have been made after spraying with material containing radiosotopes. Fluorescent chemi- 
cals have been used to measure distribution on plants as well as on and under the soil. 
Many of these techniques yield only qualitative or quantitative information, but one should 
not discount techniques because they yield only one kind of information since some 
information is considerably better than no information at all. However, we should not 
be satisfied until we have techniques for making both fast and accurate measurements on 
the plant and in the soil. 
Particle size measurements and particle size distribution description are even 
more difficult and correspondingly little has been done in this field. Most work done on 
this problem has been by direct microscopic particle sizing and counting. This is a tedious 
and expensive procedure and is subject to error as well, both in sizing and in sampling. 
The earliest improvement over this method was developed by Tippler who used nozzles 
being tested to spray molten wax at a temperature which had the correct viscosity and 
surface tension. The spray formed was directed into a cold chamber where it froze and 
was collected. The wax particles formed were then sieved and counted. Elutriation in 
a liquid column, similar to methods used for soil particle analysis, could also be used to 
find particle size distribution. This technique is fast, but has the disadvantage that the 
results with molten wax may not always be comparable with the liquid which will be 
sprayed in practice, and it is of course only a laboratory technique. 
Adler et.al. then developed equipment based on the photoelectric equipment used ina 
wirephoto machine which was in turn adapted to agricultural sprays by English re- 
searchers, Courshee and Trickett. With this equipment a photograph is taken of the 
droplets which have been sampled and the negative is scanned with a spot of light. A 
photocell opposite the light registers electric impulses of various lengths, which size 
and count drops electronically. This information on distribution of chord lengths which 
have been scanned can be converted, using suitable mathematical formulas, into drop 
size distribution. The equipment is limited to measuring drop sizes in any range of l to 
20, but by photographing the droplet sample at various degrees of enlargement a wider 
range of droplet sizes can be recorded. This technique provides information very quickly 
but requires elaborate equipment. To the best of our knowledge, only 5 such installations 
are available in the world today. 
Progress in Deposit Specification. Very little is recorded on research in deposit 
specifications. Work by the USDA during World WarlII indicated that there was an optimum 
size of aerosol for use in some insecticide sprays. Work by the Forest Service indicates 
that certain drop size yield the best results for some type of forest insect spraying work. 
Research at North Carolina, referred to elsewhereinthis paper, showed that by directing 
the spray correctly on tabacco, effective insect control could be obtained with greatly 
reduced dosages. 
Progress on Deposit Control from Ground Equipment. The earliest work in control 
of deposits was in the use of liquidsprays in place of dust. Average particle sizes of dust 
are much smaller than for sprays and have a wider variability in particle distribution 
as well. However, spray did not gain widespread adoption until a development of low 
gallonage, low-pressure sprayers. The next development in deposit control was the use 
of automatic controls to control pressure in spraying equipment. This was followed by 
adjustable spray guns which were used in orchard spraying. Research by Irons on the 
distribution of dust from duster blowers resulted in much improved dust distribution 
from field equipment. In 1948 the work of Barger et al. made possible maximum uniformity 
of spray patterns by correct spray nozzle placement for ground equipment. 
About that same time Lovely and Collins developed photographic techniques to study 
the over-all spray pattern surrounding crops being sprayed, to provide a qualitative trial 
and error method of optimizing spray nozzle placement. In 1956 work by Cox et al. on 
cornborer control equipment resulted in the use of granular insecticide applied above the 
corn to take advantage of the natural funnel of the corn whorls in directing the granular 
insecticide to the point on the corn plant where the insect most frequently fed. This is 
the best specific deposit control which is in use today. 
74 
