The Microscope in the Paper-Mill. 
253 
place during their growth. The summary of the results attained, 
as read before the Eoyal Microscopical Society and published in 
the Transactions, shows how the long-continued study of the details 
of an apparently trifling matter indicates important conclusions 
concerning the deterioration of cellulose in modern paper. 
A problem which has puzzled paper-makers and their chemists 
for nearly a century lies in the sizing of paper with rezin. The 
rezin is added to the pulp in the form of a soap (sodium rezinate 
and dissolved rezin), and precipitated by the addition of aluminium 
sulphite in the form of aluminium rezinate mixed with free rezin. 
The problem may be stated in the question, “ Why does free rezin 
alone, precipitated from the soap with sulphuric acid, yield a sizing 
effect which is not permanent ? ” Some years ago a German 
society offered a premium for a solution to this problem which 
has been propounded perennially without any reasonable solution 
forthcoming. Yet the solution is very simple, and I have observed 
it under the microscope to my own satisfaction. Eezin per se 
precipitated and rubbed over the surface of the fibres, when dried 
behaves as a fluid and flows slowly into the capillary pores of the 
cellulose. A film of alumina precipitated and rubbed over the 
surface of the fibres forms a membrane impermeable to rezin. 
Whether this film is of alumina or aluminium rezinate, or a 
mixture of same is immaterial, the fact is demonstrable. It is 
possible to have an unsized absorbent paper containing 6 p.c. of 
rezin, and a similar paper made from the same fibre, very hard- 
sized and ink-resisting, with only 3 p.c. of rezin, provided the 
alumina is there in sufficient quantity. Very careful observation 
is necessary in work of this kind. The microscopist must train 
his eye for fine detail. The moral of the story of the two micro- 
scopists — one who cannot see the flag ell 8e on a certain bacillus 
with a -f^th oil immersion, and the other who can see it plainly 
with an 8 m.m. objective — is always with us. 
Many years ago when investigating the ash of the leaves from 
various trees and their silica content, I found in many cases a few 
puzzling objects in shape of very minute spherical particles of 
mineral matter. Later I found the same objects in the ash of 
various kinds of paper. As some of the papers were not of wood 
cellulose there was obviously no apparent connexion with the 
trees. I was interested to know where they came from. They 
were perfect spheres, highly siliceous, isotropic, and varied in 
colour from white to brown. Some time later I met my spherical 
friends again while investigating the dust falling from the air in a 
paper-mill. One of them on this occasion was found to contain a 
minute included gas or air-bubble. Here was a clue to their 
origin. They were silicates formed by fusion. A brother micro- 
scopist said they were meteoric dust, and showed me a mount 
collected from a roof. I, however, suspected a humbler origin, 
s 
