1822.) Scientific Intelligence. 71 
They are said to occur always in the form of rolled pebbles, and 
to constitute almost entirely the bed of the river called Sala 
grami. The specimens themselves are of that sort which the 
Hindoos worship under the name of Salagrams; the present 
kind being called Shesha Kundala. They consist of a very firm 
variety of a blackish argillaceous rock, and their form is that 
of ammonites in which they seem to have been moulded. 
ARTICLE XY. 
SCIENTIFIC INTELLIGENCE, AND NOTICES OF SUBJECTS 
CONNECTED WITH SCIENCE. 
I. Definition of a Straight Line. 
A correspondent states that he shall feel obliged by any objection to 
‘the following definition of a straight line : 
A straight line is such as being divided or produced to any extent, 
is still directed towards the same points. 
Il. Black Urine. 
It appears from Dr. Marcet’s paper in the Medico-Chirurgical 
‘Transactions, that he has met with somecases in which black urine had 
been voided. At the request of Dr. Marcet, some was examined 
by Dr. Prout, who gives the following account of its chemical pro- 
perties : 
The residuum obtained from this urine by evaporation not only does 
not contain any lithic acid, as was observed by Dr. Marcet, but no 
urea can be detected in it by the tests which indicates its presence. 
Although the addition of dilute acids produced no immediate 
change of colour in the urine, yet, on standing for some time, a black 
precipitate slowly subsided, leaving the supernatant fluid transparent, 
and but slightly coloured. 
The black precipitate thus obtained was found to be nearly insolu- 
luble either in water or alcohol, whether hot or cold. It readily dis- 
solved in cold concentrated sulphuric and nitric acid, forming a deep 
brownish-black solution; but, on diluting the acids with water, the 
black substance appeared to be again precipitated unaltered. These 
acids, however, by the assistance of heat, apparently decomposed it. 
The black substance readily dissolved in the fixed alkalies and in the 
alkaline subcarbonates, forming very dark solutions. The addition 
of water did not affect these solutions; but acids re-precipitated the 
substance apparently unchanged. When ammonia was employed as 
the solvent, and the excess expelled by evaporation to dryness, a black 
or deep brown residuum was obtained, which appeared to be a com- 
