NATURAL PHILOSOPHY. 115 



detail all the pains I took to discover what would not do, and to find in what 

 proportions and in what order the right materials could be best applied, I will 

 briefly give the formula which I have adopted, and by which the specimens 

 alluded to were produced : First, take the white of eggs, and add 25 per 

 cent, of a saturated solution of common salt (to be well beat up and allowed 

 to subside); float the paper on the albumen for thirty seconds, and hang up 

 to dry. Secondly, make a saturated solution of bichromate of potass, to 

 Avhich has been added 25 per cent, of Beaufoy's acetic acid. Float the paper 

 on this solution for an instant, and when dry it is fit for use. This must be 

 done in the dark room. Thirdly, expose under a negative, in a pressure 

 frame, in the ordinary manner, until the picture is sufficiently printed in all 

 its details, but not over-printed, as is usual with the old process. This re- 

 quires not more than half the ordinary time. Fourthly, immerse the pictures 

 in a vessel of water in the darkened room, the undecomposed bichromate 

 and albumen then readily leaves the lights and half-tints of the picture. 

 Change the water frequently, until it comes from the prints pure and clear. 

 Fifthly, immerse the picture now in a saturated solution of protosulphate of 

 iron in cold water for five minutes, and again rinse well in water. Sixthly, 

 immerse the pictures again in a saturated solution of gallic acid in cold water, 

 and the color will immediately begin to change to a fine purple black. Allow 

 the pictures to remain in this until the deep shadows show no appearance of 

 the yellow bichromate; repeat the rinsing. Seventhly, immerse, finally, in 

 the following mixture : Pyrogallic acid, two grains ; water, one ounce ; Beau- 

 foy's acetic acid, one ounce; saturated solution of acetate of lead, two 

 drams. This mixture brightens up the pictures marvellously, restoring the 

 lights that may have been partially lost in the previous parts of the process, 

 deepening the shadows, and bringing out the detail; rinse, finally, in water, 

 and the pictures are complete, when dried and mounted. The advantages 

 of this process may be briefly stated as follows : First, as to its economy. 

 Bichromate of potass, at 2d. per ounce, is substituted for nitrate of silver at 

 5s. per ounce. Secondly, photographs in this way can be produced with 

 greater rapidity than by the old mode. Thirdly, the pictures being composed 

 of the same materials which form the constituent parts of writing-ink, it may 

 be fairly inferred that they will last as long as the paper upon which they are 

 printed." 



Gaudinet's mode of preserving Photographs on paper. I dissolve a certain 

 quantity of the gutta-percha of commerce in the Colas benzine. I decant in 

 a lew days, so as to have only the clear portion. I plunge my paper, sheet 

 by sheet, in this solution, and withdraw it almost immediately; then, hang- 

 ing it by a corner, I let it dry. I then present these sheets which contain the 

 gutta-percha as a powder, but not as a varnish, to a good fire. The grains of 

 gutta-percha unite, and cover the fibres, forming an interior varnish which 

 is nearly impermeable. 



I albuminize this paper which has lost none of its transparence (albumen, 

 100; rain-water, 25; chloride of sodium, G). I dry it, and render it sensitive 

 by a solution of 15 per cent, of nitrate of silver. I allow it to drip, and dry 

 it by a gentle fire; I produce a positive in the usual way, and fix it by 

 hyposulphite of soda at 10 or 15 per cent.; but this operation is so much 

 abridged, that in a few minutes the proof is fixed like one on glass, and of a 

 beautiful sepia tint. Nothing prevents the use of chloride of gold, if that is 

 The washing may be done in a quarter of an hour, in place of last- 

 ly 



