The San Francisco call., 1910-07-14
CHEMIST TELLS
OF new METHODS
INPHOTOGRAPHY
President Bancroft Thinks Pos
tive Exposures Will Be of
Commercial Use
II. E. Barnard Discusses Effects
of Sodium BenzOate as
a Preservative
Subjects of Interest Discussed
by Experts in Various Lines
of Research

Rested from the trials of Mondays
Journey TO San Francisco more than
200 members Of the American chemical
society gathered in the colonial ball
reom Of the St Francis hotel early
yesterday morning for the opening ses-
sion OF the forty-second annual con-
ventfon. The meeting was called to
order. and Arthur Lachman, in behalf
Of the California branch of the organi-
cation, made a brief address Of well
come. 10 which President W. D. Ban
croft responded.
In his talk Bancroft indicated Cali
fornia as the worlds greatest field for
development in scientific and other
lines and predicted for San Francisco
= remarkable future. painting it as the
ultimate empress of the earth, with
other great cities as tributaries"
Bancroft opened the mornings dis
cussions with an illustrated address on
positive photography. in the introduc-
ton Of which he stated that the sub
sect, although OF no practical value as
pet was Of considerable interest In
the beginning he sketched briefly the
GEkGlODnenL along pIQl0E lJAiAN -A4ACS
and told Of how the first theories in
connection with positive photography
were evolved from exposures taken OF
the sun. Positive photography he eX-
plained simply as the taking Of the
picture direct on the Photographic
plate instead Of taking the usual neg
ative" or reverse from which ordinary
pictures are printed as positives- He
said that several snaps were taken Of
the sun with an ordinary camera. the
time OF the exposures being length
ened at each trial When the first
plate was developed it showed the
usual negative, that is, the sun ap-
peared as q dark spot on a light back
ground As the time Of the exposure
was heightened the plate when devel-
oped showed signs Of becoming posi-
tive and after several trials an actual
positive plate was made, the sun ap-
pearing d white spot For the sake OF
experiment moro exposure We're taken
but as the time was heightened be-
yond that when the plate was found TO
be positive IL was found that the tend
encv was toward the negative again.
This alienation between positive and
negative. according 70 the length Of
exposures, led 10 a great deal Of theor-
lzinE.
Bancroft showed many interesting
lantern slides Of the different phases of
positive photography. He dealt with
the so called "black lightning" and
demonstrated how the phOtographing of
lightning could be made black or white
at viii.
NEW PHOTOGRAPH
He closed with the statement that 1t
was his belief that positive photography
would eventually lead to the ability OF
the every day photographer to take
snapshots indoors or in subdued light
at VIII without the use of flash powder.
Professor Edward c. Franklin lee
tured on liquid ammonia as a solvent
After Franklin w i. Hillebrand read
a paper on Chemistry in the Bureau of
Standards" H z. Barnard closed the
morning session with a discourse upon
the use Of sodium benzoate as a pre-
servative Of food.
Barnard dealt with preservatives in
general before speaking of the benzo-
ate. He said that one Of the first in
dications Of civilization was the primi-
tive methods used in smoking and salt
ing meat for keeping. The necessity.
he said. continued to grow with the de-
velopment OF the race until in the pres
ent day Ii is a vital part of economic
life. Bernard said that there was a
great deal to be said in favor Of the use
Of benzoate; that it opened the way
1or the use Of poor raw materiaisN on
the part Of the manufacturer. OF the
cases where the chemical has proved
evil. he said. 1t had been put up with
fruit and vegeta bles of acid character
and formed q dangerous chemical COM
bination with it,
Yesterday afternoon the chemists
made an excursion on the Ocean Shore
line and in the evening were enter
n tned by a smoker and supper at the
A'airmont hotel The women of the
party were taken TO the Columbia the
ster.
Following is the program for today:
70 Division meetings at the ST. Francis ho-
tel. $50 q m; Industrial chemists and
p. chemical engineers, in assembly room,
the meeting 70 take the form of a SYM
postum on the subject Of smelter smoke.
Papers viii be presented by Charles
Baskerville, ". c. Ebaugh and F. c.
Cottrell.