491 



result of this will be the appearance on the market of cheaper and less 

 reliable arsenicals, such as calcium arsenite and calcium arsenate. 

 The requisites for an insecticide that is to be applied as a spray are : - 

 toxicity to the insect and non-toxicity to the plant ; adhesiveness 

 under all weather conditions ; fineness of particles and low specific 

 gravity to ensure a higii power of suspension and uniform distribution ; 

 abihty to indicate the leaf-surface covered ; and reasonable cost. 

 All arsenical compounds are poisonous, though, as a rule, the lower, 

 or arsenite salts are more active than the higher, or arsenate ones. 

 Arsenic that is soluble in water, or that has been rendered soluble 

 by atmospheric agents, has a corrosive action on foliage to the extent 

 of entire defoliation in severe cases. Therefore an arsenical must 

 be insoluble and stable in water or in whatever liquid vehicle is used 

 for its application. 



These conditions are fulfilled by calcium arsenite, which, with excess 

 of lime, has a good power of suspension, and by the deposition of a 

 white film readily indicates the leaf-surface covered. 



The use of sodium arsenite, on the other hand, by inexperienced 

 persons camiot be recommended, owing to its solubility. 



Acid calcium arsenate is soluble in water but practically insoluble 

 in lime water, which indicates that its safe application necessitates 

 an admixture with Bordeaux or strong milk of lime. It contains 

 a high percentage of arsenic, and may serve in many instances as a 

 substitute for acid lead arsenate during the present emergency. 

 Experiments to test its efficiency are in progress. 



Moore (W.). Fumigation with Chlorpicrin. — Jl. Econ. Entom., 

 Concord, N.H.. xi, no. 4. August 1918, pp. 357-362. 



The fact that chlorpicrin, though rather a volatile compound, is 

 extremely toxic to insects [see this Review, Ser. B, v, p. 174] has 

 raised the question of its possible use in the fumigation of grain and 

 clothing. Its value as a fumigant for destroying the body louse 

 {Pediculus humanus) and its eggs has also been recorded [see this 

 Review, Ser. B, vi, p. 189]. 



The advantages in the use of chlorpicrin, as compared with carbon 

 bisulphide, are : — that its toxicity, molecule for molecule, is about 

 283 times as great as that of carbon bisulphide ; its use, unlike that 

 of the highly inflammable carbon bisulphide, is not dangerous under 

 normal conditions, though it, too, may be exploded when heated : 

 owing to the severe irritation caused to the eyes, nose, and throat by 

 minute quantities, there is very little risk of an injurious amount 

 being inhaled, while carbon bisulphide, though unpleasant, may be 

 inhaled in sufficient quantities to cause death ; its vapour, being 

 about twice as heavy as that of carbon bisulphide, which, in its tarn 

 is about 2 '5 times heavier than air, is particularly suitable for the 

 fumigation of grain owing to its being able to sink down througb 

 large masses. 



Experiments on the last point have proved that one half pound oi 

 chlorpicrin per 1,000 cubic feet will prove destructive to Bruchus 

 obtectus. Say (bean Bruchid), Sitotroga cerealella, Oliv. (Angoumois 

 grain moth), Plodia interpanctelki, Hb. (Indian meal moth), and 

 Ephestia kuhniella, Zell. (Mediterranean flour moth), but is not sufficient 

 (C514) b2 



