146 ELEMENTARY LESSONS ON INSECTS 



2. Contact insecticides. — The most important of these are 

 lime-sulfur and nicotine sulfate. Lime-sulfur kills by its 

 corrosive action upon the tissues. It is used chiefly to kill 

 scale insects on the bark of deciduous fruits during the 

 dormant season, when there are no green leaves to be injured 

 by it. Nicotine sulfate is preferable for summer use. 



3. Fumigants. — These are substances that give off poison- 

 ous gases that, in general, are effective for killing insects 

 only when placed in some sort of inclosure. Carbon bi- 

 sulphide, carbon tetrachloride, fumes of burning sulphur or 

 tobacco, hydrocyanic acid gas, calcium cyanide and calcium 

 fluo-silicate are among them, and the list is still growing. 

 These are all poisonous to man, and must be used with great 

 care. They must not be inhaled. 



Carbon-bisulphide and calcium cyanide are two that are 

 well adapted to many small fumigating operations in closed 

 containers, such as the treatment of unseen pests that get 

 into collections. The former is a heavy ill-smelling liquid, 

 obtainable at any drug or insecticide store. On exposure 

 to the air it gives off a heavy poisonous and explosive gas. 

 The dosage is one pound to 100 cubic feet of space in the 

 box or bin containing the materials to be treated. Expose 

 over night. No light or fire or burning cigar may be allowed 

 near, until the fumes have disappeared. 



Calcium cyanide is available as a dry powder that may be 

 thrown into the container with the infested material. 



All these insecticides, together with ingenious machinery 

 for applying them, are advertised in farm and garden 



