We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
Photographic technique
THE SECONDARY IMAGE IN THE DEVELOPMENT OF PYROGATEGHINE, AND ITS UTILISATION
Prof. Rodolfo Namias
General observations.
It is well known that in the development of the layer of gelatine bromure of silver with organic developers th^ oxidation of the developer is produced by the brome which separates from the bromide silver. All the products of oxidation are coloured, though not all in an equal degree. The presence of sulphite of soda delays or even impedes the formation of the products of oxidation.
By using the developers in these alkaline solutions — deprived however of sulphite — the most favourable conditions are obtained for a product of oxidation equivalent to the quantity of reduced silver : and as the products
of the oxidation are retained by the gelatine, which they render more or less insoluble, simultaneously with the reduced silver a secondary image is formed, composed of a coloured material which with reference to certain developers may be considered as being of quinone.
But if it is desired to verify the action of the principal alkalis deprived of sulphite we find that pyrogall and hydroquinone are oxidated so rapidly under the influence of the atmosphere that they immediately colour the bath and even the gelatine, and that the bath quickly loses its developing qualites.
Other developers, such as paraphenylenediamine, oxidate and colour onlv
Editor's note. — This contribution from our eminent collaborator and friend, Professor Rudolph Namias, the founder and Director of the Institute of Chemistry and Photochemistry in Milan, an eminent technical expert, was recently presented to the International Congress of Photography and Cinematography at Dresden, where it was received with the greatest interest.
The question of which Mr. Namias treats is important not only for photography in the strict sense of the word but more particularly for educational and documentary cinematography .
Indeed the possibility of obtaining a better photograph and consequently the greatest effect from the lightest impressions is a notable achievement of the scientific documentary and didactic film. These various processes of obtaining pictures of superior opacity are of the greatest interest for the film from manifold points of view, especially for the sound film.
The results obtained by Mr. Namias after complicated sensometric and photomi co graphic experiments indicate the possibility of a great step forward on this path. The I.C.E., always ready to support all efforts towards technical perfection of the cinema, hopes that useful experiments may soon follozv in this field.