154 
ON A NEW TEST FOR UREA. 
belongs to the siccative oils. Ether extracts, besides the oil, 
another more resinous digitaline compound, which sinks in water, 
while the oil floats on the top. A portion of the digitaline com- 
pound can be removed from the oil by water. 
The tannate of digitaline is soluble in hot water; on cooling, it 
again separates for the greater part. 
Digitaline prevents the fermentation of an aqueous solution of 
sugar; it must therefore be considered as a poison to beer-yeast. — 
Chem. Gaz.from Buchner's Repert. 
ON A NEW TEST FOR UREA. 
By Professor Liebig. 
When a solution of pure urea is rendered strongly alkaline 
with solution of caustic potash, a solution of corrosive sublimate 
added to it by degrees, a dazzling white precipitate — a combina- 
tion of the peroxide of mercury with urea — is obtained. 
As is well known, a dilute aqueous solution of corrosive subli- 
mate may be mixed with an excess of a solution of bicarbonate 
of potash without the immediate production of a precipitate ; if 
a solution of urea be added to this mixture, the above-mentioned 
white precipitate of urea and peroxide of mercury is immediately 
formed. This compound is so little soluble in water, that by 
this process l-5000th urea can be detected with certainty in a 
liquid. The whole of the urea can be precipitated from urine by 
this means, and its application to the quantitative determination 
of urea in animal fluids is evident. I shall take an early oppor- 
tunity of describing a suitable method for this purpose. 
When oxide of silver (recently precipitated is best) is placed in 
an aqueous solution of urea, it is converted, in the course of a 
few hours, more quickly when gently heated, into a gray or yel- 
lowish-gray granular powder, which appears under the micro- 
scope to consist of transparent crystals. This compound when 
dry gives off ammonia when heated, leaving cyanate of silver, 
which burns at a higher temperature into sesquicyanide of silver, 
and finally into pure silver. — Chem. Gaz. from Idebig's Anna- 
len, Oct., 1851. 
