps of lime should never be allowed 
to project into the air for more than a few seconds. The whole slaking 
mass must be most thoroughly stirred or the lower portions will not be 
wetted at all, the upper layers absorbing all the water. It will not do 
to have just enough water to cause the lumps to swell and fall to a 
In this case instead of weighing out twice as many pounds as the barrel holds 
gallons, the same number of pounds are weighed out and suspended for solution. 
A heu all dissolved, the liquid is brought up to the required amount. This gives a 
solution containing 1 pound to the gallon. 
t According to Clement, as quoted by Biedermann in Ladenburg, Handworterb. d. 
Chemie, 6, 305, a solution of copper sulphate kept in a wooden vessel gradually 
deposits crystalline copper. 
