372 
Journal of Agricultural Research 
Vol. IX, No. ii 
index of their worth as contact sprays, since Shafer (6) and, more 
recently, Mclndoo (4) have shown that most contact sprays kill by the 
action of their vapor rather than by the plugging of the spiracles. 
COMPOUNDS USED IN THE EXPERIMENTS 
From the hydrocarbon benzene C 6 H 6 a great many compounds may 
be derived by replacement of one or more of the hydrogen atoms by 
certain other elements or groups of elements. These compounds are 
designated “mono,” “di,” “tri,” etc., derivatives, depending on the 
number of hydrogens which are substituted. The following mono-sub¬ 
stitution compounds have been tested in this study: 
Benzonitrile, C 6 H 5 CN 
Chlorbenzene, C 6 H 5 C 1 
Brombenzene, C 6 H s Br 
Iodobenzene, C 6 H 5 I 
Phenol, C 6 H 5 OH 
Anilin, C 6 H 5 NH 2 
Benzaldehyde, C 6 H 5 CHO 
Nitrobenzene, C 6 H 5 N 0 2 
Toluene, C 6 H 6 CH 3 
The following di-substitution products were employed: 
Xylene, C 6 H 4 (CH 3 ) 2 (mixture of the 
three possible isomeres) 
Para-dichlorbenzene, C 6 H 4 C 1 2 
Para-dibrombenzene, C 6 H 4 Br 2 
Ortho-chlorphenol, C 6 H 4 OH Cl 
Ortho-nitrophenol, C 6 H 4 OH N 0 2 
Salicylic aldehyde, CeH 4 0 H CHO 
Besides these di-substitution compounds, several other derivatives were 
used, which may be considered di-substitution compounds of benzene or 
mono-substitutions of toluene. They were ortho- and para-bromtoluene 
(C 6 H 4 CH 3 Br), ortho-, meta-, and para-cresol (C 6 H 4 CH 3 OH), and ortho- 
nitrotoluene (C e H 4 CH 3 N 0 2 ). Inasmuch as different compounds are 
obtained by substitution in the methyl group of toluene rather than in 
the benzene ring of toluene, two such compounds were tested: Benzyl 
alcohol (C 6 H 5 CH 3 OH) and benzoyl chlorid (C 6 H 5 CO Cl). Two deriva¬ 
tives of xylene were tried: Bromxylene (C 6 H 3 (CH 3 ) 2 Br) and nitroxylene 
(C 6 H 3 (CH 3 ) 2 N 0 2 ). 
The xylene used in the experiments was a mixture of ortho-, meta-, and 
para-xylene; hence, the bromxylene and nitroxylene were also mixed 
compounds. 
In this series is shown a wide range of compounds very different in 
chemical composition. A few others were tested but not included, 
owing to their slight volatility. 
METHODS OF EXPERIMENTATION 
One-liter Florence flasks of pyiex glass, closed with rubber stoppers, 
were used as fumigation chambers. As rubber was found to absorb the 
vapor of the chemicals, the stopper was coated with lead foil. Measured 
quantities of the compound to be tested were placed on a piece of filter 
paper cut just as small as possible, the paper was suspended from the 
