r
or frosted etching is desired, the etching liquid is modified, being,
for the latter purpose, composed of 500 parts of ammonium fluoride,
100 of common salt, 300 of fuming hydrofluoric acid and 30 of ammonia.
This is brushed over the glass two or three times, and then rinsed off
with lukewarm water. For deep etching, hydrofluoric acid is diluted
with 11/2 vols. of water and stored for twenty-four hours before use.
The objects are immersed in the baths for thirty to fifty minutes, and
kept quite still the while. If the etching is to be left clear, the
acid is neutralized by boiling the glass in soda, but if to be frosted
afterward it is coated with the first named etching liquid while still
damp. Finally, the ink is washed off with turpentine, the glass rubbed
over with sawdust, washed in hot lye and rinsed with water.

Grained or lined designs can be very suitably printed from a litho
stone, on paper faced with a mixture of 1,500 parts of water, 250 of
wheaten starch, 1,000 of glycerine and 200 of a thick solution of gum
arabic, the ink for printing being prepared by melting and mixing 500
parts of pure tallow, 250 of white beeswax, 250 of liquid mastic, and
150 of pale resin, with 100 parts of lampblack, 5 of minium, and 500
of litho varnish. In transferring the design to the glass, the latter,
if flat, may be passed between India rubber rollers or protected by
layers of gutta percha when the pressure is applied. The impression
produced by this lithographic process has to be strengthened to enable
the thin coating of ink to resist the etching liquid, and this is done
by dusting powdered resin over the printed surface of the glass,
brushing off all that does not adhere, and causing the remainder to
attach itself to the ink by means of warmth, and so form an impervious
covering. The further treatment is the same as that already described.
These methods are particularly suitable for reproducing landscapes,
etc., on thinly flashed glass of various colors.--Diamant.

* * * * *

SLATE AND ITS APPLICATIONS.

Slate is, as we know, merely a variety of argillite. Slate quarries
are found in England, Switzerland and Italy, but it is in France
especially that the industry has been most extensively developed by
reason of the large deposits that underlie its surface, particularly
in the province of Anjou, where they extend from Trelaze to Avrille, a
distance of six miles, and in the depar