Color photography and printing

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  • 428 CURRENT TorIcs.

    The French Photographic Society announces its fourth com- petition in color photography, which is open to all photographers, amateur and professional. All classes of work may be submitted, including subjects for window transparencies, lantern slides and stereoscopes. Prints should he accompanied by a description of the subject they represent and the conditions under which they were taken. Numerous medals will be awarded by the jury. .The entries close on April 15th next.

    Color Photography and Printing. G. BANGS A. DUMEZ, and A. DE SEAUVE. (En,n. Pat. 20,251, Sept. 12, I~II.)-A set of three color filters is prepared by the use of the folllowing solutions (the quantities are those required for one square metre) : Red, 64 C.C. of I per cent. erythrosin solution, or IO C.C. of I per cent. Bengal Pink s$ution; ~lellozer, 115 C.C. of I per cent. Tartrazine solution; blue, 5 C.C. of I per cent Carmine Blue and I C.C. of I per cent. Naphthol Green solution. Each filter is also impregnated with about IO grammes of potassium nitrate per square metre. In con- junction with these filters positive films are employed which can be sensitized with bichromate, the red film consisting of gelatin stained with madder lake and spread on paper to the extent of 8.5 grammes per square metre; the yellow film is impregnated with cadmium sulphide, spread to the extent of 12.8 grammes per square metre, and the blue film is obtained by precipitating a solution of a ferric salt( e.g., by ferrocyanide) and mixing the precipitate with gelatin, using about 6 grammes per square metre. A series of scales of primary colors and of gray, which are photographed at the same time as the subject of the pictures, is also used to check exposures and development of the photographs. The positive films are pre- pared on paper which has been parchmentized by sulphuric and nitric acid and subsequently dipped in a solution of gum-lac in alcohol.

    Variations in Temperature Coefficients cf a Precision Bal- ance. J. J. M.\SLET. (Roy. Snc. Proc., Sm. A, lxxxvi, 591.)-In a previous paper the apparent abnormal behavior of certain precision balances was described and discussed. One point dealt with the displacement of the resting-point of a beam, dependent upon a uniform rise or fall in the temperature of the instrument. The amomunt of such displacement for a change of I C. was termed the temperature co,efficient o,f a balanlce. In this paper attention is directed to changes which may occur in the temperature coefficients of delicate balances. Peculiarities noted with a new balance dis- appeared after colntinued careful use of the balance. The conclusion is drawn that before a new, or comparatively new, precision bal- a&e can be safely used for obtaining trustworthy values of the highest order of accuracy the instrument must be suitably aged. A method of effecting this is suggested.