11 
so no one rule of application can be employed in all cases, and it thus 
becomes necessary to understand the influence of various factors that 
proper allowance may be made for them and the destruction of the 
insects attained without injuring the plants. 
- Moisture—Carbon bisulphid evaporates most rapidly in a warm, dry, 
sandy soil, and the persistence of the vapor is also shortest in such soil. 
In fact it diffuses so rapidly that most insects will survive an ordinary 
dose; and if the dose is increased so as to kill the insects, it is ikely to 
kill the vines as well. The treatment can not be successfully applied 
on such a soil in its dry condition. On the other hand, diffusion is 
slowest in heavy, wet, clay soil; and, when such soil is saturated with 
water, it is almost entirely prevented. Moisture lowers the tempera- 
ture and decreases the permeability of the soil; it also prevents the 
evaporation of the liquid, and thus retards diffusion. Between these 
two extremes there is a medium condition of moisture which is most 
favorable for treatment. 
Character of soil—Sandy soils permit an even but too rapid diffusion 
of the vapor. Rocky soils are not of even texture, and naturally the 
vapors follow the lines of least resistance. Heavy clay soils, when 
very dry, are usually much broken by cracks and fissures, which may 
run from the surface to a considerable depth. Through such fissures 
the vapor escapes rapidly without permeating the soil to any extent, 
and its insecticidal value is therefore slight. But when such a soil is 
well moistened it is even in texture and very favorable to treatment. 
Depth of soil— The depth of the soil is an important factor in deter- 
mining how much carbon bisulphid must be used for a given area. If 
the soil is shallow and the subsoil very dense and impervious, it is evi- 
dent that much less liquid will be required to produce a death atmos- 
phere than will be needed in a soil of much greater depth. In soils of 
the same character and condition the amount needed will be propor- 
tional to the permeable depth of the soil. In heavy, compact soils 
increase the number of injections and diminish the dose; in light, deep, 
permeable soils decrease the number of holes and increase the dose. 
Amount to use.—In field experiments with the grape, using plain 
carbon bisulphid in ‘*‘ quite fresh” soil, vines were found to withstand 
105 c. ¢. of carbon bisulphid (4.4 ounces, nearly), divided equally 
among 3 holes placed about 16 inches from the base of the vine and at 
a depth of about 20 inches; but 180 ¢. c. (74 ounces) proved fatal to 
the vines. In a warmer, drier, more shallow soil a dose of 90 c. ¢. per 
vine, similarly placed, proved fatal. After considerable rain, when 
the ground was quite wet, a vine withstood 260 c. c. of carbon bisul- 
phid, and some vines are said to have withstood 400 c. e. 
Conditions favorable to treatment.—The treatment should never be 
applied for some time after plowing or cultivating, as a firm, compact, 
moist surface is much more favorable to the retention of the vapor. 
