344 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



naphthalene distils between 210" and 220° C. It is collected in conical 

 wooden vessels slightly moist, in which it solidifies in a few hours. 

 By reversing the moulds, cakes of pure naphthalene are obtained. 

 For agricultural purposes crude naphthalene may be used. It is 

 rarely used alone. It is mixed with such substances as plaster, lime, 

 wood ashes, or sawdust, is drenched with fused or dissolved naph- 

 thalene. A great use is made of a mixture of tar, naphthalene, and 

 lime, brought out bj^ Balbiani, and named after the inventor, Balbiani's 

 ointment. It is prepared thus : Slake 120 lb. fat quicklime in lumps 

 by pouring on to it a small quantity of water from a watering-can. The 

 heat disengaged by the hydration of the lime is used to melt 20 lb. 

 of coal tar, and 60 lb. of crude naphthalene, which is run into the 

 lime whilst it is still steaming. The whole is kneaded by an iron 

 stirrer. Whilst continuing to stir the mixture a little water is added so 

 as to sustain the heat of the lime and to keep the mixture pasty. 

 When the lime is slaked no more water is added, the ointment is 

 finished when the paste is homogeneous. Solutions of naphthalene 

 in benzene and alcohol are also used at the rate of 1 part of 

 naphthalene for 8 parts of solvent (say 1 lb. to a gallon). 



Properties. — Pure naphthalene forms white scales with a strong 

 odour and a bitter aromatic taste. Insoluble in cold water, very 

 slightly soluble in boiling water, naphthalene is soluble in alcohol and 

 benzene. 



Action on Plants. — Naphthalene does not appear to injure 

 plants ; benzene solutions, according to Debray, have no injurious 

 action on the leaves. Mohr's opinion is, however, that this solution 

 injures the parenchyma of plants. The germinative capacity of seed 

 which has been even in prolonged contact with naphthalene is not 

 diminished. 



TABLE LXXIII. — Showing Action of Naphthalene on Germinative Capacity of 

 Cotton Seed. 



Action on Insects. — The experiments of Dufour have shown that 

 naphthalene, so to speak, has no action on caterpillars ; however, its 

 smell is so disagreeable to insects in general that this substance drives 

 them off and eradicates them at the time of laying their eggs. The 

 vapours of naphthalene stupefy insects, but they recover in the fresh 

 air. 



Use. — Naphthalene enters into the composition of many anticrypto- 



