Improvements in and connected with the Removal of the Fixing Agent from Photographic Plates and the like.
Year: 1894

page_text: Date of Application, 16th Mar., 1894
Complete Specification Left, 14th Dec., 1894-Accepted, 19th Jan., 1895
PROVISIONAL SPECIFICATION.
Improvements in and connected with the Removal of the Fixing
Agent from Photographic Plates and the like.
1, AUGUST ZIMMERMANN, of 6 and 7 Cross Lane, St. Mary-at-Hill, in the City
of London, Merchant, (a communication to me from abroad by The Chemische
Fabrik auf Actien, vormals E. Schering, of 170/171 Mullerstrasse, Berlin, in the
Empire of Germany,) do hereby declare the nature of this invention to be as
follows:-
Complaints are constantly heard of incomplete elutriation of the sodium fixing
agent from silver pictures and consequent discolouration of the photographs.
Chloride of lime and eau de javelle, which have been repeatedly recommended for
destroying the last traces of the fixing agent (hyposulphite of sodium) and con-
sequently shortening the elutriation process, have only been attended with slight
success on account of their extremely inconstant composition; they have also other
drawbacks.
It has now been found that the salts of persulphuric acid are excellently adapted
for rendering an excess of hyposulphite harmless by oxidation. After the photo-
graph has been fixed the plate or paper is immersed in a dilute say a 1 per cent.
solution of persulphate of potassium or of persulphate of ammonium, which is
preferably made slightly alkaline. Whilst otherwise it is necessary to wash for
hours before the wash-water no longer gives a yellow precipitate with silver nitrate,
the employment of persulphate effects the removal of all hyposulphite of sodium
within a quarter of an hour, and subsequent decolorisation of the plate is avoided.
Dated this 16th day of March 1894.
AUG. ZIMMERMANN.
Improvements in and connected with the Removal of the Fixing
Agent from Photographic Plates and the like.
I, AUGUST ZIMMERMANN, of 6 and 7 Cross Lane, St. Mary-at-Hill, in the City
of London, Merchant, (a communication to me from abroad by The Chemische
Fabrik auf Actien, vormals E. Schering, of 170/171 Mullerstrasse, Berlin, in the
Empire of Germany,) do hereby declare the nature of this invention and in what
manner the same is to be performed to be particularly described and ascertained in
and by the following statement :-
Complaints are constantly heard of incomplete elutriation of the sodium fixing
agent from silver pictures and consequent discolouration of the photographs.
Chloride of lime and eau de javelle, which have been repeatedly recommended for
destroying the last traces of the fixing agent (byposulphite of sodium) and con-
sequently shortening the elutriation process, have only been attended with slight
success on account of their extremely inconstant composition; they have also other
drawbacks.
It has now been found that the salts of persulphuric acid H,S,O, are excellently
adapted for rendering an excess of byposulphite harmless by oxidation. After the

page_text: photograph has been fixed the plate or paper is immersed in a dilute, say a
1 per cent., solution of persulphate of potassium, of persulphate of ammonium, or of
persulphate of sodium, which is preferably made slightly alkaline. Whilst otherwise
it is necessary to wash for hours before the wash-water no longer gives a yellow
precipitate with silver nitrate, the employment of persulphate effects the removal of
all byposulphite of sodium within a quarter of an hour, and subsequent decolorisation
of the plate is avoided.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
.claim is :-
The application of persulphates in photography for removing the hyposulphite
salts substantially as described.
Dated thio 12th day of December 1801
AUG. ZIMMERMANN.