156 SCIENCE AND FRUIT GROWING 



that the roots were comparatively little affected by the oil : and 

 this conclusion was borne out by experiment on the application 

 of paraffin to the soil in which trees were growing. A number 

 of apples of seventeen years of age were selected, and the ground 

 round them sprinkled with paraffin, either in January or in March, 

 using solar distillate, a lighting oil or petrol in various cases. In 

 every instance the presence of the paraffin in the soil was evident 

 for several months afterwards, yet the trees did not appear to 

 have suffered in any w r ay, either in growth or cropping power 

 (X, 22) ; indeed, in one case, where observations were extended 

 to the second year after the application, the cropping appeared 

 to have been increased by the treatment. Such a result is quite 

 in accordance with what might be expected from the action of 

 paraffin and other antiseptics in increasing the fertility of the 

 soil (p. 249). In these experiments the amount of oil applied 

 varied from one pint to two quarts per tree, and two quarts would 

 be much more than would be likely to reach the ground when 

 the tree was sprayed even with undiluted oil, so that no injury 

 to the soil need be expected from such spraying, and still less, 

 from spraying with a paraffin emulsion. 



(2) The nature of emulsions (VI, 196; VIII, 18; App., p. xxi). 



When paraffin oil is churned up with water, by means, for 

 instance, of a garden syringe fitted with a rose jet, it is broken up 

 into minute globules, which, however, almost at once recoalesce 

 to form an unbroken layer of the oil. But if the water contains 

 a little soap, the globules do not thus coalesce, and, as a result, 

 the liquid remains milky in appearance. On leaving it at rest 

 for some time, these globules rise to the top, just as cream rises 

 from milk, leaving, eventually, the excess of soap solution as 

 a more or less clear liquid at the bottom; rarely quite clear, 

 however, for some of the oil globules are so small that they 

 remain permanently suspended in the liquid. Those that rise 

 to the surface are found to differ in size according to the nature 

 of the oil used, and other circumstances, but are generally about 

 0-0075 mm. in diameter, which is double the diameter of the 

 globules in the cream from milk. A mass of globules, whatever 

 their size may be, provided they are all of the same size, will 

 occupy 74 per cent, of the volume of the cream formed, the remain- 

 ing 2-6 per cent, representing the interstices between the globules, 

 occupied by the liquid in which they are floating, and this is 

 (approximately only, owing to the lack of uniformity in size) 

 the composition of the cream which rises from an emulsion of 



