12. _Diphenylamine sulphate._--A solution of the base in concentrated sulphuric acid colours the natural silks a brown; the collodion 'silks' give a strong blue reaction due to the presence of residual nitro-groups. The Pauly product is not affected. 13. _Brucin sulphate_ in presence of concentrated sulphuric acid colours the natural silks only slightly (brown); the collodion 'silks' give a strong red colouration. The Pauly product again is without reaction. 14. _Water._--The natural silks do not soften in the mouth as do the lustra-celluloses. 15. _Water of condition_ was determined by drying at 100 deg.; the following percentages resulted (a). The percentages of water (b) taken up from the atmosphere after forty-three hours' exposure were: (a) (b) China (raw) silk 7.97 2.24 Tussah silk 8.26 5.00 Lustra-celluloses: Chardonnet (Besancon) 10.37 5.64 " Spreitenbach 11.17 5.77 Lehner 10.71 5.97 Pauly 10.04 6.94 16. _Behaviour on heating at 200 deg.._--After two hours' heating at this temperature the following changes were noted: China silk Much discoloured (brown). Tussah silk Scarcely affected. Lustra-celluloses: Chardonnet Converted into a blue-black charcoal, retaining the Lehner form ofthe fibres. Pauly A bright yellow-brown colouration, without carbonisation. 17. The _losses of weight_ accompanying these changes and calculated per 100 parts of fibre dried at 100 deg. were: China silk 3.18 Tussah silk 2.95 Lustra-celluloses: Chardonnet 33.70 Lehner 26.56 Pauly 1.61 18. _Inorganic constituents._--Determinations of the total ash gave for the first five of the above, numbers varying from 1.0 to 1.7 p.ct. The only noteworthy point in the comparison was the exceptionally small ash of the Pauly product, viz. 0.096 p.ct. 19. _Total nitrogen._--The natural silks contain the 16-17 p.ct. N characteristic of the proteids. The lustra-celluloses contain 0.05-0.15 p.ct. N which in those spun from collodion is present in the form of nitric groups. The points of chemical differentiation which are established by the above scheme of comparative investigation are summed up in tabular form. _Methods of dyeing._--The lustra-celluloses are briefly discussed. The specific relationship of these forms of cellulose to the colouring matters are in the main those of cotton, but they manifest in the dye-bath the somewhat intensified attraction which characterises mercerised cotton, or more generally the cellulose hydrates. _Industrial applications_ of the lustra-celluloses are briefly noticed in the concluding section of the book. FOOTNOTES: