8 |
| Denitrated fibre moistened with water | 25 | -- |
| Nitrocellulose: Bronnert's German Patent | | |
| No. 93,009 | 125 | 28 |
| The same after denitration (dry) | 115 | 13 |
| The same after denitration (wetted) | 32 | -- |
| Natural silk | 300 | 18 |
|__________________________________________|___________|________________|

1. Tenacity is the weight in grammes required to break the
thread.

2. Elasticity is the elongation per cent. at breaking.

The numbers are taken for thread of 100 deniers (450 metres of
0.05 grammes = 1 denier). It must be noted that according to
the concentration of the solution and variations in the process
of denitration the constants for the yarn are subject to very
considerable variation.

In regard to the manufacture a number of very serious difficulties have
been surmounted. First, instead of drying the nitrated cellulose, which
often led to fires, &c., it was found better to take it moist from the
centrifugal machine, in which condition it is dissolved (5). It was
next found that with the concentrated collodion the thread could be spun
direct into the air, and the use of water as a precipitant was thus
avoided.

With regard to denitration which is both a delicate and disagreeable
operation: none of the agents recommended to substitute the sulphydrates
have proved available. Of these the author mentions ferrous chloride
(6), ferrous chloride in alcohol (7), formaldehyde (8),
sulphocarbonates. The different sulphydrates (9) have very different
effects. The calcium compound tends to harden and weaken the thread. The
ammonia compound requires great care and is costly. The magnesium
compound works rapidly and gives the strongest thread. Investigations
have established the following point. In practice it is not necessary to
combine the saponification of cellulose ester with complete reduction of
the nitric acid split off. The latter requires eight molecules of
hydrogen sulphide per one molecule tetranitrocellulose, but with
precautions four molecules suffice. It is well known that the
denitration is nearly complete, traces only of nitric groups surviving.
Their reactions with diphenylamine allow a certain identification of
artificial silks of this cl