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chemical. The beating process, whereby the cellulose is broken 
up mechanically and rendered colloidal to varying degrees, is 
largely physical. The processes of sizing and colouring paper- 
stock present numerous physico-chemical problems. 
Variations in the methods of conducting such processes pro- 
duce a variety of results which are taken advantage of by the 
practical paper-maker in the production of desired physical proper- 
ties in the many kinds of paper made for particular purposes. 
The practical paper-maker works largely by rule-of-thumb methods 
based on past experience. If he gets a certain result by a process 
of trial ending successfully, to obtain the same result in future he 
will repeat the same process exactly, although in doing so he 
may perpetuate an indirect method involving useless error and 
correction. 
The constant use of the microscope reveals the fact that all 
variations in the chemical and physical treatment of cellulose are 
accompanied by changes in the structures and micro-chemical 
properties of the fibrous material. Some of these changes are 
slight but perfectly definite when closely studied under the micro- 
scope. The importance of such detail is obvious. An exact 
knowledge takes the place of vague descriptions, and the peculiari- 
ties of masses thus described are more exactly described, and to 
some extent explained, in terms of the individual constituents and 
elements. In this work both polarized light and dark -ground 
illumination are almost indispensable. 
Such a knowledge of detail gained by use of the microscope is 
invaluable when applied in the control of practical processes. 
The application of the microscope in this direction in the paper- 
mill is still in its infancy, but promises to be a most interesting 
and valuable field of work. 
5. Study of Microscopical Detail Widens the 
Mental Outlook. 
It is generally recognized that a continued study of detail is 
apt to dwarf the imagination, but when such study is developed 
over a wide enough field, and always with practical issues in view, 
the reverse is the case, and a correlated and collated mass of detail 
stimulates the imagination. 
About twenty years ago I commenced the study of the peculiar 
dendritic growths arising in paper from particles of copper and 
bronze embedded in the fibres. These growths supplied the 
amateur microscopist with pretty objects, but were regarded as a 
bit of a nuisance by the practical paper-maker. My object in 
studying them was not so much their prevention, which is a simple 
enough matter, as the nature of the chemical reactions taking 
