Commercial organic analysis : a treatise on the properties, proximate analytical examination, and modes of assaying the various organic chemicals and products employed in the arts, manufactures, medicine, etc., with concise methods for the detection and determination of their impurities, adulterations, and products of decomposition / by Alfred H. Allen.

  • Allen, Alfred Henry, 1847-1904.
Date:
[1892?]-1898
Catalogue details

Licence: In copyright

Credit: Commercial organic analysis : a treatise on the properties, proximate analytical examination, and modes of assaying the various organic chemicals and products employed in the arts, manufactures, medicine, etc., with concise methods for the detection and determination of their impurities, adulterations, and products of decomposition / by Alfred H. Allen. Source: Wellcome Collection.

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    extremely faint reaction with the xanthoproteic test. The xantho- proteic reaction may he used for the approximate determination of peptone, and perhaps of albumin. Gelatin and gelatin-peptone yield no coloration with nitric acid, a fact which gives the xanthoproteic reaction an advantage over the biuret test, as in the latter case the shade as well as the intensity of the colour varies considerably. Liebermann’s colour-reaction with strong hydrochloric acid is not yielded by any of the decomposition-products named above. Pickering considers that the xanthoproteic and Millon’s re- actions are probably due to the presence of a hydroxybenzene nucleus in the proteid molecule, and that the reactions of Liebermann and Adamkiewitz depend on the aromatic portion of the molecule, while the brilliant red colour given with a solution of alloxan observed by Krasser probably depends on the presence of an amido-group. J. W. Pickering (abst. Jour. Ghem. Soc., 1893, i. 615) finds that cobalt salts with caustic alkali give distinctive colour- reactions with proteids. Native proteids give a heliotrope-purple, proteoses and peptones a red-brown. Gelatin, keratin, and various other organic substances related to proteids give similar colours. Gelatin gives a play of colours in the spectral order, as also do alloxan, allantoin, and biuret. Pickering thinks these reactions, as also those produced by nickel and copper salts, are due to the presence of the group CO.NH in the molecule. The precipitates produced in proteid solutions by mercuric chloride, silver nitrate, and sulpho-salicylic, phospho-tungstic, and phospho- molybdic acids yield the typical proteid colour-reactions. The nucleo-albumins behave like coagulable proteids, not as peptones, in their colour-reactions. C. Reichl (abst. Jour. Cliem. Soc., 1889,p. 1092; 1890,p. 1350) has described a number of colour-reactions obtained by treating proteids with an alcoholic solution of benzaldehyde or other aromatic aldehyde in presence of dilute sulphuric acid and ferric chloride. He concludes that the colours are due to the skatole- group in proteids. Coagulation of Proteids. In studying the proteids it is important to distinguish between mere precipitation and true coagulation. Thus, on saturating a neutral solution of any proteid but the peptones with ammonium sulphate, the proteid is precipitated perfectly, but will redissolve when the greater part of the precipitant has been removed by washing. On the other hand, a true coagulated proteid, as