12 REPORT—1863. 
fact which is evidently due to the solvent action of the acids upon portions 
of the mineral matter in the cotton. In the place of the comparatively large 
proportions of lime and magnesia in the original cotton, the product which, 
after separation from the acids by very long-continued washing, &e., has 
been submitted to treatment with soluble glass and again washed, contains 
some small quantities (necessarily variable in a product of manufacture) of 
impurities (clay and sand) derived from the water used, and of silicic acid in 
combination with lime and also with soda, minute quantities of the soluble 
glass having escaped removal or decomposition i in the final washing process. 
Supposing that the maximum proportion of silicates (1 per cent.) found in 
the above determinations existed entirely in the form of soluble glass in 
the finished gun-cotton, a piece of twist 12 feet 10 inches in length, and of 
the size used for Artillery purposes (4 inch thick), would contain only one 
grain of soluble glass. It is evident therefore that no protective effect nor 
retardation in the explosion of the gun-cotton can result from the treatment 
with soluble glass to which it is submitted. 
Experiments on the Hygroscopic Properties of the Austrian Giun-cotton. 
(8) It has already been stated that the proportion of moisture contained, 
under normal conditions, in the specimens of Austrian gun-cotton was found 
to be very uniform, the mean proportion being fixed at 2 per cent. by the 
results of several experiments. 
Some gun-cotton prepared from ordinary cotton-wool, and haying the same 
composition as the Austrian samples—but not having been submitted to the 
preparatory or subsequent treatment with alkali, nor to the very long-con- 
tinued washing—was examined with regard to its hygroscopic properties, 
in comparison with the Austrian gun-cotton. The proportion of moisture 
existing in the former, under ordinary conditions, was found to be almost 
identical with the average proportion in the Austrian samples. 
Some experiments were instituted to ascertain the rate at which the 
Austrian gun-cotton would absorb moisture, on exposure to a damp atmo- 
sphere. 
The specimens experimented with were first thoroughly dried in vacuo 
over sulphuric acid, and then exposed for successive periods, together with a 
shallow vessel containing water, under a capacious bell jar placed in a 
moderately warm room. The following results were obtained :— 
Specimen. Period of exposure to a damp atmosphere. 
1 hr. 2hrs. 4hrs. 20hrs. J30Ohrs. 72 hrs. 
Nos lari. . -aeop ae w. 3:15 .. 3°87 
Ans ap,ee= 100 ae Se 3-21 Ke 3°65 
fae 1:89 2:15 ae 3°55 
4. $i 1:73 2:00 ve 3:21 36 
5. 1-77, ~ 221 be Re ‘. 3:90 
These results show that the rate of absorption of moisture by the gun-cotton 
is uniformly rapid up to the point where 2 per cent. (the normal proportion 
of hygroscopic moisture) have been absorbed, and that, when this point has 
been attained, the absorption of further moisture proceeds comparatively 
very slowly*. Several experiments were made to determine, as far as possible, 
* Several determinations of the moisture in cotton rovings, both before and after treat- 
ment with alkali (and repeated washing), show that the proportion of hygroscopic moisture 
in the cotton amounts to between 6 and 7 per cent., this amount being reabsorbed by the 
dried cotton, within twenty-four hours, on exposure to air. 
