edly cause
instability, indicated strongly by the ordinary heat test at 80 deg., and to
a less extent by the heat test at 134 deg..

(2) Other compounds exist in more intimate association with the
cellulose nitrates causing instability which cannot be removed by
exhaustive washing with either hot or cold water, by digestion in cold
dilute alkaline solutions such as sodium carbonate, or by extracting
with ether, alcohol, benzene, &c.; these compounds, however, are soluble
in the solvents of highly nitrated cellulose such as acetone, acetic
ether, pyridine, &c., even when these liquids are so diluted with water
or other non-solvent liquids to such an extent that they have little or
no solvent action upon the cellulose nitrate itself. These solutions
containing the bodies causing instability are neutral to test paper, but
become acid upon evaporation by heating. (This probably explains the
presence of free acid when guncotton is purified by long-continued
boiling in water without any neutralising agent being present.)

(3) The bodies causing instability are products or by-products of the
original ester reaction, acid bodies containing nitroxy-groups, but
otherwise of ill-defined characteristics. They combine with the oxides
of zinc or lead, giving insoluble compounds. They are precipitated from
their solutions in diluted acetone upon the addition of soluble salts of
these metals.

(4) Cellulose nitrates are rendered stable either by eliminating these
compounds, or by combining them with the oxides of lead or zinc whilst
still in association with cellulose nitrates.

(5) Even the most perfectly purified nitrocellulose will slowly
decompose with formation of unstable acid products by boiling for a long
time in water. This effect is much more apparent at higher temperatures.

_Dense structureless or non-fibrous cellulose nitrates_ can be
industrially prepared (1) by nitrating the amorphous forms of cellulose
obtained from its solution as sulphocarbonate (viscose). The cellulose
in this condition reacts with the closest similarity to the original
fibrous cellulose; the products are similar in composition and
properties, including that of instability.

(2) By treating the fibrous cellulose nitrates with liquid solvents of
the high nitrate diluted with non-solvent liquids, and more especially
water. The optimum effect is a specific disintegration or breaking down
of their fibrous structure quite distinct from the gelatinis