OILING THE WAVES. 29 



Oils vary so greatly in their rate of outspreading over water 

 and the character of the film they form, that some years ago 

 Mr. Moffatt, of Glasgow, proposed to use these differences as 

 a test for the adulterations of one kind of oil with other and 

 cheaper kinds. 



I made a number of experiments, verifying some of his 

 results. 



From these it is evident that the duration of the becalming 

 effect will vary with different oils, and therefore further 

 experiments upon these differences should be made, in order 

 to select that kind which is the most effective, with due 

 regard, of course, to cost. 



The oil indicated by my experiments as combining perma- 

 nency and cheapness, and altogether the most suitable and 

 attainable, is the " dead oil" refuse of the gas-works. This 

 may be used in its crude and cheapest condition. 



