M. TECHNOLOGY. 517 



then to pass over the written parts with a pencil moistened 

 in a weak solution of sulphide of ammonium, which in the 

 majority of cases will at once restore the legibility of the 

 text. The success of the process depends upon the fact 

 that the great majority of such old writings will be found 

 to have been made with an iron ink, and the action of the 

 sulphide consists in the production of a sulphide of iron with 

 the traces of iron yet remaining thereon. 



AN OIL -LAMP AS A SUBSTITUTE FOR THE MAGNESIUM LAMP 



IN PHOTOGRAPHY. 



Van Tenac exhibited, in Paris, an oil-lamp with a burner 

 so constructed as to admit a jet of oxygen directly into the 

 interior of the flame. The light produced was perfectly 

 steady, and so intense that the gas-flame appeared yellow 

 bv contrast. Although less actinic than the lisrht of the 

 magnesium lamp, it is suggested that, by reason of its uni- 

 formity, cheapness, and convenience of use, it may be em- 

 ployed by photographers for reproductions which need not 

 be produced rapidly. 15 (7, VI., 1875, 96. 



COMPOSITION FOR NON-ACTINIC (AMBER-YELLOW) GLASS. 



A yellow glass, suitable for photographic dark-rooms, that 

 is said to be more beautiful, purer, and more brilliant in color 

 than that colored with metallic oxides, can be made by em- 

 ploying dried cow's-dung as the coloring matter, in the pro- 

 portion of one part by weight of the dried and sifted dung 

 to sixty parts of the usual mixture for colorless glass. 13 

 (7, March ] , 1875, 318. 



ADVANCES IN PHOTOGRAPHY. 



In a review of recent discoveries in photography, Meldola 

 states that since the year 1842, when Becquerel photographed 

 the whole solar spectrum, and Dr. Draper the violet, blue, and 

 ultra red, no successful attempts have been made to photo- 

 graph the red end of the spectrum. Becquerel's result was 

 obtained by a film of silver iodide first exposed to diffused 

 light, and then to the action of the spectrum, by which proc- 

 esses he was able to photograph the entire spectrum from 

 the ultra violet to the ultra red. During the past year Dr. 

 Vogel has demonstrated that, by varnishing the ordinary 



