Photography

In 1923, motion picture film 16 mm. wide on cellulose acetate base was introduced packed in such a manner that it could be loaded into small motion picture cameras without the use of a darkroom. This film was designed for finishing by a reversal pro cess, in which the first negative is removed by a bleaching bath, and a positive is then printed on the remaining silver bromide. In 1932 a similar film 8mm. wide was introduced. The use of these films has led to a great advance in amateur cinematography.

Developing Agents.

In the Calotype process gallic acid was used as the developer for the latent image, but in 1851 Regnault of Paris and Justus Liebig simultaneously discovered the more energetically-acting pyrogallol, which actually allowed shorter ex posures to be given. This was used also at first for wet collodion, though it was later replaced by an iron salt, and for dry collodion plates. Until 1861, free silver nitrate was an important ingredient of developers; but in that year Wardley proved that pyrogallol alone could be used. C. Russell and J. Leahy independently announced alkaline pyrogallol development, the former suggest ing also an alkaline bromide as restrainer. Even after the intro duction of the gelatine plate, pyro-ammonia was the only de veloper used until 1884, when the alkaline carbonates became general. In 188o Abney discovered the developing properties of hydroquinone. C. Egli and Arnold Spiller recommended the use of hydroxylamine in 1884. In 1888, M. Andresen of Berlin patented the use of paraphenylene diamine, paratoluidine diamine, and xylidene diamine as developers. In 1891, he patented the use of paraminophenol and its derivatives, especially monomethyl paraminophenol, known under the trade name of "metol." Printing Processes.—In turning to the positive processes, the first was with silver chloride and excess of silver nitrate on plain paper, which gave prints with a rather sunken appearance, the image being more or less buried in the fibres of the paper, and daylight was essential for printing. Blanquart-Evrard, in 1847, suggested the use of albumen to keep the sensitive salt more on the surface. In the same year, Romieu proposed salting with a mixture of alkaline bromides and chlorides containing gelatine and subsequent floating on silver nitrate solution. A few years later,

the first coat of albumen was coagulated and a second applied, which gave a more brilliant glossy surface. The colour of prints obtained on these papers was an unpleasant foxy colour, and to darken this an acid was added to the fixing bath, thus causing sulphur toning. Le Gray, in 185o, proposed the use of a gold salt to improve the colour, and an alkaline gold bath was recom mended by Waterhouse in 1858. De Caranza, 1856, recommended the use of platinum in lieu of gold. Albumenized paper made in this way and toned with gold remained the standard photographic printing medium until 189o.

A. Gaudin had suggested an emulsion of silver chloride in collo dion for printing-out. This was revived by Wharton Simpson, in 1865. Paper thus prepared was introduced commercially by Ober netter three years later. Humbert de Molard, 1855, proposed to precipitate silver chloride, wash and suspend it in solution of starch or gelatine and paint the mixture on to paper. The same process was revived by Smith and Palmer in 1865 and by Abney in 1882. From this date, gelatino-chloride or printing-out paper came into general use, and eventually completely displaced al bumen. Printing-out papers are at present used in Europe, chiefly collodion papers containing a gold salt that obviates the necessity of toning, but in America their use is limited to the production of rough proofs. Commercially they have been superseded by devel opment papers.

Silver bromide with excess silver nitrate was used by Fox Talbot, and J. W. Swan in 1879 patented the use of paper coated with silver bromide emulsion not containing excess silver for development. It did not, however, come into general use until marketed by Eastman and by Just in 1883. Eder and Pizzighelli published, 1881, an exhaustive paper on gelatinochloride of silver with development, and the former, two years later, described a chloro-bromide emulsion. Chloride developing paper was intro duced by Marion in England under the name of "Alpha" in 1889, and by Baekeland in America as Velox. Year by year since then the use of this paper has increased, special types, including a great variety of surfaces, being used for amateur and professional work.