202 
as a distinct and widely distributed class of substances, and it does not 
seem unreasonable to expect that, when they have received such study, 
important practical uses will follow as a result. There will then be a 
demand for the products yielding them. It is a very remarkable fact 
that we have so high a percentage (from 35 to 80) of volatile sesquiter- 
penes in most of these wood oils, while the resins yielding terpene oils 
very seldom have a content of more than 25 per cent of the latter, and 
the proportion is generally much less. 
I wish to return thanks to Dr. H. N. Whitford, of this Bureau, for 
his valuable and willing help in securing some of the material used in 
this work. 
