Examination of Nitrated Celluloses with Polarised Light.—­Dr G. Lunge (Jour.  Amer.  Chem.  Soc., 1901, 23 [8], 527) has formed the following conclusions:—­The most highly nitrated products appear blue in polarised light, but those containing between 13.9 and 13.0 per cent. of nitrogen cannot be distinguished from each other by polarisation.  As the percentage of nitrogen rises, the blue colour becomes less intense, and here and there grey fibres can be observed, though not in proportion to the increase in the nitrogen.  Below 12.4 per cent. of nitrogen, the fibres show a grey lustre, which usually appears yellow when the top light is cut off.  Below 10 per cent. of nitrogen, the structure is invariably partially destroyed and no certain observations possible.  It is only possible to distinguish with certainty, firstly any unchanged cellulose by its flashing up in variegated (rainbow) colours; and secondly, highly nitrated products (from 12.75 per cent.  N upwards), by their flashing up less strongly in blue colours.  The purple transition stage in the fibres containing over 11.28 per cent. of N (Chardonnet) was not observed by Dr Lunge.

Determination of Nitrogen by Lunge Nitrometer.—­The determination of the percentage of nitrogen in a sample of gun-cotton or collodion is perhaps of more value, and affords a better idea of its purity and composition, than any of the foregoing methods of examination, and taken in conjunction with the solubility test, it will generally give the analyst a very fair idea of the composition of his sample.  If we regard gun-cotton as the hexa-nitro-cellulose, the theoretical amount of nitrogen required for the formula is 14.14 per cent., and in the same way for collodion-cotton, which consists of the lower nitrates, chiefly, however, of the penta-nitrate, the theoretical nitrogen is 12.75 per cent., so that if in a sample of nitro-cotton the nitrogen falls much lower than 14 per cent., it probably contains considerable quantities of the lower nitrates, and perhaps some non-nitrated cellulose as well (C_{6}H_{10}O_{5})_{x}, which of course would also lower the percentage of nitrogen.

The most expeditious method of determining the nitrogen in these nitro bodies is by the use of Lunge’s nitrometer (Fig. 41), and the best way of working the process is as follows:—­Weigh out with the greatest care 0.6 grm. of the previously dried substance in a small weighing bottle of about 15 c.c. capacity, and carefully add 10 c.c. of concentrated sulphuric acid from a pipette, and allow to stand until all the cotton is dissolved.  The nitrometer should be of a capacity 150 to 200 c.c., and should contain a bulb of 100 c.c. capacity at the top, and should be fitted with a Greiner and Friederich’s three-way tap.  When the nitro-cotton has entirely dissolved to a clear solution, raise the pressure tube of the nitrometer so as to bring the mercury in the measuring tube close up to the tap.  Open the