INSECTICIDES, PREVENTIVES, AND MACHINERY. 453 



Gas-tar is sometimes used as a repellent, but is rarely of any 

 practical value ; it protects where it covers, but no further. So 

 tar-water has been used against plant-lice, sometimes with a 

 measure of success ; but it is not sufificiently reliable to make its 

 use advisable for general purposes. 



Naphthaline in the form of crystals volatilizes slowly, and 

 in a close space makes the air unfit for insects ; therefore it is 

 used to protect stored products, and packed with clothing, 

 woollens, or other fabrics in a tight box or closet preserves 

 them from "moths." It has been said that a sprinkling of 

 the crystals on the surface of grain in bins will keep off " moths," 

 "weevils," and similar pests, and, no doubt, that is true to some 

 extent. 



In all that is said here concerning insecticides and their ef!ect, 

 the general experience is quoted ; but it should be remembered 

 that many of them are affected by differences of climate or 

 meteorological conditions. More correctly stated, both plants 

 and insects differ in different regions in their susceptibility to 

 certain insecticides ; hence the progressive and careful farmer 

 will, before trying any of the recommended materials on a large 

 scale, either test them in a small way or inquire of the experiment 

 station or other growers in his vicinity. In general, the state- 

 ments made are based upon the work done in the Eastern, Cen- 

 tral, and Northern United States. 



Bisulphide of carbon is a foul-smelling liquid that volatilizes 

 readily at ordinary temperatures and produces a heavy vapor that 

 is deadly to insects of all kinds when they are confined in a closed 

 space and must breathe it. It is especially useful against species 

 infesting stored products, like grain and other seeds, or even in 

 mills and provision houses where they become overrun with 

 ' ' skippers ' ' or Dermestids. When used to kill insects in bins 

 and closed receptacles, a drachm or, roughly, a teaspoonful to 

 each cubic foot of space, will answer. It should be placed in 

 open vessels on top of the grain in the bin or other receptacle, 

 and the vapor, being heavier than the air, will sink to the bottom, 

 where there should be a few screened openings to permit the 

 escape of the material No length of exposure will injure grain 

 for milling or feeding purposes ; but seed grain may lose germi- 

 nating power if exposed longer than twenty-four hours. Its use 

 against certain plant-lice and other underground insects has been 



