From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 05/24/01-02:40:27 AM Z
At 11:33 PM 05/23/2001 -0400, you wrote:
>
>Perhaps this belongs on the Photo History list - but since the subject
>is gelatine, cows and mustard from days gone by I thought I'd pass
>this along (some of my notes on THE AMERICAN ANNUAL OF PHOTOGRAPHY:
>1926):
>
>Neblette, C.B. "Photographic Review for 1925: Emulsions. THE AMERICAN
>ANNUAL OF PHOTOGRAPHY: 1926. Vol XL. Ed Percy Y. Howe. New York: The
>American Annual of Photography, Inc. c1925., pgs 22-28.
>
>Lamenting the lack of information available about emulsion manufacture
>(from the manufacturers) and after noting "a growing tendency,
>particularly on the part of the larger manufacturers, to the
>circulation of reports of investigations on the basic problems of
>emulsions, and not with the actual details of emulsion manufacture,"
>Neblette remarks on a paper published by Dr. S. E. Sheppard dealing
>with "the separation of gelatine-X." Neblette states, "presence of
>which [Gelatine-X] in ordinary gelatine is chiefly responsible for
>photographic sensitiveness;" and "This substance... was found to be
>closely identified with allyl-mustard oil or allyl
>sulphide... discovered to be allylisothiocyanate." Neblette adds,
>"this [Gelatine-X ??] is present in ordinary gelatines in extremely
>small quantities, not more than one part in a million and reacts with
>the ammonia used in the digestion of the emulsion and with amines to
>produce allylthiocarbamide, which is the active in producing
>photographic sensitiveness." Neblette then goes on to sight numerous
>papers concerned with the subject of emulsion sensitivity.
>
This story has been told often but the first really complete version I've
seen is in
Elizebeth Brayer's recent biography of George Eastman (1). Its at the
beginning of chapter three. The emulsion failure happened in 1882. Eastman,
after extensive investigation of his emulsion making processes traveled to
England with his partner Henry Strong, and his emulsion assistant Walter
Butler. What they found is that Eastman's source for gelatin had changed
their supplier of the raw materials, i.e. hides and bones. When gelatin
from the original source was used the emulsion returned to its former
quality. They had no idea at the time of why there was a difference but
assumed it was due to some impurity in the new gelatin. The probable reason
was not discovered until some forty years later at Kodak Labs by
S.E.Shepard, Mees's old school chum and friend. Shepard discovered the
importance of traces of sulfur compounds in increasing the sensitivity of
the halides. They speculated that the reason for the original emulsion
failure was not due to impurities in the gelatin but, rather, the lack of
them. The source of the story about the cows eating mustard stems from a
book 1937 book by C.E.K.Mees where he makes this claim. I have the second,
revised edition but can't find the story of the failed emulsion in it.
However, Mees does discuss Shepard's discovery of the sensitizing abilities
of sulfur compounds and mentions one source as being the diet of the
amimals from which the gelatin is derived (2). I think I have the first
edition of this tome somewhere but have no idea of its location right now
(I think my books move around by themselves when I am not at home).
A couple of afterthoughts. The word Gelatin does not appear in the index
of Ms.Brayer's book.
Its very much worth reading.
Neblettes' books need to be read with some care. He got too much of his
data second hand and sometimes didn't get it quite right. There are minor
errors which persist through editions. A small example is the name of a
Gundlach-Manhattan lens called the RADAR he has it RADIAR in every edition
and in his little lens book.
1, _George Eastman a Biography_, Elizabeth Brayer, 1996, Baltimore: The
Johns Hopkins University Press ISBN 0-8018-5263-3
2, _Photography_ Second edition, revised, C.E.K.Mees, 1942, New York: The
Macmillan Company
---- Richard Knoppow Los Angeles,Ca. dickburk@ix.netcom.com
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