300 Agricultural Chemistry. 



"Dips" which have proved very efficient in destroying sheep 

 ticks have given sodium arsenite recognition as a valuable in- 

 secticide. The following formula has been used with success : 



Arsenite of soda 5 pounds 



Soft soap 5 pounds 



Aloes 12 ounces 



Water 100 gallons 



The soap is said to increase the retention of the dip on the 

 fleece and aloes renders it distasteful to the animal and prevents 

 poisoning. Sodium ar 'senate has been used against locusts by 

 adding it to sugared water and spraying the grass in the infested 

 region. 



Lead arsenate was recommended as an insecticide in 1892 and 

 was first used against tent caterpillars. It is prepared by adding 

 lead acetate to sodium arsenate in water. These substances dis- 

 solve readily in the cold and react to form sodium acetate and 

 lead arsenate. the latter remaining suspended as a fine white 

 powder. This insecticide should be handled in the form of a 

 paste, for once dried it is suspended with difficulty. Recent ex- 

 periments show that lead nitrate is to be preferred to the acetate 

 in making the arsenate because the product remains in suspension 

 better and contains more lead-hydrogen- arsenate, carrying a 

 higher percentage of arsenic than is the case with preparations 

 from the acetate. This is apparently the most insoluble of all 

 the arsenical insecticides and least likely to scorch the foliage. 

 Headden has shown, however, that care should be taken to use 

 pure water in the preparation of even this spraying mixture. 

 Solutions of 0.1 per cent sodium sulphate or 0.05 per cent com- 

 mon salt dissolve considerable amounts of arsenic from lead ar- 

 senate. Practical spraying tests with lead arsenate in distilled 

 water showed that sodium carbonate or sodium chloride at the 

 rate of 10 grains per gallon in the spray fluid produced severe 

 injury and 40 grains of the latter salt per gallon injured about 

 50 per cent of the foliage. Salt waters and alkali surface waters 

 must therefore be avoided. 



