4 BULLETIN 
Cakbon Tetrachlorid. 
Carbon tetrachlorid does not differ essentially from carbon di- 
sulphid, in so far as its effect upon the tree or its larvicidal action 
is concerned. To achieve the same result it seemed to require about 
double the dosage of the disulphid. Its chief merit as a fumigant 
seems to lie in the fact that the vapor is not inflammable. 
Naphthalene. 
Naphthalene was tested quite fully in 1916 and 1917. For the 
greater part of the year it vaporized just fast enough to give the 
soil about the base of the tree a pronounced odor, but apparently 
produced no effect upon the insect or the tree. With a soil tempera- 
ture of 70° F. and over, attained in July and August, there is a very 
decided larvicidal action, but not sufficient to make this material of 
value. 
Hydrocyanic-acid Gas. 
Hydrocyanic-acid gas, while a very effective larvicide, proved too 
dangerous. The great solubility of this gas effectually prevents the 
standardization of its use. Variation in moisture content and in the 
type of soil so greatly affect the absorption of this gas by the latter 
that it has been found impossible to establish any standard dosage 
that is both effective and safe for any number of conditions. Moist 
soils required much larger doses than dry soils or soils of low water- 
holding content. This point has been fully covered by Ong 1 in a 
recent publication. The great solubility of the gas, furthermore, 
leads to its rapid absorption by the portions of the tree with which 
it comes in contact, which probably explains in part the considerable 
injury resulting from its use. 
PARA-DICHLOROBENZENE. 
Insecticidal, Physical, and Chemical Properties. 
Of the various volatile compounds tested, the merits of some of 
which have been briefly discussed, para-dichlorobenzene has been by 
far the most promising. While well known chemically, its value as 
an insecticide is of comparatively recent discovery. 
Of the various volatile compounds tested, the merits of some of 
which have been briefly discussed, para-dichlorobenzene has been by 
far the most promising. While well known chemically, its value as 
an insecticide is of comparatively recent discovery. Duckett, 2 in 
1915, published a report on the insecticidal value of its vapor as a 
fumigant against various insects. Later in the same year Cook, 
1 Ong, E. R. de. Hydrocyanic-acid gas as a soil fumigant. In Jour. Agr. Research, 
v. 11, no. 9, p. 421-436. 1917. 
2 Duckett, A. B. Para-dichlorobenzene as an insect fumigant. U. S. Dept. Agr. 
Bui. 167. 1915. 
