INSECTICIDES, FUNGICIDES, ETC. 163 



It would not, however, be safe to assume from these results 

 that the decomposing action of the lighter oils is in itself greater 

 than that of the heavier oils, for the effect produced must 

 depend, not only on the intrinsic chemical activity of the 

 substances, but on their powers of penetration, and on their 

 volatility: the former would increase the effect, whilst the 

 latter, by reducing the amount of oil remaining on the fruit, 

 would diminish this effect. 



The destructive action of paraffin oil cannot be attributed to 

 the accidental presence in it of a certain amount of other oils 

 (unsaturated hydrocarbons) not belonging to the paraffin series, 

 for three different preparations of paraffins, carefully purified 

 from such unsaturated compounds, were examined, and were 

 found to have as great an action on foliage as the commercial 

 oils. 



