74 
CHEMICAL HISTORY AND APPLIANCES OF GUN-COTTON. 
upon that described by Schbnbein ; the improvements which the former has adopted, ail 
contribute importantly to the production of a thoroughly uniform and pure gun-cotton; 
there is only one step in his process which is certainly not essential, and about the pos¬ 
sible utility of which chemical authorities are decidedly at variance with General von 
Lenk. 
The following is an outline of the process of manufacture of gun-cotton as practised 
by Lenk. The cotton, in the form of loose yarn of different sizes, made up into hanks, 
is purified from certain foreign vegetable substances by treatment for a brief period with 
a weak solution of potashes, and subsequent washing. It is then suspended in a well- 
ventilated hot-air chamber until ail moisture has been expelled, when it is transferred to 
air-tight boxes, or jars, and at once removed to the dipping tank or vessel, where its satu¬ 
ration with the mixed acids is effected. The acids, of the specific gravity prescribed by 
Schbnbein, are very intimately mixed, in a suitable apparatus, in the proportion origi¬ 
nally indicated by that chemist, i. e. three parts by weight of sulphuric acid to one of 
nitric acid. The mixture is always prepared some time before it is required, in order 
that it may become perfectly cool. The cotton is immersed in a bath of the mixed acids, 
one skein at a time, and stirred about for a few minutes until it has become thoroughly 
saturated with the acids ; it is then transferred to a shelf in this dipping trough, where 
it is allowed to drain, and slightly pressed, to remove any large excess of acid, and is 
afterwards placed in an earthenware jar, provided with a tightly-fitting lid [which re¬ 
ceives six or eight skeins, weighing from two to four ounces each]. The cotton is tightly 
pressed down in the jar, and, if there be not sufficient acid present just to cover the mass, 
a little more is added; the proportion of acid to bo left in contact with the cotton being 
about 10j pounds to one pound of the latter. The charged jars are set aside for forty- 
eight hours in a cool place, where, moreover, they are kept surrounded by water, to pre¬ 
vent the occurrence of any elevation of temperature and consequent destructive action of 
the acids upon the gun-cotton. The same precaution is also taken with the dripping- 
trough, as considerable heat is generated during the first saturation of the cotton with 
the acids. At the expiration of forty-eight hours, the gun-cotton is transferred from 
the jars to a centrifugal machine, by the aid of which the excess of acid is removed as 
perfectly as is possible by mechanical means, the gun-cotton being afterwards only slightly 
moist to the touch. The skeins are then immersed singly into water, and moved about 
briskly, so as to become completely saturated with it as quickly as possible. This result 
is best accomplished by plunging the skeins under a fall of water, so that they become at 
once thoroughly drenched. If they are simply thrown into water and allowed to remain 
at rest, the heat produced by the union of a portion of the free acids with a little water 
would be so great as to establish at once a destructive action upon the gun-cotton by the 
acid present. The washing of the separate skeins is continued until no acidity can be 
detected in them by the taste ; they are then arranged in frames or crates and immersed 
in a rapid stream of water, where they remain undisturbed for two or three weeks. They 
are afterwards washed by hand, to free them from mechanical impurities derived from 
the stream, and are immersed for a short time in a dilute boiling solution of potashes. 
After this treatment they are returned to the stream, where they again remain for several 
days. Upon their removal they are once more washed by hand, with soap if necessary ; 
the pure gun-cotton then only requires drying, by sufficient exposure to air at a tempe¬ 
rature of about 27° C., to render it ready for use. A supplementary process is, however 
adopted by General von Lenk, about the possible advantage or use of which his opinion, 
is not shared by others, as already stated. This treatment consists in immersing the air- 
dried gun-cotton in a moderately strong hot solution of soluble glass (silicate of potassa 
or soda), for a sufficient period to allow it to become completely impregnated ; removing 
the excess of liquid by means of the centrifugal machine ; thoroughly drying the gun¬ 
cotton thus “ silicated,” and finally washing it once more for some time, until all alkali is 
abstracted. Lenk considers that by this treatment some silica becomes deposited with¬ 
in the fibre of the gun-cotton, which, on the one hand, assists in moderating the rapidity 
with which the material burns, and, on the other hand, exercises (in some not very evi¬ 
dent manner) a preservative effect upon the gun-cotton, rendering it less prone to under¬ 
go even slight changes by keeping. The mineral matter contained in pure gun-cotton 
which has not been submitted to this particular treatment amounts to about one per 
cent. The proportion found in specimens which have been “silicated” in Austria and 
in this country, according to Lenk’s directions, varies between 1-5 and 2 per cent. It is 
