250 Report oF THE HORTICULTURAL DEPARTMENT OF THE 
Twenty years of experimentation with copper compounds have 
given us none equal to bordeaux mixture. The value of copper 
as a fungicide was known long before the discovery of this mix- 
ture, but no compound of copper was known before, nor has been 
discovered since, which is so cheap, easily prepared, convenient to 
apply, adhesive to plants, safe to use, and withal so efficient a 
fungicide as bordeaux mixture. 
When properly made, and fresh, bordeaux mixture is light blue, 
robin-egg, or sky-blue, in color. If there be an insufficiency of lime, 
the mixture is greenish-blue; the greater the excess of lime, the 
lighter the color. When exposed to the air for some time it becomes 
a dirty blue-green. Unexposed to the action of the air, bordeaux 
mixture can be held indefinitely without apparent change in chemi- 
cal composition. As a liquid it is thick, but not viscid, though it 
lacks mobility. 
When the ingredients of bordeaux mixture are combined a heavy 
precipitate forms at once. The character of this precipitate depends 
upon the formula used; upon the diluteness of the solutions; the 
character of the lime; the temperature of the solution; and some- 
what upon other minor factors as the kind of water, exposure to 
air, and the quantity of the mixture being made. But the physical 
characters are, in a general way, the same in all mixtures pre- 
pared under normal conditions. Roughly speaking the precipitate 
is a gelatinous mass. Examined under the microscope it is found 
to be somewhat granular and crystalline as well as gelatinous. A 
most important physical character of well-made bordeaux mixture 
is that it is very adhesive. When well dried on sprayed foliage, 
wind does not affect it and only long-continued washing with rain 
removes it. This adhesive property of bordeaux mixture is one 
of its chief points of merit. Sometimes soap, sugar or molasses is 
added to increase this adhesive quality, but these are of doubtful 
value. 
The chemistry of bordeaux mixture, though seemingly simple, 
is somewhat complex. The compounds formed vary greatly, as 
we have seen, with the proportions of the ingredients used and 
with the conditions under which the mixture is made. Since there 
is so much variance in the chemical composition, and since chemists 
who have studied it do not wholly agree, it is of little value to 
go into the details of the various changes thought to take place in 
combining copper sulphate and lime solutions. Only such parts of. 
its chemistry as are well agreed upon need be mentioned here. 
