369 
there is still copper in solu tion in the fluid. However, one of the best 
tests for the mixture is simply to notice the color. If too little lime is 
added it turns a greenish blue, if a slight excess is used the color is a 
beautiful sky-blue, and this is the color the mixture should show. If a 
great excess of lime is added the mixture takes on a slightly purplish 
shade of color, especially after standing a few hours. Probably the 
best test for the presence of an excess of lime, even when slight, is to 
ponr some of the mixture into a broad, shallow vessel (a saucer for 
instance), and after a moment or two there will be formed a delicate 
pellicle over the whole surface. This pellicle can readily be seen if the 
dish is held to the light properly. It breaks when stretched and wrin¬ 
kles when compressed. The amount of lime added is also a guide in 
the proper making of the mixture. Theoretically, 1^ pounds of lime are 
required to neutralize (3 pounds of blue sulphate of copper. With ordi¬ 
nary lime, however, this amount is insufficient. Usually it takes twice 
as much to throw down all copper in solution, viz, 2§ pounds. In gen¬ 
eral with good lime it is recommended that 3 pounds be used for every 
6 pounds of sulphate of copper. This strength has been found very 
good for the lemon, which is injured by an excess of copper sulphate 
and also by any considerable excess of lime. It should never take 
more than 4 pounds of lime to neutralize 6 pounds of copper sulphate 
(unless a white or anhydrous copper sulphate has been used). 
To sum up, properly made Bordeaux mixture should show a beauti¬ 
ful sky-blue color, and should form a faint membrane on the surface 
when exposed to the air for a moment in a broad dish. The clear liquid 
obtained on settling should give no brown color with yellow prussiate 
of potash solution, and should give a slightly bluish precipitate with 
copper sulphate solution. To obtain this result about 3 pounds of 
stone lime for every G pounds of copper sulphate should be used. Made 
in this way, the mixture is free from any copper in solution and also 
free from the greenish blue basic compounds, whose action on the plant 
is still in doubt. It contains a slight excess of lime very possibly ben¬ 
eficial to some plants, and certainly less injurious in slight excess than 
would be copper sulphate. 
SHOULD THE MIXTURE BE MADE UP AS NEEDED OR MADE UP MORE 
CONCENTRATED AND DILUTED AFTERWARDS? 
In using stock solutions of copper sulphate and lime, one or both may 
be diluted before they are mixed. I am convinced that it is of great 
advantage to dilute both solutions. In the mixture made from dilute 
solutions the chemical changes necessary to the formation are more 
quickly accomplished, and, best of all, the precipitates formed settle 
much more slowly. Ordinarily I would recommend diluting each con¬ 
stituent to one-half the amount the mixture is to make when completed. 
Then the two dilute solutions, after having been thoroughly stirred, 
