resulted in devising a method of making silver mirrors commercially.
One of the greatest troubles with which he had to contend was this
browning--the cause for which was never fully cleared up by him. Some
years ago, the writer, having in his possession two mirrors made by
Liebig, and which had gradually become brown throughout, undertook an
examination of the deposit (which had been thoroughly protected from
extraneous influences by a strong film of varnish), and was surprised
to find that it consisted of a layer of silver sulphide. Without going
into detail, the source of the change was later found to lie within
the glass itself. In making glass to be used for mirrors, a
considerable portion of sodium sulphate is used, and in annealing,
this is partly reduced to sodium sulphide, which effloresces on the
surface of the glass. This efflorescence is, of course, removed on
cleaning the glass before silvering; but it is found that, in many
instances, on exposure of the mirror to the light for some time, a
further efflorescence occurs, and it is this which produces the
discoloration in cases such as we have cited. It has been suggested
that the tendency to subsequent efflorescence may be corrected by
boiling the plates, intended for silvering, for a couple of minutes,
in a 10 per cent. solution of sodium carbonate or bicarbonate. We have
no experience with the process, however.--National Druggist.

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WILD AND DOMESTIC SHEEP IN THE BERLIN ZOOLOGICAL GARDEN.