standard of living and health, much more basic 
and longer range projects are usually justi- 
fiable. Over a period of years, the public has 
come to realize the necessity of this long- 
range research, and it is being carried out 
extensively in both the universities and the 
U.S, Department of Agriculture, Industry is 
anxious to cooperate in any way possible in 
basic or applied research that enables it to 
advance closer to the common object--that of 
the public good, 
BASIC ENGINEERING RESEARCH 
The primary purpose of basic engineering 
research in pest control is to gaininformation 
on fundamental principles, which is ultimately 
made available to applications research andto 
manufacturers as an aid to the development of 
techniques, equipment requirements, and the 
execution of final designs, For example, U.S, 
Department of Agriculture research studies 
deal with topics of interest in pesticide ap- 
plication ranging from droplet generation, 
counting and sizing, and dispersal through 
particle diffusion in turbulence and the char- 
acterization of particulate deposits on solid 
surfaces. A brief survey of some of the re- 
search studies will be given, with a descrip- 
tion of some special facilities, 
Automatic Scanning 
A flying-spot particle analyzer has recently 
been constructed by Airborne Instruments 
Laboratory, Long Island, N.Y., under contract 
for the Agricultural Engineering Research 
Division of the U.S, Department of Agriculture, 
The instrument is designed to scan negative 
photomicrographs of solid particulates or liquid 
droplets, which are prepared on 35-mm, high- 
contrast film, In addition to the normal func- 
tions of counting and sizing, special logic 
circuits are incorporated in the instrument to 
perform lineal analysis, The measurement 
functions included are (1) size distribution and 
count of intercepts across particles; (2) size 
distribution and count of distances between 
particles; (3) total scan area covered by all 
particles; (4) total scan area represented by 
the space between the particles; and (5) count 
of particles on two boundaries of the scan 
204 
field, The last measurement has statistical 
value in compensation for edge-effect errors 
when a large number of adjacent fields of a 
large area are scanned, 
The particle analyzer sizing calibration is 
fixed with respect to the film, but the cor- 
responding physical particle dimensions being 
dealt with in the measurements are dependent 
only on the microscope magnification used in 
micrograph preparation, The micrographs 
must have the highest possible contrast be- 
tween particle images and the intervening ma- 
trix to insure adequate detectability. Similarly, 
the best possible focus must be maintained 
over the entire area to be scanned onthe micro- 
graphs to insure the greatest possible sizing 
accuracy. Optimum accuracy of the particle 
analyzer is realized for circular particle 
images, although the instrument is designed to 
handle micrographs of irregular particles. 
Several techniques have been used for par= 
ticle and droplet sampling for the particle 
analyzer. Two techniques for collection of 
liquid droplets are (1) use of glossy paper or 
processed photographic paper, as done by 
Fumidge (12), and (2) collection in an im- 
miscible fluid spread on glass microscope 
slides, as discussed by Sharp and Bufton (22), 
Both methods have depended on the use ofa 
dye in the atomized liquid to obtain sufficient 
photographic contrast, The photographic paper 
technique results in very suitable particle 
images and is convenient to use except for the 
disadvantage that spread factors must be deter- 
mined if droplets are to be measured, For 
large droplets, low magnification photography 
or even contact photographic printing of the 
sample paper is adequate, 
By the technique of the immiscible fluid col- 
lection medium, it is possible to capture the 
droplets in spherical, liquid form, and no 
spread factor determinations are necessary, 
The most successful adaptations of this method 
have involved the use of two collection-fluid 
layers, the upper and lower layers less than 
and greater than, respectively, the specific 
gravity of the atomized liquid, With this ar- 
rangement, droplets are trapped at the fluid 
interface, In the case of solid particle sample 
preparation, the work to date has involved 
simply dispersal of solid particles on glass 
microscope slides by standard methods, Nor- 
mally, extra care is givento assurea minimum 
