The sun., 1896-08-16
NOTES ON SCIENCE AND INDUSTRY.

strength Is said TO be % per cent. greater than
the best gclatine dynamite aud. In consequence vf
tho large volume OF gas which II produces--being
approximately double that yielded by dynamite
II has n wcdgng rather than pulNcriLinR action,
resulting in n materially increased fall OF lump
coal. other advantages mentioned TINS -
can be compressed without losing nuy OF the ex-
posivo force, and in this state Ia claimed even
exceed dynamite. A weaker detonator Ia ro.
Qured to bring It to explosion than is demanded
for any other known safety explosive. and II 10
better able Withstand the effects OF storage, and
no decomposition can take place when the packing
is proper. Indeed, such Is the safety with which
It may be handled that tho German railways allow
1t to be carried on any train.
There are said 70 be Michigan white cedar shin.
giles doing good service roofs in that STATE
that have becu in full exposure and wear for over
seventy Ave years II Is thus that climate AZ.
fects the durability OF shingles and the fact that
white cedar Is the natural product of Michigan
and red cedar OF the Pacific coast IA held TO be
proof that the red cedar is naturally adapted for
use the Pacinc coast and tho white for use in
such sections tho middle and Northwestern
States. &C. peculiar objection is brought against
the red cedar b; some namely, that there exists
In that wood acid which is, In the climate OF
certain sections 10 acted upon by water as to
corrode rapidly the nails with which the shingles
fastened onto roofs, the rust extending to the
wood around the nails. and soon causing leafy
roof-thfs action explaining the holes so often 10
be seen around the nails In red cedar roofs. An
other point offered for consideration in this con.
nection is the fact, stated that shingle 10
ruined by kiln drying, and that no kiln-dried lum-
ber bo regarded OF equal value for outAds
work to that which is air.dried.
Some sensitiEed Photographic metal plates OF
special value, tho work OF Mr. Strauss Collin, arc
noticed at length by the London Lancet. They
said to be developed in the ordinary way, us
ing "rodinnl" preferably as a developer, and, fxed
In the hyposuphite BATH very thorough washing
is tho next step and the image which first appears
on developing vanlshes In the hyposulphtc solu-
tion When, however, the plate, after washing,
is placed In solution OF perchIoride OF mercury,
the Image rcappears with great distinctncss and
with excellent detail, presenting special advan-
taHes for medical work Thus. the thin shccting
upon which the senstized flm Ia spread may bo
adapted to any shape, and unlike glass plates, IL
not easily fractured, 40 that II may bc placed un-
der the body OF patient without risk or breaking.
Moreover. as 1, apparent from the above named
process of development, n positive not unlike .
ferrotypo is at once obtalred- The tones good
and the plates fairly rapid.
The corrosive power OF puro water
unscalcd boilers well illustrated In the city OF
Glasgow, when supply intro
duced from Loeb Kntrine, one Of the purest waters
In the world which available for city
sumption. The former supply had been poor and
calcareous. and old boilers were much coated with
lime scale. To the dismay OF the users, those who
had put in boilers new tubes found them
rapidly corruding, while the old scaled ana coated
boilers remained as before: those, too who had
moved every possible trace of old incrustation
from their Old boilers by mechanical or chemical
means, intending thus TO get, they expected.
the full benefit Of the pure water, were also badly
troubled by co-rosion; and even the old boilers, as
scale gradually removed by the unvary-
insly soft aud pure water from the lake, more
or less corroded when no means were taken to pre-
It. 1t was found, however. in this case, that
Introducing little lime from time to tne-enough
to give the boilers a slight calcareous coating
usually prevented the corrosive action OF tho
water them again, in the course OF time. the effect
produced that the lime, organic matter, ard
oxide skin, united In forming protective OK
dizcd surface which prevented further corrosion.
process has been brought forward in Sweden,
by Ohm and Loftrand, for extracting gold or bis
muth from ores bv means of melted lead; the pro-
he applied TO mineral mixtures contain
ing. for example, iron ores limestone. bismuth,
native gold quarz, or sllicates, aud even when
the mixtures poor in gold ana bisnuth thas
1t would otherwise he Improbable TO work them
The method now brought forward consists In piae-
ing the In a bath OF melted lead. keeping It
free as possible from any contact with the air. To
gold which contain little bismuth, enough
OF the latter substance is added reduce the melt
Ing point or the alloy lar as porsiDe, In way
preventing oxidation OF the alloy and loss OF metal
which would otherwise result. The bath mado
OF for this purpose is filtered through a cyltn-
der, the bottom OF which consists of perforated
sheet OF metal covered with layer OF asbestos,
pieces OF iron wire, and coal dust
According to Prof. Patterson OF the Coast Survey,
the reason why the needle points In q northerIy
direction is because the earth In itself is magnet,
attracting the magnetic reede as the ordinary
magnets do, the earth being also magnet ns the
result OF certain cosmical facts, much affected by
the action of the These laws have periodci-
ties, all OF which have not as yet been determined.
A condensed explanation accepted In regard to the
needle pointing 10 the northward and southward
Is that The magne c poles of the earth do not coin
eide with the geographical polcs-that is. the axis
OF rotation makcr angle OF about twenty three
degrees with line Joining tho former. and hence
tho needle does not everywhere point to the
nomcal north, and is constantly variable within
certain limits; thus, at the northern magnetic pole,
u balanced needle pointr with It's north end down
ward In a plumb line, while at San Francisco 10
dips about sixty three degrees, and at the south
ern magnetic pole tho south end points directly
down. The action OF the eFrth upon magnetic
nced!r at its surface is OF about the force
tfat OF a nard steel magnet forty inches long and
strongly magnetized at a distance OF foot.
No ultimate reason can be given OF the fact in
ture that the ueedl" points to tfe northward and
southwark
In casting aiuminum bronze 4 special point OF
attention consists In not hea Ing ths metal too high
or the aluminium will oxdize, so tfat the alumni
ma thus formed mix with the metal ard make
the casting dirty" Tho metal Is also liable TO 10
spongy from the presence OF occluded Sases II the
scum which floats top OF the bronze in a melted
crucibe goes into the metal trouble arises the pre-
vention OF this being accomplished by the use q
suitable gates. Another point OF special consider
In thega he
metaI--one OF tho greatest troubles, in fact, at
tending the-process OF making aluminium bronze
! castings, which formerly seemed insurmount-
| able II is, however. overcome by giving the cast
ing large sinking head ana ''r!sers, though It 10
! often required to make tho sinking head as large
| as the casting.
| The Advantage OF Not BeinG . ThespiaA-