On urobilin / by Archibald E. Garrod and F. Gowland Hopkins.

  • Garrod, Archibald E. (Archibald Edward), Sir, 1857-1936.
Date:
[1896]
Catalogue details

Licence: Public Domain Mark

Credit: On urobilin / by Archibald E. Garrod and F. Gowland Hopkins. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    more slowly and in a less pure condition. With the urate are asso- ciated not only urobilin and its chromogen, but other pigments and chromogens also*. Even when the urine is first feebly acidified, as in Mehu's process, the precipitate is still largely composed of am- monium urate; the chromogens are decomposed, but other pigments are precipitated in addition to urobilin. Investigation shows that some at least of these pigments depend for their precipitation upon association with the urates and are not thrown down when these latter are absent, whereas for urobilin itself ammonium sulphate is a true precipitant. The behaviour of ammonium chloride is strikingly different, for urobilin is not precipitated at all by excess of this salt. When large quantities of the pigment are present some may be carried down mechanically with the urates, but there is no true precipitation. If therefore the urates be first thrown down by saturation with ammonium chloride and filtered off, and if crystals of the sulphate be added to the filtrate, a precipitate of ui'obilin is obtained on standing, which is much purer than the product of Mehu's process. It should next be noted that water, although by no means an active solvent of urobilin, takes up this substance much more readily than it does most of the other urinary pigments. If therefore the precipitate yielded by ammonium sulphate, after previous removal of the urates, be dried upon the filter-paper, and then extracted with distilled water (a large proportionate bulk of the solvent being necessary), the latter takes up the urobilin, and effects a further fractionation of the product. The aqueous solution is now again saturated with ammonium sulphate and the precipitate will consist of urobilin not very far from a state of purity. Such precipitation with the salt and re-solution in water may of course be repeated as often as is thought necessary; the final precipitate is dried and the pigment is extracted with absolute alcohol. When plenty of material is available the final stage should be carried out as follows. The product of the second or third pre- cipitation with ammonium sulphate is dissolved, no longer in pure water, but in dilute ammonia. Whereas a large bulk of neutral water was requisite for solution, in the alkali the urobilin is very freely soluble, and a quantity only just sufficient to dissolve the precipitate is employed, by which means a very concentrated solution is obtained. ' Cf. M6hu, Jour, Pharm. [5]. vii. 122; and Micbailoff, Joxir. Chem. Soc, liv, 880.