n 60-63
p.ct. PbO and 3.5 p.ct. N (obtained as NO).

In further confirmation of the conclusion from these results, viz. that
the nitrocelluloses with no tendency to combine with PbO are associated
with acid products or by-products of the ester reaction combining with
the oxide, the lead reagent was allowed to react in the presence of 90
p.ct. acetone. Water was added, the disintegrated mass collected, washed
with dilute acetic acid, and finally with water. Various estimations of
the PbO fixed in this way have given numbers varying from 2 to 2.5 p.ct.
Such products are perfectly stable. This particular effect of
stabilisation appears, therefore, to depend upon the combination of
certain acid products present in ordinary nitrocelluloses with metallic
oxides. In order to further verify this conclusion, standard specimens
of cellulose nitrates have been treated with a large number of metallic
salts under varying conditions of action. It has been finally
established (1) that the effects in question are more particularly
determined by treatment with salts of lead and zinc, and (2) that the
simplest method of treatment is that of boiling the cellulose nitrates
with dilute aqueous solutions of salts of these metals, preferably the
acetates. The following results may be cited, obtained by boiling a
purified 'service' guncotton (sample C) with a 1 p.ct. solution of lead
acetate and of zinc acetate respectively. After boiling 60 minutes the
nitrates were washed free from the soluble metallic salts, dried and
tested.

__________________________________________________
| | | |
| | Heat Test | Heat Test |
| | at 80 deg. | at 134 deg. |
|__________________________|___________|___________|
| | | |
| Original sample C | 10 | 41 |
|Treated with lead acetate | 67 | 45 |
| " zinc " | 91 | 45 |
|__________________________|___________|___________|

In conclusion we may briefly resume the main points arrived at in these
investigations.

_Causes of instability of cellulose nitrates._--The results of our
experiments so far as to the causes of instability in cellulose nitrates
may be summed up as follows:--

(1) Traces of free nitrating acids, which can only occur in the finished
products through careless manufacture, will undoubt