PREFORM III) PIGMENTS OF NORMAL URINE. 619 
portion of the substance we axe now to describe, but they were mixed 
with urobilin and with decomposition products. 
To A. E. Garrod ' we owe a process for the extraction of the essential 
yellow colouring matter, which is beyond reproach in its avoidance of 
destructive reagents. It yields a product entitled to be considered, with 
a large degree of probability, as a chemical individual. 
Following Garrod, we shall describe this pigment under the name of 
urochrome — a name eminently fitted for a substance which is the prime 
cause of the familiar colour of urine, but in the use of which we must 
avoid historical confusion. 
Between the urochrome of Garrod and that described thirty years 
earlier there is the difference between presumptive chemical individual- 
ity and almost certain admixture. It should be stated, however, that 
Thudichum still holds the pigment described by him to be a definite 
sul tstance, and has recently investigated certain of its reactions, which he 
believes indicate for it the combined characters of an alcohol and a base. 
Sejxiration of urochrome (Garrod). — The urine is saturated with crystals 
of ammonium sulphate, and, after standing, is filtered (vide infra, " Separation of 
Urobilin"). The nitrate, which is still almost as highly coloured as the original 
urine, is shaken with alcohol. The latter solvent separates rapidly from the 
saline mixture, and is seen to withdraw a large proportion of the colouring 
matter. Eepeated extraction removes practically all. The alcoholic solution 
is diluted with a large bulk of water, and the mixture again saturated with 
ammonium sulphate ; by this procedure the alcohol is again made to separate 
from the water, carrying the pigment with it, and a satisfactory washing of 
the original extract is secured. This second alcoholic solution is now made 
just alkaline with ammonia, and evaporated to dryness ; the residue^ is 
extracted once or twice with acetic ether, which removes certain impurities, 
and is again dissolved in strong alcohol. Somewhat prolonged digestion is 
necessaryat this stage, as the solubility in alcohol is decreased when the 
pigment" has once been taken to dryness. Finally, the alcohol is concentrated 
till it has a deep orange colour, and is poured into at least an equal volume of 
ether, when an amorphous brown precipitate falls, consisting of the greater 
portion of the pigment present, in almost pure condition. The precipitate 
may be filtered off, dried on the paper, and washed with a little chloroform 
and absolute alcohol.' 2 
Properties. — The substance so prepared is a hygroscopic, brown, 
amorphous substance, easily soluble in water, much less soluble in 
alcohol ; only slightly soluble in acetic ether, amyl alcohol, or acetone ; 
and insoluble in chloroform, ether, and benzene. Its solutions show no 
definite spectroscopic absorption-bands, even after the addition of acids. 
Zinc chloride and ammonia produce no fluorescence. Alkalies give the 
solution a brownish tint, acids a reddish brown. The pigment forms 
insoluble compounds with the heavy metals, and is precipitated by 
phosphotungstic and phosphomolybdic acids. With strong nitric acid 
it undergoes a colour change resembling the xantho-proteic reaction. 
Urochrome we have seen to be a pigment which can be removed 
from the urine without the use of strong reagents, and in the removal 
of which the fluid loses nearly all its colour. At the same time, its acpueous 
1 1'roc. R011. Soc. London, 1894, vol. lv. p. 394. 
2 See also fcramm, Deutsche med. IFchnschr., Leipzig, 1896, Bd. xxii. S. 25 and 42. Tins 
author separates the pigment by an entirely different method. He confirms Garrod's 
original account of its properties. 
