11] Potato Disease and Allied Diseases 27 
powdered state). Tie the copper sulphate in a cotton 
bag or a piece of sacking, and suspend it so that it 
reaches just below the surface of the water in the tub. 
Now carefully pick over the lime, throwing out any 
pieces that are overburnt, and weigh out 4 Ibs. of it. 
Put this into the wooden pail and slake it with about 
a quart of water which should be added very slowly. 
Covering the bucket with a piece of sacking helps the 
lime to slake. When the lime has crumbled add about 
another quart of water and work the lime into a stiff 
paste; add more water and stir to make a creamy 
liquid. Now put 20 gallons of water into the small 
tub, pour the creamy liquid into it through a fine 
sieve or a piece of coarse sacking, and add water until 
the tub contains 25 gallons. 
When the blue stone in the large tub has all dis- 
solved slowly pour the lime solution into it, stir well 
meanwhile and continue to do so for some time. If 
the above operations have been carefully carried out 
the mixture should consist of a light blue precipitate 
suspended in a colourless solution. A granular pre- 
cipitate which sinks quickly to the bottom shows the 
mixture to be a poor one. It should remain floating 
for some time. In some cases Bordeaux mixture 
damages the potato plant. This is usually due to 
some error in making and is caused by the presence 
of free copper sulphate. It is a simple matter to test 
the safety of the mixture. If a knife blade becomes 
coated with copper when placed in the liquid, it is 
unsafe and more lime solution should be added. 
A better test is to add a few drops of the mixture 
to a solution of potassium ferrocyanide on a piece of 
white porcelain. If a brownish colour is produced 
