THE CONTROL OF INJURIOUS INSECTS 385 



cent. AS2O5, but does not remain well in suspension. The powder 

 form is used in dust spraying. 



Sometimes a gallon of molasses is added to 40 gal. of the solution 

 with good effect against fruit-flies, rose-chafers and grape root-worm 

 beetles. Arsenate of lead can be used safely with the Hme-sulphur 

 mixture for summer sprays. 



(d) Arsenate of Lime. — Recently arsenate of lime or calcium 

 arsenate has given good results against certain chewing insects. It 

 may be prepared according to the following formula: 



Stone lime (90 per cent. CaO), 55 lb.; sodium arsenate (dry pow- 

 dered), 65 per cent. AS2O5, 100 lb.; water, 26 gal. 



2Na3AsOi + 3Ca(OH)2 = Ca3(As04)2 + 6NaOH. 



The lime is slaked in a small amount of water; while slaking is taking 

 place the sodium arsenate, dissolved in hot water, is poured in; sufficient 

 water is added to prevent burning. The calcium arsenate formed in 

 this way contains about 18 per cent. AS2O5. 



The killing action is about equal to that of lead arsenate, perhaps 

 a little slower, when used at the rate of 2 lb. to each 50 gal. of water. 

 It can be used with hme-sulphur as a combined insecticide and fungi- 

 cide. It can be prepared more cheaply than lead arsenate.^ 



Arsenate of lime, when used alone as a spray, is liable to burn 

 the leaves, but when used in combination sprays with Bordeaux 

 mixture, lime sulphur, and sodium sulphide ("Soluble sulphur," 

 " Sulphocide ") it is as safe as any other arsenical and probably 

 the cheapest of all insecticides. 



{e) Hellebore. — This substance is sometimes used as a substitute 

 for arsenicals on fruit which is nearly ripe. It may be applied dry or 

 liquid; dry with five parts of flour or air-slaked lime, liquid at the 

 rate of i oz. of hellebore to 2 gal. of water. 



Although an internal poison to insects it is harmless to man in the 

 quantities named. It is too expensive for use on large areas. 



(/) Sodium Fluoride. — Acts both as a poison and a contact substance. 

 Applied as a fine powder or dust pure or mixed with flour or lime. 

 Effective against ants, cockroaches, etc. 



^Some chemists maintain that arsenate of lead, when added to Bordeaux, is 

 converted into arsenate of lime; hence it is more economical to add arsenate of 

 lime in the first place. 

 23 



