492 INSECT AND FUNGOUS ENEMIES OF THE APPLE. 
the spray nozzles, and it is a good practice to strain the stock solu- 
tion of lime while pouring it into the dilution tank. The best mate- 
rial for a strainer is brass wire netting of about 20 meshes to the inch. 
ARSENATE OF LEAD AND OTHER ARSENICALS. 
Arsenate of lead is the principal arsenical used in orchard spray- 
ing. It comes on the market in a puttylike paste and to a more 
limited extent in the form of a powder. Its present large use is due 
to certain advantages it has over other arsenicals, in that it contains 
very little water-soluble arsenic, and is therefore much less likely to 
injure the foliage. It also adheres better than other arsenicals, such 
as Paris green and arsenite of lime. All arsenicals used in spraying 
fruit trees may be used in Bordeaux mixture. However, not all of 
these can be used in lime-sulphur solutions without danger of foliage 
injury. Arsenate of lead when added to lime-sulphur solution under- 
goes considerable chemical alterations, as shown by the prompt 
change in color of the mixture. Chemical analyses show that a small 
percentage of the arsenate of lead is broken down, and lead sulphid 
and arsenate of lime formed. Abundant experience, however, has 
shown that this alteration of the chemical nature of the arsenical 
and of the lime-sulphur wash does not injuriously affect their effi- 
ciency as fungicides and insecticides, nor materially add to the danger 
of foliage or fruit injury. Arsenate of lead is used in Bordeaux | 
mixture or lime-sulphur at the rate of 2 pounds to each 50 gallons 
of the spray. As there are numerous brands of arsenate of lead 
upon the market the grower should be careful to purchase from re- 
liable firms. When the paste form of arsenate of lead is used it must 
be worked free in water before it is added to the spray. Powdered 
arsenate of lead is used at about one-half the strength of the paste 
form. . 
In large spraying operations it will be more convenient to pre- 
pare in advance a stock mixture of arsenate of lead as follows: Place 
100 pounds of arsenate of lead in a barrel, with sufficient water to 
work into a thin paste, diluting finally with water to exactly 25 gal- 
lons. When thoroughly stirred each gallon of the stock solution will 
thus contain 4 pounds of arsenate of lead, the amount necessary for 
100 gallons of spray. In smaller spraying operations the proper 
quantity of arsenate of lead may be weighed out as needed and 
thinned with water. In all cases the arsenate of lead should be 
strained before or as it is poured into the spray tank. The neces- 
sary care should be exercised to keep the poison out of the reach 
cf domestic and other animals. 
492 
