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90 On Recent Progress in the History of 
One hundred parts of carefully-purified cotton wool have 
been found by Mr. Abel to furnish from 181°8 to 182°5 
parts of gun-cotton. The increase which perfectly pure 
cellulose should sustain by absolutely complete conversion 
into a substance of the formula C,H,N,O,, (trinitro- 
cellulose) is 83°3; the above results are therefore strong 
confirmations of the correctness of this generally accepted 
view of the composition of gun-cotton. In carrying out 
the actual manufacturing process, as prescribed by Von 
Lenk, somewhat lower results are obtained, because of 
impurities existing in the cotton employed, and of loss of 
product during its purification. 
Very extensive experiments are in progress at Woolwich, . 
with the view of examining fully into the extent of liability 
to change of gun-cotton when preserved in store, or ex- 
posed for prolonged periods to light and to degrees of heat 
ranging between the ordinary atmospheric temperatures 
and that of boiling water. The results hitherto arrived at, 
though they have shown that, under severe conditions, 
gun-cotton is liable to decompose, have not confirmed the 
conclusions arrived at by the French chemists, with regard 
to the great instability of the material. Thus, De Luca 
states that all specimens exposed by him to sunlight 
decomposed either on the first day or within a few days. 
But, at Woolwich, no single instance of such rapid decom- 
position of gun-cotton, made by the present process, has 
been noticed. A very gradual and slight development of 
gas occurs after a time when the substance is exposed to 
sunlight ; but the quantity which has been collected from 
specimens exposed at Woolwich, to direct day and sunlight 
for two years and a half, is very small, and the gun-cotton 
has, in all instances, preserved its original appearance. | 
Pelouze and Maury state that gun-cotton always decom- | 
poses perfectly within a few days, by exposure to tempera- 
tures of 55°—60° C. (130°—140° F.), and they lay great 
stress upon the explosion of a specimen directly it was in- 
troduced into a vessel heated to 47° C. (116°6 F.). But, 
at Woolwich, a specimen of ordinary product which has 
been exposed now for twelve months to 65° C. (150° F.), 
has evolved only a small quantity of gas, and retains its 
original appearance perfectly. Several specimens, after 
having been exposed for some hours to a temperature of 
96° C. (194° F.), during which period some nitrous vapours 
were, in all instances, evolved, have since been exposed to | 
light in closed vessels for about twenty months, and still 
