368 
late, however, the method of Patrigeou,* i. e., adding the milk of lime 
gradually to the copper sulphate until the mixture no longer gives a 
brown precipitate with a solution of the yellow prussiate of potash 
(potassium ferrocyanide). In his bulletin on Bordeaux mixture, soon to 
be issued by this Division, Mr. D. G. Fairchild expresses doubt as to 
the value of this method. As usually recommended, it is certainly not 
by any means an easy method to apply, though it is often assumed to 
be so. If, as is usually the case, there is no means of knowing exactly 
how much lime is added, it is a tedious process to obtain enough with¬ 
out running the risk of using a great excess. As long as the amount 
of lime added is too small the mixture will give on adding a drop of 
potassium ferrocyanide solution a brown reaction plain enough to be 
seen against the greenish blue precipitates, but when nearly all the 
copper sulphate has been neutralized by the lime it is impossible 
to obtain the reaction without waiting for the mixture to settle and 
then testing the clear liquid. Well-made Bordeaux mixture settles 
very slowly and begins to deteriorate as it settles. Moreover, I am con¬ 
vinced that the mixture is not of as good quality when the lime is 
poured in little by little as when the proper amount is added all at 
once. By using the stock milk of lime described above, a definite idea 
is obtained of the*amount of lime that has been added. Moreover, the 
proper ratio, when once carefully determined, can be followed without 
further testing in using up the rest of the two stock solutions tested. 
Lime must be added as long as a brown color is apparent, when a few 
drops of the solution is added to the mixture. A convenient way of 
making the test is to place a column of the mixture several inches 
deep in a small vial and add a few drops of the solution of potassium 
ferrocyanide. 
Unless care be taken to add the milk of lime gradually, there is no 
assurance that there is not a large excess of lime in the Bordeaux mix¬ 
ture as prepared by Patrigeon’s method. However, if the clear liquid 
obtained by letting the mixture settle be tested with a little copper 
sulphate solution, an excess of lime will be shown by a bluish precipi¬ 
tate being formed. If it forms instantly and is very dense, there is a 
large excess of lime, but it it forms only after standing a few minutes 
and is very faint and whitish, there is only a slight excess. If in a 
few moments the clear liquid turns red litmus paper blue, there is an 
excess of lime; if blue litmus paper turns red, there is an excess of cop¬ 
per sulphate present. A simple method of testing for copper sulphate 
(one nearly as sensitive as the potassium ferrocyanide and which can be 
applied without waiting for the liquid to settle) is to immerse the pol¬ 
ished blade of a steel knife in the solution and notice if after a minute 
or two it becomes coated with copper. If it does become so coated 
*Patrigeon, G. Revue Viticole. <^Journ. d’Agr. Prat., 54° aim., t. i., No. 20, May 
15, 1890, pp. 700-704. 
