supports      '	243
deteriorate because they are more easily hydrolyzed and oxidized. Certainly
experience with papers has shown that, in general., those made from cotton-group
fibres are far more stable as to color and consistency than those as yet made from
the wood-pulp group.
Besides the fibres themselves or any impurities that go with them, paper may
contain other materials added for the purpose of giving it certain kinds of surface
properties. Loading materials, chiefly China clay, are used mainly in the manu-
facture of the coated or glossy papers required for some kinds of printing. Sizing
materials are more common and are apt to appear in western products of the
present day except in blotting and filter papers. Glue and starch used for sizing
seem to have only a slightly harmful effect. They are apt to increase a tendency
towards the development of mold and micro-organisms. Rosin, on the other
hand, is definitely a bad addition to paper fibre, for in a fairly short time it be-
comes dark and brittle.
The most serious and rapid breakdown of paper probably takes place in these
added materials, if the fibre itself is pure. Fibrous cellulose is naturally very
inert and resistant but it has a number of points where it is vulnerable. It de-
composes at 250° C. and the products are complex and numerous. Evidently it is
able to withstand effects of atmospheric oxygen to a large extent. It is even
resistant to the action of weak oxidizing agents and bleaching solutions. This
resistance has a definite limit, however, and when the strength of the solution
becomes too great, destruction takes place. The products are chiefly oxalic and
carbonic acids and there are left, also, the residues known as oxycelluloses. These
vary according to the oxidizing agent, its strength and temperature, and according
to hydrolytic reactions that occur at the same time. In all cases., they are weak,
friable substances and no means are known for converting them back into cellu-
lose. Pure cellulose is attacked by dilute acids and produces either dextrins and
dextrose, soluble substances, or insoluble materials called hydrocelluloses. The
effect of micro-organisms on cellulose is well known; bacterial fermentation is the
means by which it is digested. And it has been noticed that many such organisms
are able to develop and to decompose cellulose in a free supply of air. Mold'is an
enemy of paper and is doubtless responsible for much of its discoloration. The
brown spots or * foxing* so familiar in old books, prints, and drawings are ap-
parently stains caused by the decomposition of mold and micro-organisms. It
seems probable, however, that mold itself is little apt to grow on pure cellulose
and that its first nourishment at least comes from added materials, chiefly animal
glue and casein.	^: ...
The ancient papyrus was made directly from the paper reed, Cyperus papyrus
of Linnaeus. This was cut into long strips and those from the center of the plant
were found to be the broadest and the most valuable. The strips were laid out,
so that they crossed at right angles, on boards and were soaked In water (tradi-
tionally that of the Nile). After soaking, the web formed by the crossed strips