KEROSENE EMULSION. 81 



by means of the hand sprayers, and it should be kept for this purpose. 



On farms, it is useful against many pests which attack valuable crops 

 and render useless the results of other experiments whose value is shown 

 by comparative yields. Every experimental farm should keep and use 

 lead arseniate, applying it with a good spraying machine and in powder 

 form. It is obtainable from chemists at Re. 1 per Ib. in powder or paste 

 form. The paste contains 33 per cent, of water, and 1| Ibs. of paste 

 are sold as one pound of lead arseniate and should be used as one pound 

 in mixing with water before spraying. 



Kerosene Emulsion. 



The most useful and simple contact poison is kerosene, the ordinary 

 refined kerosene used for burning in lamps. It kills all insects when 

 applied to their bodies, though its action is not fully understood. It 

 acts partly by mechanically closing the respiratory openings on the side 

 of the body, thereby asphyxiating the insects ; possibly it has a directly 

 poisonous effect on the tissues of the insects when the vapour is absorbed 

 through the system of air tubes which penetrate the body. Applied by 

 itself, kerosene kills the parts of the plants on which it is placed so that 

 the application of undiluted kerosene is as a rule fatal to plants. It 

 has therefore to be applied in a diluted form, and, as it does not mix with 

 water, it is made into an emulsion with soap and water. An emulsion 

 of kerosene consists of water with kerosene in very minute drops ; and on 

 applying such an emulsion, the water evaporates leaving a minute 

 quantity of kerosene on the plant, which is fatal to the insects, but does 

 not injure the plant. The value of kerosene emulsion lies simply in the 

 fact that it can be applied at such strength as to be fatal to many 

 insects and yet not injurious to the tender tissues of the leaf. 



Kerosene emulsion is prepared by boiling a solution of soap and 

 water, adding kerosene and agitating or beating up the mixture so as to 

 break up the oil into very minute drops, which gives the liquid a creamy 

 white appearance. Such an emulsion can be made very strong and 

 afterwards diluted with cold water to the proper strength for applying to 

 plants. In cold countries, kerosene can be applied to leafless dormant 

 trees in much greater strength than in hot climates. In India a 

 strength of 10 per cent, of kerosene can rarely be exceeded. Kerosene 

 has a peculiar way of " wetting " or penetrating insects which are 

 protected by a covering of mealy white wax. It is therefore particu- 

 larly effective against mealy bugs. It kills aphis (Green-fly), the softer 

 scale insects, green bugs, small sucking insects and also some of the 



