SOME ASPECTS OF SPRAYING AGAINST PESTS. 
227 
Under " physical means " comes the application of hot water. 
It appears that certain French authors have obtained a measure of 
success in controlling pests of the vine. Experiments were started 
at Long Ashton to see how far this method was applicable as a winter 
treatment. At once difficulties were met with. It was found that in 
order to coagulate the egg contents as high a temperature as 158 0 F. 
was needed. This, of course, is some way below boiling-point, and at 
first sight would appear obtainable in practice. The French authors 
above referred to, however, found that there was a considerable 
reduction of temperature when hot water was sprayed through the 
nozzle of a spraying machine. With the finer nozzles and higher 
pressures the reduction was greatest, though even with coarse nozzles 
using low pressure the drop was considerable. It was found at Long 
Ashton, using a knapsack machine and a coarse nozzle at a distance 
of about 10 inches, that the following fall of temperature occurred : 
Under outdoor conditions, therefore, with possibly a cold wind 
blowing, the outlook did not look hopeful. In addition, the probable 
expense and inconvenience of the method were enough to cause its 
abandonment. There thus remained only chemical means to try. 
As stated previously, chitin is extremely resistant to chemical 
treatment, but it was thought possible that eggs might be attacked 
by such oily bodies as nitrobenzine or paraffin, owing to their 
penetrative power. It was soon found, however, that if used at a 
strength sufficient to kill the eggs extensive damage was done to the 
buds. This treatment, therefore, proved a failure. There are certain 
bodies, namely, hypochlorites, which are used in laboratory practice 
for dissolving chitin in the preparation of insect eggs for microscopic 
examination. In such cases, of course, the solution is concentrated 
and often used hot, being then unsuitable for spraying work. Never- 
theless it was thought possible to adapt the idea, and experiments were 
started with these substances. The most convenient to use on a com- 
mercial scale is bleaching-powder, which is an impure hypochlorite of 
calcium. Eggs were placed in solutions of bleaching-powder, but were 
unaffected by even the strongest solutions. But when the sodium salt 
was used, and especially if caustic soda was present as well, it was 
found possible to attack the chitinous coat. From 10 to 40 minutes 
were required for visible action, the time depending on the strength of 
the solution. 
Even under these conditions of strong solutions the time required was 
relatively long, whereas in practice a spray-fluid will often dry on the 
tree in ten minutes. It was found that if weaker solutions were used, 
such as could be employed on the large scale, as much as three-quarters 
of an hour must be allowed for effective action. This difficulty was 
Temperature of water in machine. 
Issuing water. 
185 0 F. 
1 49 0 F. 
I 3 2°F. 
117 0 F. 
131° F. 
112° F. 
104 0 F. 
94° F- 
