382 MOSQUITOES OF NORTH AMERICA 
the Spanish War, and was found to be effective. The price of oil of this kind 
has varied from $2.25 per barrel to $3.00 per barrel, f. o. b., Philadelphia. 
In his early Catskill Mountain experiments one of the writers ascertained 
that about an ounce of kerosene to 15 square feet of surface space is about the 
right proportion, and that such a film would remain persistent for 10 days, or 
slightly longer. He noticed further that even after the iridescent scum had 
apparently disappeared there was still an odor of kerosene about the water and 
that adult mosquitoes avoided it. 
In the work done by Mr. H. J. Quayle, near San Francisco, oiling was 
done upon ponds that could not be drained, upon standing pools remaining 
in creekbeds during the summer, and some was also done on marsh lands. 
The oil used was a combination of heavy oil of 18-degrees gravity and light 
oil of 34-degrees gravity, in the proportion of 4 to 1. This mixture made 
an oil that was just thin enough to spray well from an ordinary spray nozzle, 
and yet was thick enough to withstand very rapid evaporation. It was applied 
by means of a barrel pump where this could be used, but in the creeks and other 
situations, which could not be reached by horse and wagon, the ordinary knap- 
sack pump was used. The price of the heavy oil at Burlingame, California, was 
2 cents a gallon, and of the lighter oil 24 cents a gallon. Mr. Quayle found that 
the duration of efficiency depended somewhat on the nature of the pool and its 
exposure to winds, but in no case could it be counted upon as thoroughly effective 
after a period of four weeks. 
This period of four weeks brings up the question as to the frequency of appli- 
cations of kerosene. The persistence of the oil will undoubtedly vary with the 
temperature and with the character of the pool—whether exposed to the direct 
rays of the sun, shaded by trees, or exposed to the wind. Three weeks will 
probably be the maximum period of efficacy with light fuel oil. The army in 
Cuba renewed the oil every two weeks. 
The application of kerosene to the surface of the water can be made in several 
different ways. If the oil is thin it may be simply poured upon the surface and 
will spread itself. The spraying method, either with the barrel pump, by knap- 
sack pump, or bucket pumps must be used for the heavier oils and where there is 
much aquatic vegetation. One of the writers watched the oiling of ponds with a 
spraying pump in a New Jersey town several years ago. The water treated was 
all in small woodland ponds, and there was necessarily a great waste of kerosene. 
The spray was diffused and became scattered over the vegetation on the borders 
of the pond, a large share of it being wasted in this way, while the shore vegeta- 
tion was killed. On small ponds the oil can be sprinkled to advantage out of an 
ordinary watering pot with a rose nozzle or, for that matter, pouring it out of a 
dipper or cup will be satisfactory. In larger ponds pumps with a straight dis- 
charge nozzle may be used. A straight stream will sink and then rise and spread 
until the whole surface of the pond is covered without waste. The English 
workers in Africa advise mopping the petroleum upon the surface of the water 
by means of cloths tied to the end of a long stick and saturated with kerosene. 
The use of such a mop may be desirable, even where a straight discharge pump 
