covered and heated for from fifteen to twenty minutes over the
blow-pipe, the lid being occasionally removed. The residue is soon
converted into ash, which is weighed, and then washed out into a porcelain
basin and treated with hydrochloric acid heated to 90 deg. C. The oxide of
iron, alumina, lime, and magnesia are thus dissolved, and the silica
remains as insoluble residue. The rest of the analysis is conducted
according to the well-known methods of separation. The percentage of ash
as a whole is generally all that is required.

~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 lowe