12 MISC. PUB. 526, U. S. DEPT. OF AGRICULTURE 
China clay.—This material is also known as kaolin. It is a white, 
residual clay, and as marketed it is not a definite chemical compound 
but rather any one of several hydrated aluminum silicates. 
Diatomaceous earth and kieselguhr.—These materials may be white, 
light gray, or pale buff. They are the siliceous remains of fossil 
diatoms. 
Gypsum (landplaster)—Chemically this is calcium sulfate 
(CaSO..2H,O),. a white or yellowish-white powder. It is used with 
calcium arsenate in the control of cucumber beetles. 
Hydrated lime-—See page 14. Chemically this is calcium hy- 
droxide (Ca(OH),) and is commonly used with arsenicals and as a 
carrier in nicotine dusts. 
Pyrophyllite—Chemically this is anhydrous aluminum silicate 
(HA1(Si0,),), white, and is very similar to tale in physical prop- 
erties. It has recently come into general use as a diluent for cube 
and derris. 
Sulfur.—sSee page 35. 
Talc—kIn the solid form this material is known as soapstone. 
Chemically it is a magnesium silicate (H,Mg;(SiO;).). As marketed 
as an insecticidal diluent it is usually a white_or grayish-white 
powder composed of microscopic platelike particles that give it a 
smooth feel. It is used in derris and cube dust mixtures. 
Tobacco dust.—-See page 37. 
Walnut-shell flour.—This is a brown powder obtained by finely 
grinding the shells of Persian (“English”) walnuts. It is used in the 
preparation of impregnated dusts. It is not so suitable as tale as a 
diluent for rotenone-containing roots (derris and cube). 
Wheat flour.—This is the ordinary “white” wheat flour. 
DINITRO COMPOUNDS 
These are organic compounds manufactured in this country which 
have come into general use in certain fruit-growing districts for the 
control of scale insects, the fruit tree leaf roller, the pear psylla, the 
eye-spotted budmoth, mites, and aphids. 
They are of two types, (1) those that are sold in powder form to be 
added by the grower to lubricating-oil sprays, and (2) those sold 
in liquid form to be added to water. The former group includes 
dinitro-o-cyclohexylphenol and dinitro-o-cresol. The principal com- 
pound in the second group is sodium dinitro-o-cresylate. Dinitro- 
o-cyclohexylphenol is also used on citrus as a contact insecticide in 
the form of a diluted dust to kill the citrus red mite, and it may be 
used on potato and bean to control the potato leafhopper. 
These materials should be used according to the manufacturers 
recommendations, since they may contain diluents in varying amounts. 
The oil-soluble powdered forms, when added to dormant spray oils, 
generally reduce the quantity of 011 required. 
Dinitro insecticides as now used should be applied to deciduous trees 
only when the buds are dormant. 
When properly used, these compounds present no special hazard 
to human health. 
ESSENTIAL OILS 
Essential oils are volatile, aromatic materials obtained from plants, 
usually by steam distillation, and have odors generally characteristic 
of the plant source. 
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