The news and herald. (Winnsboro, S.C.) 1877-1900, 1880-01-10
SCIENTIFIC.

Engraving Copper Rollers.-Coppcr
printing-rollcrs are usually engraved
In two ways, one of which is the i'm
preston Of the pattern by means Of
steel die, q process which sometimes,
as In tho case OF heavy furniture pat
terms, is supplemented by direct engrav-
ing with craving tool by hand. The
other plan Is etching, the substance Of
tho copper being eaten away by the ap-
plication of acids. This process gives
nice shading, and when judiciously en-
ployed Is Of much use. Generally this
method consists IN covering tho roller
with mastic or varnish, which protects
the places which are not to be acted up
on, and which leaves the pattern to be
engraved open. The roller thus pre-
pared Is then plunged into a bath Of nj
tric acid of Is deg. or stronger. Some
times little hydro chlOric acid Is add
Cd to favor tho dissolving action Of the
acid. The operation generally takes
no moro than five or ten minntes. This
presses has grave Inconvenience, eS-
pecially in places where there is not Il
sufficiently strong ventilation to carry
OF ut once the fumes which arc formed
In large quantities. This free acid Is
not only dangerous for the workpeople,
but, spreading in tho room, soon affects
The machines. There is also this draw
back, that the acid acts underneath the
varnist, resulting In unclean edges OF
the engraving. A German chemist has
for some time employed chronic acid In
place Of nitric acid, and from all ac-
counts with very satisfactory results,
especially In damp localitios. The at
tack Of this acid upon the metal is lit
tie slower, but the engraving is sharper
and cleaner. Tho solution Is the fol-
lowing:-6 or. of commercial bichro.
mate of potash dissolved in 28 OF. Of hot
water, after which ID on Of sulphuric
acid Of &C deg. arc carefully added, and
The whole we'll mixed. This bath gets
brow u from usage; If after few days
is becomes much SO it must be thrown
away. 1t is necessary In order to OBJ;
tain COED results, to heat slightly the
bath, which is done by placing tho
trough containing 1t into bath Of tcp-
10 water. The cost Of working with
chromsc acid thus obtained Is said to
be cheaper than with nitric, and alto
gether 1t appears to have many features
10 recomend it to calico printers.
At the last meeting Of the French
Academy OF Science NJ. l.. Brault read
a memoir on two phases Of tho annual
circulation of the air. The study OF
barolnetric pressure over the entire
globe had led to two important results;
!. In summer the lowest pressures on
Tho continents are in tho northern hemi-
sphore, and the highest continental
pressurcs in the southern hemisphere:
IN winter, on tho contrary, tho lowest
continental pressufes arc in tho south
hemisphere, and tho highest In the
northern. Thus summer exists In the
IN
sures OF Central Asia and OF North
America, and the max imum pressures
OF South America, Australian and
Southern Africa are established. 2. On
tho whole surface Of the earth tho low
est continental prassures Of the summer
lnonths become in winter tho highest,
and. reciprocnlly. tho highest becomes
tho lowest. Between the two seasons
the pressure Is greatest In the North
Atlantic and South Pacific Oceans.
"A remarkable specimen Of siliside of
iron has been exhibited to the French
Academy Of Science. 1t was u piece of
lhg metal of about three Kilograms
weight, and of brilliant surface which
resists almost all ordinary chemical
agents. The color Of tho mass was
nearly the samo as that OF platinum,
and Its specific weight was about 80.
The reshlt, as given, of the investiEa-
tion to which the spec zen was submit.
ted. proved the metallic mass to be a
silicuretted iron, remarkably rich in
silicon, and that 1t was evidently the
product Of a blast furnace. The acci-
dental discovery Of this mass proves
that there can bo produced on a large
scale iron containing much larger
proportion Of silicon than has over been
produced in tho laboratcry-a fact of
much Importance In Il chemical and
metallurical point Of view.
1t Is now proposed to make railroad
ties OF glass. SO with car-w Of pa
per and ties OF glass we may soon ex-
psct rails Of putty or some such sub
stance. Soon after Dc Ia Bastic intro
duced his method OF toughening glass,