New-York tribune., 1872-02-12
SCIENTIFIC NOTES.

PREPARATION OF DEXTRINE.-O. Flcinus has
described, in Din0ier's Poyeeh"ie Journal a cheap
mode of preparing pure dextine. mixture. consisting
nj 200 parts OF potatosarch parts of cold distilled
water and eight parts OF pure oSae aid = placed IN
sample with iodine solution dees not produce ts
vessel is Immediately removed from the ~ and
havng been left standing couple OF days the liquor
Is filtered, and the clear hrate eyapored upon water,
bath until the becomes paste which is removed
by spaula and, having been made into tln cake -
placed upon paper and further dried IN warm pice
Two hundred and twenty parts OF pure de1trne are
thus obtained.
New Form OF SENSITIVE FLAME.-llr Philip
Barry of Cork, Ireland has devised new method Of
making sensitive flame, OF which he writes to Prot.
Tyndall follows II Is in my experience the most se-
sitive OF all sensitive flames. though from its sma"r
size il is not striking your vowel fame" IL pos
sesses the advantage that the ordinary pressure the
gas mains quite. sufficient develop it. The method
OF producing consists in iSning the tordndry coal
gas) the burner. but some inches above It, by in
terposing piece Of wire gauze between the burner
and the flame. The piece OF wire gauze 52 mesnes o io
incl is supported about inches above the buru
on turning the aud lighting II above the gauze
hame is obtained the shape Of slender cone four
inches high. the upper portion giving bright yellow
light the base being non-ulninous blue hane Al the
least noise this fame rOdTs, NJ the same time h1tHns
itself upon the gauze and becoming almost Invisible u
very active in Its responses and being rather noisy
t6 distinguish the vowel sounds 50 well as the vowet
flame proper To II Is extremely senSitye less 50 10
+ hut slightly sensitive To and u, and . has no lnni-
ence upon il whatever. To the sounds coming from
small musc-box IT dances in the most perfect manner:
/ which affect otker flames.
A SPIRAL LEYDEN JAR.-Mr. Frederick
Guthrie in note 10 Philosophical Hrga:ne LondonD
thus describes its construction: strip OF tnon four
feet long and eight ncheswde il placed upon strip oil
vucanzed caoutchouc four feet long and foot wlds
in such way that along both sides there Is margin of
two inches csoutchoue and at the left margin of fonr
inches OF tin second piece of caouchouc exactly
similar the first IL placed exactly over the nrst upon
the foil secondipeceof tin-fol Of the same width as
the first four inches shorter placed on the second
caoutehouc above the first foil, with its rlghhand end
above the right end OF the first foil Its left end, OF
course falls four inches short brass wre carrying
knob Is laid across the end OF the upper foil The whole
il rolled I'D from the right end and bound What was
the lower two fOs projects between the two lay
ers of caouchouc and be prolonged around the cir
conference OF the roll: il forms the outer coating or
What the upper coating OF foil now
forms what corresponds TO the inner coating OF the Ord
nary lar and entirely covered. excepting where II IL
prolonged as the and knob at the Of the roll
i sheet caoutchOuc DE eighth OF an inch n thick
ness lar OF very great electrical capacity Il obtained in
very compact form, and one which Is ree from the rsk
OF fracture and ess impaired than the ordinary ar ny
atmospheric moisture. very serveesble modification
OF this been constructed by using for the nsu
atng material sheet eDOnlte Inc ehds Oh tue spal ron
are capped with dry mahogany disks The earthfoh IA
with brass girde around the center OF the
cylinder and IL not visible The electric capacity be-
and FIVE times great a. that of glass Jar
OF the same volume IL has been In use for several
months and appears almost Incapable OF injury.
PERMANENCE OF SILVER PRINTs.-Mr. NJ.
Carey Lea in a communication TO The Philadelphia Pho
oqrapher says At brief intervals the question of tho
permanenee OF ordinary silver prints up again
and again for discussion. The loss, when the fading
takes place. almost always serious, often irreparabs
and those whom IL falls apt aud not unnafuraly
to express themselves with Indignation He repeats the
conviction often before expressed that a welLmadc
silver print albuminized paper. Ia perfectly perma-
nent II kept with ordinary care. print placed in an
album or portfolio laid between the leaves OF book
and left atmosphere not damper otherwise more
last indefinitely. II il does not the fault Is With the
maker of the print and not with the process Seven
years ago he printed silver positves by different
cut them 10 pieces aud oned these pieces
various ways which ne recoants and then subdvided
them and treated them with Various destructive agen
All of these specimens well the
for COMPARISON fastened notebook and tha
mode OF production aud aftertreafment carefully reys
tered. After an interval OF between seven and eight
years. the Orignsls-thaf To the portions Of ba
prints which not subjected 10 any Destructive
agency-are fitted 60 give useful information as to thai.
resisting powers ~ time Not "a single specimen pra
duced by any OF the ordinary methods OF printing AMI
toung faded. He therefore concludes tea, 1919,
prints made bv the methods after ia, s. "a
shorter interval give Indications of perishng rhcre
been grave want or care the part of fhs nr,rs
The fault lies ~ every photographer knows I'M fhs
poying OF hyposuph1e that has been preyiouslv nd
III nxins too miiy prints In given quantity Of hypsa
suphite and In insufficient badly MANAGED ..sh,p ~
The wrong that has been done 20 p6osograpl,v hv
cct OF tnese simple precautions has been iaeacu,as
Even at the present day feels any eerainS
pure nssed photograph will last more than vs.s sHas
anere snould DC some way OF reaching and pnn,.h
III tnoss VINO IMPOSE on the public with half ashsa