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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    elsewhere, and one well known to Jaffe, that very dilute solutions of urobilin are distinctly pink in colour, and we can assert at any rate that in repeating Esoff's observation, the pinkish ethereal extracts sometimes obtained have always shown a band at F proportionate to the amount of colour present. There are many difficulties connected with the zinc chloride separation, some of which are referred to below, but we venture to repeat our conviction that Jaff^ obtained an excellent product by its means, and that his descriptions, so far as they go, apply exactly to the properties of the pure pigment. Ten years after Jaffes discovery of the pigment, Mdhu^ made the important observation that urobilin could be precipitated from urine, to which a little sulphuric acid had been added, by saturation with crystals of ammonium sulphate. From the precipitate thus produced he isolated the pigment by extraction with absolute alcohol, rendered alkaline with ammonia, the alcoholic extract being afterwards evaporated to dryness at a low temperature. This method has since been employed by many observers, not only for the separation of urobilin, but also for the estimation of its quantity. Minor modifications have sometimes been introduced in the final stages, but an efficient fractionation of the product has never been secured. We shall have occasion, immediately, to discuss this process further, and it is also dealt with in a later section of this paper. To avoid repetition we will here only state our belief that the ammonium sulphate separation, although a most valuable one, has never yet been so used as to yield a product even approximately pure. We may note in this place the important observation of Eichholz that the chromogen of urobilin is also precipitated by ammonium sulphate, and may be obtained from urines in which it is present by using Mehu's method without preliminary acidification with sulphuric acid. The only other methods of importance which have been used for the separation of urobilin are based upon precipitation with the acetates of lead. MacMunn precipitates the urine with both acetates, and treats the mixed precipitates with alcohol containing sulphuric acid. The solution filtered from lead sulphate is largely diluted with water, and shaken with chloroform. The latter is then evaporated to dryness, and the residue redissolved in alcohol or a second time in chloroform, 1 Dull, de I'Acad. de M6d. [2] vii. p. 671. 1878. 2 Cf. G. Hoppe-Seyler. Viichow's Archiv, cxxiv. p. 30.