286 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Septembeb, 



PHOTOGRAPHY. 



Photngrapliy on Gehitine : — Mearui of obtaining very clear and very 

 Transparent Negative Proofi, capable of being transferred a great 

 many times on ordinary Photographic Paper. By M. A. Poitevi.n.* 



In order to prepare the layer of gelatine on which I make my 

 negative j)roof, I dissolve in luo grammes of water 6 grammes of 

 gelatine of good quality (that which is met with in commerce, and 

 which is used for preparing jellies for food succeeded best). This 

 size should not contain salts soluble in water; it should also be as 

 free as possible from fatty matters. To make the solution, I steep 

 the gelatine in distilled water for 10 or 1,3 minutes; I slowly heat 

 over a spirit lamp, and agitate continually until the solution is 

 cotiiplete. If any scum forms, I carefully remove it by means of 

 blotting paper, which I draw over the surface ; I strain it through 

 a very fine cloth, previously danijjed, and I again skim the surface 

 on which a few striae form, arising, doubtless, from fatty matters 

 which escape the first skimming. 



The gelatine being thus jirepared, I take, with a graduated 

 pipette, a determinate quantity, and I run it over a very even 

 plate of glass placed horizout;;lly ; a layer of l-SOmm. is sufficient; 

 this quantity is equivalent to nearly 'io centimetres of solution for 

 a surface of half a plate having 13'5c. or 17'5c. A thicker layer 

 would not be injurious, but a thinner one might present some in- 

 conveniences. 



Before running the gelatine on the glass plate, a thin layer is 

 applied to it by means of a cloth impregnated with a solution of 

 gelatine, rather more dilute than the foregoing; afterwards, the 

 glass plate is gently heated by means of a spirit lamp; then the 

 solution of gelatine is run on, and flows uniformly over the plate. 

 The under side of the glass plate is again heated, but with modera- 

 tion, in order to give fluidity to the gelatine, and is allowed to 

 cool. 



The plate being thus prepared, I plunge it into a solution of 

 acetate of silver, keeping the surface covered with gelatine under- 

 neath, and inclining it in the solution until the latter has com- 

 pletely moistened it ; I then turn the glass plate and immerse it 

 completely in the solution; then I pass a very soft pencil several 

 times, and in difi'erent directions, all over the gelatinised surface, 

 in order to dispel the bubbles of air which may adhere to it; and, 

 before withdrawing it, I blow on the surface to ascertain whether 

 the solution has moistened it all over. I then remove the plate, 

 and holding it somewhat inclined, I pass the pencil already used 

 over the whole surface, taking care to cover the edge of the pre- 

 vious stroke with that of the following one. I then dry the under 

 side of the plate, and i)lace it horizontally until the surface is dry, 

 which requires five or six hours. 



I ordinarily prepare over-night the plates which I intend to use 

 on the following morning, and in the morning those which I mean 

 to use in the evening. It is important that no free li(piid should 

 be left on the surface of the plate when it is required for use, for 

 the preparation would be removed at the places where any re- 

 mained. This preparation should be made out of the solar light. 

 The plate covered with the solution of acetate of silver should be 

 kept out of tlie light. 



The solution of acetate of silver is prepared by making a satu- 

 rateil solution of acetate of silver, to which half its bulk of water is 

 added. Admitting that 100 parts of water dissolve, at the ordinary 

 temperature, 0-S gr. of acetate of silver, to prepare 0-750 Jit. of the 

 solution which I use, I dissolve 2-5 gr. of acetate of soda in 15 

 grammes of water; I likewise dissolve 3-03gr. of nitrate of silver 

 in 10 grammes of water; I add the solution of nitrate of silver 

 to the solution of acetate of soda, and I receive the acetate of 

 silver which is precipated on a filter; I wash the precipitate in a 

 stream of water, then I pass through the filter several times 050 

 lit. of water; almost the whole of the acetate of silver should then 

 be dissolved; I afterwards add 0-25 lit. of water to the half litre 

 of saturated solution. 



In this operation 3 grammes of acetate of silver are formed, the 

 0*75 lit. should contain only 2-50 gr., but \ put in a little more of 

 it to make uj) for any that may have been lost in the water of the 

 solutions and of washing. The acetate of silver being very easily 

 altered by the solar light, I make this solution as far as possible in 

 a dimly-lighted place. I preserve it in a bottle covered with black 

 paper, and filter it every time I use it. 



