292 Dr. Schunck on the Occurrence of Indigo-blue in Urine. 
acid, a product of the decomposition of indigo-blue, no further 
considerations were necessary to induce me to proceed with the 
investigation, notwithstanding the difficulties which I found at- 
tending it. Into the details of this investigation I shall at pre- 
sent only enter so far as they relate to the occurrence of indigo- 
blue in urine. 
When acetate of lead is added to ure, it produces a cream- 
coloured precipitate, which consists of chloride, sulphate, phos- 
phate, and urate of lead, and contains also a little of the extrac- 
tive matter of urine, which is, as it were, merely attached to 
some of these lead compounds, since it is not precipitated from 
its watery solution by acetate of lead, when in a state of purity. 
The filtered liquid, which is much paler in colour than it was 
before the addition of acetate of lead, gives with basic acetate of 
lead a second precipitate of a pale cream colour, which consists 
of the lead compound of the extractive. matter mixed with 
some basic chloride of lead. Both this and the first precipitate 
give, when treated with sulphuric or muriatic acid, yellow liquids, 
which, after being filtered from the sulphate or chloride of lead 
and boiled, yield brown fiocks exactly like those obtained from 
urine itself. The liquid filtered from the precipitate with basic 
acetate of lead is almost colourless. It gives, however, on the 
addition of ammonia, an almost white precipitate, the quantity of 
which is much less than that of either of the two other precipi- 
tates. Now this precipitate exhibits a very remarkable peculiarity. 
It contains in most instances in combination with oxide of 
lead, a small quantity of a substance which, by decomposition 
with acids, yields indigo-blue. The first time that I treated this 
precipitate with acid I was surprised to observe that the hquid 
became immediately of a purplish-blue colour, and deposited after 
filtering and standing a small quantity of a substance, which on 
examination was found to consist chiefly of indigo-blue. This 
phzenomenon was observed on so many occasions that I came to 
the conclusion that the occurrence in urine of an indigo-produ- 
cing body similar to indican, was by no means an unusual 
circumstance. 
In order to ascertain whether this body is present, I adopt 
the following method. The urine having been mixed with basic 
acetate of lead until no more precipitate is produced, is filtered, 
and after the precipitate has been washed with water, the liquid 
is mixed with an excess of ammonia, which always produces more 
or less of a white or yellowish-white precipitate. This precipi- 
tate is collected on a filter, slightly washed with water and then 
treated with dilute sulphuric or muriatic acid in the cold. 
After the whole of the oxide of lead has combined with the acid 
employed, the liquid is filtered, When there is much of the 
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