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.

  • Alfred Henry Allen
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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    obtained by boiling the solution, by prolonged treatment with alcohol or by the action of certain precipitants, cannot be re- dissolved by any method not involving chemical change. True coagulation of certain proteids is also produced by peculiar ferments, the curdling of milk by rennet and of blood when removed from the body being due to this cause. Heat Coagulation.—One of the most characteristic of the properties of albumin and other soluble proteids is that of under- going coagulation when their neutral solutions are heated. Thus the solution of white of egg in water becomes cloudy when heated to about 60° C., and on increasing the temperature to 72° or 73° the albumin coagulates and becomes wholly insoluble. The temperature at which the coagulation of proteids occurs is modified by the dilution of the liquid and the time taken to raise it to the coagulating point. Haycraft and Duggan maintain {Brit. Med. Jour., 1890, p. 167 ; abst. Pharm. Jour., [3], xx. 604) that Halliburton’s observation of the fractional coagulation of blood- serum does not prove the presence of several proteids of different coagulation-points, since the coagulation of part of the albumin would diminish the acidity and increase the dilution in which the remainder was left, necessitating for this a higher temperature for coagulation (compare page 42). According to A. Gautier, on coagulating 100 grammes of egg- albumin by heat, alkali is set free in quantity sufficient to neutralise 1‘53 gramme of H2S04. The purest albumin invariably yields about 0'5 per cent, of ash, which usually consists of calcium phosphate, sodium chloride, and sodium sulphate. Gautier con- siders it probable that these salts exist in the unaltered albumin as calcium chloride and sulphate, and as sodium phosphate {Bui. Soc. Chim., xliii. 596 ; abst. Jour. Chem. Soc., 1885, p. 1082). The coagulation of proteids by heat receives practical applica- tion in the use of albumin in calico-printing, and is one of the simplest and best tests for the presence of albumin, &c., in urine. The best method of applying the test is described on page 51. Alcohol Coagulation.—Alcohol, added in moderate quantity, precipitates albumins and globulins from solution in a form soluble in pure water; but if the alcohol be added in large excess, and the resultant precipitate be left for some time in contact with strong alcohol, true coagulated proteid is formed, indistinguishable from that produced by heat. Albumoses and peptones are pre- cipitated but not coagulated by such treatment (page 18). When employing the coagulation of proteids by alcohol for their gravimetric determination the liquid should be mixed with four times its measure of methylated spirit, and allowed to stand