98 SOME SOUTH INDIAN INSECTS, ETC [CHAP. XI. 



whilst Naphthaline Emulsion is also used for special crops such as 

 vegetables, where only a temporary poison is required. Other 

 insecticides of this class include Zinc Arsenite, Dry Paints, and 

 I others which arc more rarely used. 



Lead Chromate is an insoluble yellow substance which is usually 

 sold in the form of a paste containing about 33 per cent, or as a 

 powdei .nut. lining about 50percent.nl Lead Chromate. Thepaste 

 mixes better wit!) water ami is easier t<> use, three ounces of this 

 being taken to represent two ounces of the powder, one-quarter to 

 one-half of an ounce of powder, and half as much again of paste, 

 being the standard dosage for one gallon of water. If Lead 

 Chromate itself is not obtainable it may be prepared by dissolving 

 separately in water one part by weight of Potassium Bichromate 

 ami two parts by weight of Lead Acetate or Lead Nitrate and 

 mixing the two solutions, when two parts bj weight of Lead 

 Chromate will be precipitated, and this may be diluted with water 

 to the required strength and used in the sprayer. 



Lead Chromate possesses these advantages, that its yellow 

 colour makes it readily perceptible mi the plants to which it has 

 been applied and that it is a comparatively weak poison to larger 

 animals such as cattle. It is not, howe\ er, absolutely non-poisonous 

 to cattle, as has been claimed, ami on the other hand, it has not 

 always proved effective against insect-pests; on the whole it does 

 not seem to be sufficiently poisonous to be really effective, but may 

 for the present be recommended as a readily accessible and 

 moderately efficient insecticide for use by those in whose hands it 

 might be dangerous to place arsenicals. 



Lead Arsenate is usually sold in the form of a greyish paste but 

 is also obtainable as a white powder ; in either case it should first 

 be mixed with a little water to make a thin paste before dilution to 

 the strength required for spraying. The advantages of Lead 

 Arsenate are the facts that it does not burn foliage as a rule owing 

 toils insolubility in water, that it remains in suspension in tin 

 tyer with a moderate degree "l agitation, and that it sticks well 

 to tin- surfaces ot plants. The powdered form can be dusted onto 

 plants when the white colour shows up well, but this insecticide is 

 usually applied more economically as a liquid spray. It is con- 

 siderably cheaper than Lead Chromate and a much more violent 

 poison, but does not kill insects so quicklj as Paris Green or the 

 more soluble arsenicals. Lead Arsenate in the form of paste 

 should not contain more than 50 per cent, of water, it should 

 contain more arsenic than is equivalent to 12 1 2 per cent, of Arsenic 

 Pentoxide and should not contain arsenic in water-soluble form 