1 e.xpose the plate prepared as above described to the vapour of 

 iodine, in the same manner as a plate of silvered copper; only, for 

 this exposure, account must be taken of the time, for we cannot 



• Comj)t« Jtauhu, Xo. 21, Maj 2", 1850.— Chciniit, July 1830. 



judge of the tint on the surface, only the time of exposure is 

 shorter than for silvered plates. The iodised plate is placed in 

 the frame of the camera obscura, and then I cover the side which 

 is not gelatinised with a piece of card-board covered with black 

 cloth. It is good to allow some time to elapse between the iodising 

 and the exposure to the focus of the camera; the plate thereby 

 gains in sensibility. 1 have sometimes used plates five or six hours 

 after the iodising; they had lost nothing of their sensitiveness. 



The sensitiveness of these plates is about one-fourth of that of 

 plates prepared with iodine and bromine. For a landscape with 

 much light and with an object-glass with a small diaphragm, the 

 exposure in the camera may require from 80 to 100 seconds. Por- 

 traits, with strong lights and shades, may be taken in two minutes 

 with the portrait object-glass. I have tried the effect of the 

 vapour of bromine on these plates, and have found that it renders 

 them more delicate. I have not made suflBcient experiments to 

 have certain data on this subject. 



In order to make the image appear, I plunge the plate into a 

 solution of gallic acid containing O'l gr. of gallic acid in 100 

 grammes of water; I leave the proof until the shadows appear 

 sufficiently intense. This immersion may last an hour or an hour 

 and a half. With a more concentrated solution of gallic acid, it 

 would require a shorter time, but it would be more difficult to 

 regulate its action. At the commencement of the immersion, a 

 positive image is formed on the surface of the gelatine. This 

 image becomes more and more dark; but, on looking through it, 

 the parts corresponding to the shadows in nature remain very 

 light. 



To fix the proof, it is washed in ordinary water, and then left 

 for about a quarter of an hour in a solution of 1 gramme of hypo- 

 sulphite of soda in 100 grammes of water; it is again washed in 

 ordinary water, and it is steeped for the same length of time in a 

 solution of 1 gramme of bromide of potassium, in 100 grammes of 

 water. 



I wash the proof with ordinary water, allowing it to remain in 

 it for fifteen or twenty minutes; then I wash with distilled water, 

 and allow the layer of gelatine to dry in the open air. It is then 

 a very clear negative proof, capable of giving positive proofs, with 

 ordinary photographic paper, in the sun, in from 2 to 10 minutes, 

 according to the vigour of the negative proof: it also comes very 

 well in the shade. 



It is well to renew, at each operation, the solutions of gallic acid, 

 hyposulphite of soda and bromide of potassium. 



In this operation, if the solution of gallic acid be replaced by a 

 solution of sulphate of protoxide of iron, very beautiful positive 

 proofs are obtained. 



Photography on Paper. — Means of obtaining the Imagein the Camera 

 Obscura on Dry Paper. I3y M. Blanqcabt-Evbard. 



To render the execution of photography on paper simple, sure, 

 and easy to those least experienced in chemical manipulations, 

 should be the object of the efforts of those who wish to bring this 

 art to its most useful application in industrial economy. The first 

 condition for entering into this new order of things, is to rid the 

 operation of the care which it requires at the time of the exposure. 

 Me o])en the way by giving here: — 



1. The means of operating on dry paper, instead of damp paper, 

 freeing the operator from the difficult preparations which he has to 

 make at the places of exposure. 



■2. So simple a mode of preparing this photogenic paper, that it 

 may be manufactured and sold to the amateur who does not desire 

 the trouble of preparing it himself. 



The papers prepared by the means hitherto described could not be 

 brought to the dry state without afterwards taking, under the 

 action of gallic acid, an uniform coloration which would efi'ace the 

 photogenic image, and cause it to completely disappear. Serum 

 has the property of obviating this inconvenience ; the following is 

 the mode of preparation to be adopted: — 



Collect, by filtering, the clear part of milk which has been turned, 

 and beat u|) in tliis serum the white of one egg to each pint, then 

 boil in order to remove all the solid matters, and filter again, after 

 which dissolve without heat 5 per cent, by weight of iodide of 

 potassium. The paper to be prepared must be very thick and 

 steeped entirely in the liquid for two minutes, and afterwards dried 

 by hanging it, by means of two pins, by two of its corners, to a 

 line. 



This preparation is made in the daylight without any particular 

 precaution ; the paper is fit for immediate use for six months after' 

 uud certainly after a much longer time. AVhen it has to be used 



