54 - SECTIONAL ADDRESSES. 
recognition of every change of phase by microscopical examination, making 
use of a technique which has been brought to a high state of perfection, 
gives concrete reality to the study by direct verification of its conclusions. 
To understand more thoroughly the mechanism of these changes in alloys 
and to extend its application to salts, minerals and rocks, we need a fuller 
knowledge of the relation between crystal structure and chemical 
behaviour. Research on the mechanical side is discovering the direction 
of planes of slip in the atomic space lattice under stress, and it remains 
to determine the corresponding planes of greatest and least chemical 
activity towards a given reagent. Next follows the still unsolved query 
as to the nature of the intercrystalline boundary, and the solution of 
these two problems will make it possible to define exactly the chemical 
character of a given aggregate of crystals. The results will be of extreme 
interest for the study of metallurgy, of mineralogy, and of petrology, 
besides filling a serious gap in chemistry, serious because of the extent to 
which solids compose the world around us, and of the part which they 
play in our daily life. 
