in the proportions of 66 per cent. and 34 per cent. respectively. (The production of the penta-nitro-cellulose is aimed at if the collodion-cotton is for use as an explosive.) If the acids are much weaker than this, or potassium nitrate and sulphuric acid is used, the lower nitrates will be formed.  The product, while being entirely soluble in ether-alcohol or nitro-glycerine, will have a low nitrogen content, whereas a material with as high a nitrogen as 12 or 12.6 is to be aimed at.

[Footnote A:  Raw cotton is often used.]

The cotton should not be allowed to remain in the dipping tanks for more than five minutes, and the acid mixture should be kept at a temperature of 28 deg.  C. or thereabouts; and the cotton should be removed after a few minutes, and should not be pressed out, as in the case of gun-cotton, but at once transferred to the pots and allowed to steep for forty-eight hours. (Some prefer twenty-four hours, but there is more chance in this case of the product containing non-nitrated cellulose.) When the nitration is complete, the collodion-cotton is removed from the pots, and treated in exactly the same manner as described under gun-cotton.  The produce should be entirely soluble in ether-alcohol and nitro-glycerine, and contain as near 12.7 per cent. of nitrogen as possible.  The theoretical nitrogen is for the penta-nitro-cellulose 12.75 per cent.  This will, however, seldom if ever be obtained.  The following are some of the results I have obtained from different samples:—­

Nitrogen.
(1.)  (2.)  (3.)
German make   11.64  11.48 11.49 per cent. 
Stowmarket    12.57  12.60 11.22    "
Walsrode      11.61  12.07 11.99    "
Faversham     12.14  11.70 11.60    "

and the following was the analysis of a sample (No. 1) of German-made collodion-cotton, which made very good blasting gelatine:—­

_
Soluble cotton (collodion) 99.118 per cent.| Nitrogen = 11.64 per cent. 
Gun-cotton                  0.642   "     _|
Non-nitrated cotton         0.240   "
Total ash                   0.25    "

It should contain as little non-nitrated or unconverted cotton and as little gun-cotton as possible, as they are both insoluble in nitro-glycerol.  The quality and composition of any sample of collodion-cotton can be quickly inferred by determining the percentage of nitrogen by means of the nitrometer and the use of the solubility test.[A] A high nitrogen content coupled with a high solubility is the end to be aimed at; a high nitrogen with a low solubility shows the presence of gun-cotton, and a low nitrogen, together with a low solubility, the presence of unnitrated cotton.  Where complete solubility is essential and the percentage of nitrogen less important, Dr Lunge recommends nitration with a mixture of equal parts of sulphuric and nitric acids containing from 19 to 20 per cent. of water.

[Footnote A:  See Analysis of Explosives.]