228 Chemical Analyses. 
M. Vogel has analysed the brick-dust sediment of the human 
urine, known by the appellation of the rosacic acid. This substance 
has not been found in the urine of a healthy person by M. Vogel, 
although M. Proust was of a contrary opinion. The former 
observes :— | never found that this red substance was formed 
previous to or during the state of fever ; it always began to make 
its appearance at the period when the crisis was completely past. 
Recently I had an opportunity of procuring a considerable quan- 
tity of this substance. A friend who is subject to gouty attacks 
voided this kind of urine during fifteen days, and collected the 
red powder for me by filtration. Cold water has no effect on 
it, but boiling water dissolves it completely. The solution is 
brownish ; aud as it cools, a white powder is deposited. The 
liquid has a smell like that of urine, and reddens turnsole tine- 
ture. 
‘* Boiling alcohol of the specific gravity of 40° in Baumé’s are- 
ometer, dissolves it sensibly, but not so completely as boiling 
water. By decanting off the alcohol, and boiling the residue se- 
veral times with a new quantity of alcohol, this liquid finishes 
by being perfectly colourless, and there remains a mueh paler 
powder, and upon which alcohol seems no longer to act. After 
being dried, this powder is almost white. It forms a strong 
froth with cold nitric acid ; and when the mixture is evaporated 
to dryness, red soft scales remain, as is the case when uric acid 
is heated by nitric acid. The alcohol saturated with this red 
matter was evaporated to dryness, and a red powder remained 
unalterable in the air, which I consider as pure rosacic acid, 
and from which the uric acid has been separated by the aleohc!. 
On the rosacie acid thus purified I made the following experi- 
ments :—It was completely dissolved in water: the aqueous 
solution reddens turnsole tincture, without however disturb- 
ing lime-water ; which proves that no phosphoric acid is pre- 
sent. 
“* The rosacic acid dissolves without effervescence in concei- 
trated sulphuric acid. A red liquor is produced, which gradu- 
ally becomes darker. This liquid loses its colour on the addi- 
tion of a little water, and a white powder is precipitated. The 
same white sediment is produced by alcohol. The white powder 
is almost insoluble in water, when it is washed until all the sul- 
phuric acid is taken from it. It presents all the characteristics 
of uric acid. When we sprinkle the rosacic acid with a few 
drops of sulphuric acid, the powder acquires a fine red colour ; 
but it soon becomes white, and in this state it resembles the 
uric acid, 
‘€ The liquid sulphurous acid in which we shake the pulveru- 
lent acid acquires a very lively rcd; a shade which it preserves 
2 Jong 
etn op a 
