fATE X . ~> January 1942 ET-188 United States Department of Agriculture Bureau of Entomology and Plant Quarantine A DUST-MIXING APPARATUS FOR PREPARING SMALL QUANTITIES OF COATED OR IMPREGNATED DUST FOR LABORATORY USE By T. A. Brindley, W. E. Peay, and F. G. Hinman, Division of Truck Crop and Garden Insect Investigations Recent developments in the use of materials containing rotenone for insecticidal purposes indicate that in many cases mixtures prepared from extracts of rotenone-bearing roots were more toxic than mixtures prepared from the finely ground roots. Existing laboratory methods of mixing were not satisfactory for preparing small quantities of dust mixtures when the object was to coat or impregnate as many particles of the carrier as possible with the liquid extract. Most methods used to add liquid materials to dust simply involve the addition of the liquid materials to the carrier by pouring them in or spraying them onto the carrier as it is being tumibled in some type of mixer. Such methods often re- sulted in mixtures in which the added liquids caused the formation of pellets of carrier and liquid which were difficult to break up. The apparatus shown in figure 1 seemed to overcome this difficulty to a major extent by adding the liquid in an atomized form to a cloud of dust in a mixing chamber. This was accomplished through the use of the nozzle shown in figure 2. A jacket per- forated by a number of holes v/as built around a DeVilbiss atomizer. A cloui of dust could be blown through the perforated jacket while a liquid was being sprayed from the atomizer. The cloud of dust and the atomized liquid were confined in a mixing chamber as shown in figure 1. This chamber is 24 inches long and 10 inches in di- ameter and is closed at the ends by two plates held in place by thumb screv/s. The chamber is made tight by rubber gaskets. The liquid is measured into a calibrated vial attached to the atomizer. The dust is weighed and placed into an apparat'-^s for applying dust quantitatively (described in ET-45, April 1935). Air pressure maintained at 10 pounds per square inch was found to be sufficient to move the dust into the mixing chamber from the uniform dust applicator. The movement of dust and liquid into the mixing chamber is synchronized by eye. In order to prevent a build-up of pressure in the mixing chamber, which prevents an even flow of the liquid materials, five air outlets one-half inch in diameter were cut in the plate opposite - 2 - to that through '^hich the liquid and dust were introduced. These air outlets v;ere covered by several layers of cheesecloth, which per- mitted the escape of excess air pressure and reduced the loss of dust to a minimum. The results achieved in mixing several different dust mix- tures with this apparatus are shovai in table 1, Table 1. — Check analysis of materials mixed in laboratory dust-mixing apparatus Mixed to contain Amount actually Amount recovered. the amcun it indicated. contained, based based on analyses Field based on the on analysis made made by Division station manufactu irer's by Division of of Insecticide sample analysis of derris Insecticide Investigations No. extract Investigations (percent) 1/ I2. ercent) 2/ (percent) 20 0.25 0.15 0.22 25 0.25 0.15 0.17 31 0.25 0.15 0.12 22 0.50 0.31 0.29 24 0.50 0.31 0.43 30 0.50 0.31 0.34 21 0.75 0.46 0.47 26 0.75 0.45 0.47 29 0.75 0.46 0.47 19 1.00 0.61 0.74 23 1.00 0.61 0.64 28 1.00 0.61 0.62 1/ Manufacturer's analysis, 38.4 percent rotenone . 2/ Insecticide Division analysis, 23.5 percent rotenone. Figure 1. — Dusting-mixing apparatus for in5)regnating or coating carriers with liquid materials. Figure 2. — Nozzle arrangement used on dust-mixing apparatus, This nozzle consists of a DeVilbiss atomizer with a dust nozzle built around the atomizer outlet. ■. UNIVERSITY OF FLORIDA 3 1262 09240 9555