New YorK AGRIGULTURAL HXPERIMENT STATION. 251 
began to drip slightly. By so doing all of the emulsion that 
would adhere was applied to each tree. It is apparent that if 
less were applied it would be very difficult to tell whether the 
work had been thorough or not. On the other hand prolonged 
spraying and consequent over drenching would be merely a 
waste of material and would have practically no effect upon the 
quantity of petroleum that finally clings to the tree because the 
excess of emulsion does not adhere to it. Also if the machine 
emulsifies the oil and water as thoroughly as in our own experi- 
ence there will be no danger from free oil as the excess of emul- 
sion will drain off before separation can take place. Hence a 
tree sprayed to a moderate excess with an emulsion containing 
say 25 per ct. of petroleum would finally retain no more petro- 
leum than if sprayed merely to the dripping point. If, there- 
fore, the spray is directed upon each tree until its full capacity 
to hold the emulsion is reached, that is until it begins to drip, 
an amount of oil in proportion to the percentage indicated is 
practically maintained. However, it is to be noted that in the 
case of unusually rough or cracked bark or open wounds that 
would hold the emulsion the accumulation of oil may cause 
injury. It is also possible that, in case of over drenching, the oil 
that would soak into the ground might cause injury to the roots. 
CHARACTER OF CRUDE PETROLEUM. 
Crude petroleum is an oily, inflammable liquid varying in color 
from very dark brown to greenish tints. By refining it yields 
a number of valuable products including paraffin, lubricating 
and illuminating oils and a series of highly volatile oils. It is 
the heavier oils that make it especially valuable as an insecti- 
cide. Crude petroleum varies in appearance and composition 
according to the locality from which it was taken. The eastern 
oils are said to vary greatly from the western and most foreign 
oils, the former having a paraffin and the latter an asphalt 
base. The true indication of the safety of petroleum as an 
insecticide evidently depends upon its specific gravity; as it has 
been found that petroleum having a specific gravity of 43° or 
