1819.] Philosophical Transactions for 1818, Part II. 308 
structed a catalogue of the fixed stars, and Mr. Pond has done 
the same in quite a different way. Yet the position of the stars 
in the two catalogues coincides within a small fraction of a 
second. 
VILL. A Description of the Teeth of the Delphinus Gangeticus. 
By Sir Everard Home, Bart. V.P.R.S.—The Delphinus gange- 
ticus was described by the late Dr. Roxburgh in the seventh 
volume of the Asiatic Researches, published in 1781. It is 
noticed by Dr. Shaw in the second volume of his General 
Zoology, published in 1801; but so inaccurately, that the 
description seems rather to apply to another animal. The author 
of this paper got a specimen of the upper and lower jaw of this 
animal from Sir Joseph Banks 17 years ago, which has been 
deposited ever since in the Hunterian collection. But it was 
only the other day that he discovered by an accidental reference 
to the Asiatic Researches the name of the animal to which the 
jaws belonged. He gives a figure of these jaws, and a short 
description of the teeth. They are 120 in number, 30 in each 
jaw. The upper part of the tooth, which is covered with 
enamel, has the figure of the point of a flattened cone. The 
under part is destitute of enamel, spreads out, increasing consi- 
derably, in breadth, but not in thickness, till itis at last imbedded 
in the substance of the jaw itself. 
IX. Description of an acid Principle prepared from the Lithic 
or Uric Acid. By William Prout, M.D.—The author has ascer- 
tained that the beautiful pink substance formed when uric acid 
is heated with nitric acid is a compound of a peculiar acid, to 
which Dr. Wollaston gave the name of purpuric, and ammonia. 
{t may be formed by dissolving uric acid in dilute nitric acid. The 
excess of nitric acid is then to be saturated with ammonia, and 
the whole slowly concentrated by evaporation. As the evapo- 
ration proceeds, the colour of the liquid becomes a deeper purple, 
and dark red granular crystals soon begin to separate in abund- 
ance. These crystals are dissolved in caustic potash, and heat 
applied till the red colour entirely disappears. The alkaline 
solution is then gradually dropped into dilute sulphuric acid, 
which uniting with the potash, the acid is deposited in a state of 
purity. Uric acid is likewise converted into purpurate of 
ammonia by chlorine and iodine. 
Purpuric acid has a slightly yellow or cream colour. It has 
no smell or taste. Its specific gravity is considerably higher 
than that of water. It is scarcely soluble in water; that liquid 
not being capable of dissolving -1.,,th of its weight of purpuric 
acid. It is insoluble in alcohol and ether. It dissolves in the 
concentrated mineral acids, and in the alkaline solutions it dis- 
solves readily. But it is insoluble in dilute sulphuric, muriatic, 
and phosphoric acids, and likewise in oxalic, citric, and tartaric ' 
acids. Nitric acid dissolves it with effervescence, and converts 
it into purpurate of ammonia. It does not attract moisture from 
