A Manual of the Chemistry of the Carbon Compounds

THM CARBON COMPOUNDS. 249
most conveniently prepared from guanine. Potassium nitrite is added
to a solution of guanine in nitric acid, until copious red fumes are
evolved. On adding water to the solution a precipitate consisting of
xanthine and nitioxanthine is formed, which latter compound is converted
into xanthine hy reducing it with a ferrous salt.
Xanthine is a white amorphous powder, and sparingly soluble in
water. It combines with acids, forming crystallized salts, and also
readily dissolves in alkalis. Oil adding silver nitrate to its aqueous
solution, a white gelatinous precipitate of silver-xanthine CsH^Np^Agg
+ H2O is obtained. By acting with methyl iodide on this body, it is
converted into dvmthyl-oamthine Qfi^CB^^fi^ which is isomeric
with tlieobromine.
Xanthine dissolves in fuming nitric acid without evolution of a gas.
On evaporating this solution a yellow residue is left behind, which on
addition of potash-solution assumes a yellow-red colour, which on
evaporation changes into violet.
iSmcvM or Hyjmanthiw occurs in the flesh of vertebrata, and forma
a white crystalline powder which is very sparingly soluble in cold
water, and unites with bases and acids. Its solution in nitric acid
leaves on evaporation a colourless residue, which is not changed by
caustic potash.
Ghiaiwie occurs in Peruvian guano, in the excrements of spiders,
aud the pancreatic juice of mammalia. In the so-called guanine-gout
of pigs, it is found deposited in the muscles of these animals. To
prepare it, guano is boiled with milk of lime, the solution filtered
aud precipitated with acetic acid. The precipitate, consisting of
guanine and urio acid, is dissolved in hot hydrochloric acid, and the
guanine precipitated with ammonia.
Guanine is a colourless crystalline powder, which is insoluble in
water, alcohol, ammonia, but soluble in acids and potash-solution, It
is a bi-acid base, forming two series of salts.
When guanine ia heated witb potassium chlorate and hydrochloric
acid, it is oxidized to gitanidine (see page 103), parabaoic acid, and
carbon dioxide:—
C5H5BT5O + O3 + HSO = CH6K8 + C$TA