_Glass Baths._--Several of your correspondents finding a difficulty in
making glass baths, I beg to communicate the way in which they may be very
easily manufactured. Having obtained two pieces of patent plate glass,
grind the edges, which may readily be done by a scythe sand-stone, where
other contrivances are not handy. Cut for the bottom of the bath a slip of
the same glass three-quarters of an inch in breadth; and for the sides,
from ordinary window-glass, four wedges, being about three-fifths of an
inch at one end, tapering down to the thickness of the piece of plate glass
at the bottom. If several pieces are cut off promiscuously, four may be
selected which have exactly the same angle, so as to form an even support
to the sides. The glass being perfectly clean, dry, and as warm as can be
conveniently held by the hand, fix the bottom and then the sides by means
of the _very best_ sealing-wax, which will perfectly adhere to the glass.
If the commoner sorts of wax are used, some marine glue must be added to it
to temper it. The side slips should be fixed a quarter of an inch apart, so
as to form a cavity, which must be entirely filled up with wax. The wax may
be used as in sealing a letter in the first instance; but, in order to give
the whole bath solidity, and expel every particle of air from between the
glass, I use a heated pointed iron, as a plumber does in the act of
soldering. This, passed over the external parts of the wax, also gives it a
hardness and smooth finish.
These details may appeal trifling, and others may have more ingenious modes
of accomplishing the object; but having used baths so constructed upwards
of twelve months without leakage, I believe they will be found to be most
economical, and far more to be relied on than gutta percha. A good bath so
made should require about six ounces of solution of nitrate of silver to
take a picture eight inches square. Your observations in a former Number,
respecting the uncertainty of gutta percha, I have found to be perfectly
true. Samples of gutta percha constantly vary; and one may contain
impurities acted upon by the chemicals, which another does not. A small rim
formed by sealing-wax dissolved in spirits of wine, and applied twice or
thrice along the upper edge of the bath, is sufficient to protect the
prepared glass from adhering to the front of the bath when in use.