170 Principles of Plant Culture. 
and water into the copper sulfate solution; stir well, and 
add a few drops of a 20 per cent. solution of potassium fer- 
rocyanid. If a rich, reddish-brown color is produced, add 
more lime. Continue to test and add lime until the reddish- . 
brown color no longer appears. Then add a little more 
lime, as a slight excess of lime is desirable. <A bright, clean 
knife blade may also be used as a test. If a slight film of 
copper forms upon it when placed in the mixture, more lime 
is needed. The Bordeaux mixture is preferably strained 
before use, and should be kept well stirred during its appli- 
cation. It may be applied with any good spray pump. 
The arsenical compounds (28+) may be added to the Bor- 
deaux mixture, and thus a single treatment will serve both 
for insects and fungi. 
330. The Diseases Preventable by Bordeaux Mix- 
ture are the apple and pear scab (328), the downy mildew 
and black rot* of the grape, the early t and late blight f of 
the potato, the gooseberry mildew,? the leaf-blight of the 
pear,|| and some others. 
{n all these diseases, however, the treatment is preventive 
rather than curative. The first application should be made 
before the disease appears, and should be followed occasion- 
ally by others as new foliage is formed, or as the material 
is washed off by rains. 
831. Ammoniacal Solution of Copper Carbonate 
possesses nearly the same fungicidal properties as Bordeaux 
mixture, but adheres less strongly to foliage. Being a solu- 
tion, it requires no straining or stirring, and it leaves a less 
decided stain on drying than the Bordeaux mixture, which 
* Lestadia Bidwellii. + Macrosporium Solan. { Phytophthora infestans. 
2 Spherotheca Mors-uve. | Entomosporium maculatum. 
