M. TECHNOLOGY. 483 



monia from ferric chloride, and diluting it to 500 cubic cen- 

 timeters. Exposure to the sunlight under a drawing for a 

 quarter of an hour will afford an impression, which may be 

 fixed by washing it in water. 14 C, CCXVIII., 62. 



FRENCH METHOD IN ENGRAVING ON WOOD. 



A French method, in en2:ravino' on wood consists in first 

 covering the block with a layer of gelatin (0.39 gramme to 

 31 grammes of water) by means of a soft brush. When this 

 coating is dry it is covered, in the dark, with a solution pre- 

 pared of (1) red prussiate of potash, 7.80 grammes ; water, 

 62.20 grammes; (2) ammonio-citrate of iron, 9.10 grammes 

 in 62.20 grammes of water. These solutions are mixed and fil- 

 tered, and the mixture is kept in the dark. After the layer is 

 dry it is exposed under a negative from ten to twelve min- 

 utes, and washed with a soft sponge, when a blue image ap- 

 pears. If thus prepared the coating does not shell off" under 

 the graver. 5 yl, 1875, 98. 



RETOUCHING VARNISH FOR NEGATIVES. 



It is claimed that a film of the following varnish on nega- 

 tives, as suggested by Monckhoven, can be retouched with a 

 brush or lead-pencil three or four times as rapidly as one of 

 gum : Add common shellac, in scales, to a saturated aqueous 

 solution of carbonate of ammonia. After twenty-four hours 

 pour off the clear liquid, add about an equal quantity of wa- 

 ter, and bring the mixture slowly to boiling, while continu- 

 ally stirring it with a glass rod. A brown shellac solution 

 is thus obtained, and there should be about one hundred 

 parts of water to eight of shellac, and no odor of ammonia. 

 The negative, after being washed, should be flowed with dis- 

 tilled water and allowed to drain, and should then be coated 

 by flowing the varnish over it twice in succession. After 

 drying, the coating is brilliant and hard, and insoluble in 

 water. If many prints are desired, the retouched negative 

 should be varnished as usual. 18 (7, VI., 461. 



PHOTOGRAPHIC POWER OF ARTIFICIAL LIGHT. 



Comparative tests of the photographic effect of light from 

 different artificial sources have been made by Riche and Bar- 

 dy. Plates were sensitized with bromide of silver, and ex- 



