1872.] Technology. 537 
process is very simple, but the details require much care and attention. Theend 
to be obtained is simply this : that the metal to be coated shall be ‘‘ chemically 
clean’? when immersed in the solution in which it is to be coated. There are 
several ways in which the attainment of this end may be prevented—by in- 
adequate means for cleansing; by a passage through the air of two or three 
feet after being cleansed; by the metal being positive in the coating solution 
—in this case the metal is fouledoncontacé. This refers to cyanide solutions, 
to sulphur and chloride solutions, to double sulphates and chlorides, as of 
nickel and ammonia, and of platinum and potash or soda. All of these may 
be used in certain cases for pyro-plating, but they are not used. There is a 
special solution used for pyro-plating in all cases, because most of these solu- 
tions leave matters on the metal that is being coated if it be in the slightest 
degree porous or ‘‘roaky,” as is the case with steel that has been badly 
faggoted, and on the article passing through the furnace these matters volatilise 
and cause an irruption in the coating. The amount of metal put on is ascer- 
tained by having a test-surface put in with the articles, and the exadé time of 
plating and the exact weight of the test noted. This test is carefully weighed 
from hour to hour until the amount desired is put on. After being dried, the 
articles are put into the furnace. The firing-furnace, as it is technically 
termed, is of simple construction. A bright red heat is required in the chamber 
where the articles are placed. In firing knife-blades and other cutting instru- 
ments, care has to be taken that the heat is not carried higher than 450° and 
500° F. This is ascertained by trials on a pad of prepared test-paper; a blade 
is taken out from time to time and tried upon the pad, and the colour noted 
—whether the blade scorches it straw-colour, yellow, pale brown, deep brown, 
or black. After the desired heat is attained, the blade is instantly immersed 
point downward in cold water, and all that were in the firing-chamber with it. 
The theory of the process, which is technically termed ‘‘ burning in,”’ is this :— 
On the instantaneous immersion in cold water, the coating is seized and 
retained by the suddenly contracting under metal. This is seen to be the case 
on filing or grinding the coating from the under metal ; for though the coating 
may be filed or ground off until both coating and under metal are filed or 
ground off together, yet the under metal remains spotted all over with an 
infinity of little points, the pores filled by the coating metal. 
TECHNOLOGY. 
An American engineer recommends the following composition as a cement 
for leather, wood, &c., resisting the action of water, both hot and cold, and 
most of the acids and alkalies. Three parts, by weight, of shellac, and one 
part of caoutchouc are to be dissolved, in separate vessels, in ether free from 
alcohol, applying a gentle heat. When thoroughly dissolved, the two solu- 
tions are to be mixed. If the glue be thinned by the admixture of ether, and 
applied as a varnish to leather, it renders a joint or seam water-tight. 
M. B. Renault has submitted to the Academy of Sciences a new method for 
obtaining the reproduction of designs. ‘The design is traced with gummed ink 
upon stiff glazed paper, over which fine brass or bronze powder is dusted. By 
this means a kind of plate is obtained, admitting of the most varied designs 
being taken off upon prepared paper. By softening the ink with vapour of 
alcohol, the metallic powder can be removed when spent by use. 
A method of testing petroleum and other inflammable fluids, and also of 
determining their specific gravity, has been patented in the United States. 
The apparatus consists of an upright glass cylinder supported in the top of a 
chamber formed in the upper part of a base or stand. A lamp is placed in the 
base, the heat from which is transmitted through the chamber to the lower 
part of the glass cylinder, and the chamber may be made to contain air, water, 
&c., as required to regulate its intensity. The glass cylinder contains a ther- 
mometer, which is fixed therein, and is closed at the top with a brass cover. 
The fluid to be tested is made to completely fill the glass cylinder, so that the 
thermometer is entirely submerged and cannot be affected by the surrounding 
atmosphere. An orifice in the brass cover is opened, to allow the escape of 
vapour from the fluid under test, and when necessary the lamp is lighted. 
VOL. I. (N.S.) 32 
