xxxlv Remedial Measures and Insecticides. 



combination, loses its own objectionable properties. The most 

 important part of the process is the churning. This must be most 

 thoroughly carried out. It can be satisfactorily managed by 

 repeatedly drawing up and expelling the mixture through an 

 ordinary garden syringe or a force-pump. A more lengthy 

 method is to stir the mixture vigorously with a whisk of twigs. 

 The liquid should be boiling hot during emulsification, and then, if 

 kept in a cool place, it is said to last for a year or more without 

 separating. If insufficiently churned, the mixture will afterwards 

 become separated, and the oil collect at the top. A properly 

 compounded emulsion will mix with water in any proportions. 



For use against scale insects a strength of one part emulsion 

 to ten of water is found to be effective. As in all preparations of 

 which petroleum is an ingredient, it can be more safely used on 

 cloudy days. When used in hot sunshine, it is liable to burn the 

 foliage and injure the tender shoots of the plant, but the danger of 

 injuring is much less with a properly prepared emulsion than with 

 mechanical mixtures of kerosene and water. Mr. Marlatt, in some 

 ' Notes on Insecticides,'* gives the following particulars of experi- 

 ments which show that kerosene emulsion can be be used of con- 

 siderable strength without causing appreciable injury to the plants. 

 But it cannot be recommended for general use at a greater 

 strength than mentioned above. Mr. Marlatt writes : 'About the 

 1st May, when the foliage was in the vigour of its early growth, 

 a number of plants — peach, Japan quince, elm, pine, and straw- 

 berry — were treated with the following strengths of kerosene and 

 whale-oil soap emulsions, made after the standard formula: Diluted 

 (i) with 2 parts of water, (2) 4 parts of water, (3) 9 parts of water, 

 and (4) 14 parts of water, or the emulsion at \, i, jV. and tV 

 strength. The application was very thorough, and the limbs and 

 twigs were thoroughly wetted by immersion in the insecticide. 

 The treatment was made on a very bright, warm day, in the early 

 afternoon. No rain occurred for four days, after which there were 

 heavy rains. No injury whatever developed in the case of the 

 pine, strawberry, and elm with any of the strengths used. With 

 peach the injury was trifling, a very small percentage, perhaps one 

 or two per cent, of the leaves turned yellow and fell to the ground, 

 but I am inclined to believe that this was merely the normal 

 spring shedding of the leaves, which is seen in nearly all plants. 



* Insect U/e, vol. vii. p. 116. 



