and the birch. The leaves of the arbutus, employed in the governments
of Kasan, Viatka, and Perm, contain about 16 per cent. of tannin,
while the root of wild sorrel (_Rumex acetosella_) contains 12 per
cent. For removing the hair from hides, a lye made from wood ashes is
still employed. The softening of the leather is effected by means of
the excrement of dogs, which acts on the leather by means of the
biliary acid present, which forms with soda a kind of soap. After
tanning, white Russia leather is coated with a mixture of tar and seal
oil. Black Russia leather is dyed with alum, extract of sanders, and
ferrous sulphate. Horse hides are tanned to a great extent for sole
leather.--_M. Ryloff._

* * * * *




IMPURITIES IN PHOTOGRAPHIC CHEMICALS, AND TESTS FOR SAME.


[Table referred to in a paper read before the Birmingham Photographic
Society by G.M. JONES, M.P.S.]

------------------+---------------------+----------------------------------
SUBSTANCE | IMPURITIES | TESTS.
| POSSIBLY PRESENT. |
------------------+---------------------+----------------------------------
Ammonia, | Carbonic acid | Renders lime-water milky.
NH_{3} | |
Molec. Wt. 17 | Dissolved solid | Residue left on evaporation.