الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 16 |  |  |
| | | from | 16 | | |
Abstract
In recent years, many researchers have put much effort into devefoping new chemicals for use as insecticide and herbicides. The use of herbicides to control and inhibit undesirable weed growth is well known and accepted. As a result, there is widespread use in agricultural, industrial, and domestic fields. Roadsides, embankments, railway rights¬of way and other earth surfaces are often subjected to treatment with toxic chemicals, organic and inorganic. Numerous compounds with widely variant functionalities are effective to a greater or lesser degree in inhibiting or destroying the growth of undesirable vegetation. One of the most widely used techniques in chemical application is to accomplish the control by spraying the active chemical upon the area within which the disease or the weed is expected. In some instances, expected areas of weed growth are sprayed in early spring or late fall to prevent an appearance of noxious plants or at least to severely weaken their
growth patterns. Certain problems arise in connection with such chemical applicatipns. First, and foremost, is a problem of misting or fogging which generally begins to occur at a spray pressure of 15 psi and worsens as spray pressures are increased. The chemical spray tends to drift and valuable crops that are downwind can be destroyed or damaged to
varying degrees. In some instances, due to the extreme toxicity of certain chemicals, even valuable animal life such as livestock can be injured. The problem of drift has become more widespread in recent years, due to the more extensive use of herbicides and to the application of
the chemical materials as concentrated solutions in low volumes per acre. Generally, undesirable drift from the spraying of the chemical materials may occur 1n two ways. First, spray drift occurs as a result of the smaller droplets in the spray being car”ried away from the target by wind or convection currents. Second, the vapor from d volatile chemical may be carried away from the target area during or after the spraying in a type of phenomenon called vapor drifto This is most likely to occur in hot weather and can take place even in the absence of wind. Efforts to substantially reduce spray and vapor drift have in the past generally
been unsuccessful or impractical. To minimize drift, spraying may be carried out only on days when there is negligible air movement. Such a practice is impractical and substantially inhibits overall efficiency of the spraying program. Likewise, efforts to reduce undesirable misting
or fogging by specific design of spray nozzles have met with only limited success, and in such cases have required an impractical sophisticated mechanical design. Lowering the spray pressure does aid to some degree in preventing drift. However, the need for good coverage and uniform distribution in obtaining good control does not allow much reduction in spray pressureo
One of the most successful ways to control drift is to minimize the number of the fine drops in the spray produced. Fine drops are produced during the liquid disintegration due to the interaction between the spray fluid and the surrounding gas. The properties of the spray fluid and the surrounding air are the main factors which speed or delay the disintegration process, For instance, by increasing the liquid viscosity the resistance
of the spray sheet to breakup into drops increases and consequently the spray spectrum shifts to a range of larger drop sizes. There are materials