each etching the plate
is thoroughly inked, and that this ink is melted down the sides of the
line, so as to protect the sides as well as the top from the action of
the acid; were this neglected, the acid would soon eat out the lines
from below. The greatest skill and care is, therefore, necessary in
this work, especially so in the case of some of the exquisitely fine
blocks which are etched for some art publications.

There are many details which are necessary to successful etching, but
those now given will be sufficient to convey to you generally the
method of making the zinc plate for the typographic block. After
etching there only remains the trimming of the zinc, a little touching
up, and mounting it on a block of mahogany or cherry of exact
thickness to render it type high, and it is now ready for insertion
with type in the printer's form. From a properly etched plate hundreds
of thousands of prints may be obtained, or it may be electrotyped or
stereotyped and multiplied indefinitely.--_G.S. Waterlow, Brit. Jour.
Photo._

* * * * *

ANALYSIS OF A HAND FIRE GRENADE.

By CHAS. CATLETT and R.C. PRICE.

The analyses of several of these "fire extinguishers" have been
published, showing that they are composed essentially of an aqueous
solution of one or more of the following bodies; sodium, potassium,
ammonium, and calcium chlorides and sulphates, and in small amount
borax and sodium acetate; while their power of extinguishing fire is
but three or fourfold that of water.

One of these grenades of a popular brand of which I have not found an
analysis was examined by Mr. Catlett with the following results: The
blue corked flask was so open as to show that it contained no gas
under pressure, and upon warming its contents, but 4 or 5 cubic inches
of a gas were given off. The grenade contained about 600 c.c. of a
neutral solution, which gave on analysis:

In 1000 c.c. In the Flask.
Grammes. Grains.
Calcium chloride