Read at the January Meeting of the Photographic Society of Scotland.

"I shall commence with the preparation of the albumen. I take eggs of medium age, and having selected as many as I think will be required to coat the plates to be prepared, I break them one by one on the edge of the vessel that is to contain the albumen, and then separate the white from the yolk. Having picked out all the insoluble parts, I add to the albumen 30 drops of a saturated solution of iodide of potassium, and half a wine glassful of water to each egg. The whole is then switched up into a large mass of froth, and set aside till it falls. I should mention that it is very essential that the albumen be thoroughly beaten up; the froth must be quite stiff and thick. More or less iodide of potassium may be added, according to the quantity of nitrate of silver to be subsequently used, and the degree of sensitiveness desired; but it is not advisable to increase the quantity of chemicals beyond a certain point, as it is liable to cause the albumen to crack off.

"I now take a clean glass plate, and having exposed it for a moment to steam. from hot water, I pour the albumen plentifully upon it. The effect of the steam is to make the albumen flow freely over the plate. As soon as it has run over every part, the albumen is poured off. It is unnecessary to preserve what is poured off, as, unlike collodion, it must never be used again in the preparation of plates, even though again beaten up. I now hook the plate by the two opposite corners to a piece of bent wire, to which is attached a piece of worsted thread, so that when I hold the thread the plate is in a horizontal position, with the prepared face downwards. Holding it in front of a clear fire, or better, above a close stove, a rotating motion is given to the plate by twisting the thread, exactly as in the common form of kitchen jack. The centrifugal force then produced, causes the albumen to spread equally over the whole plate, what is superfluous running off from the edges. By no other means can so even a coating be obtained, and photographers are greatly indebted to Mr. M'Craw, of Edinburgh, for the exceedingly ingenious and simple invention. The plate is made to revolve till slight cracks appear in the albumen at the edges of the plate. It must now be at once removed from the fire, for if at all over-heated, the nature of the albumen is altogether changed. The cracks soon spread of themselves over the whole plate, which shows that the coating has become equally firm. in this state the plate may be kept some time.

"I now proceed to sensitize the plate--First, I breathe very freely over the whole of it, for the purpose of in some degree re-softening the albumen, as it absorbs far more silver in that state than if very hard and dry. A bath is prepared with 120 grs. of nitrate of silver, and 10 drops of glacial acetic acid, to the ounce of water. I dip the plate in this bath by a single movement, and immediately remove it. It is now to be rinsed, say three times, in the same cold water. If too much washed it will lose sensitiveness, and if too little, the silver will crystallize on the surface of the plate. It is now ready for exposure in the camera."

To illustrate the operation of taking and developing a picture on a prepared plate, a copy of a bas-relief of "Night," by Thorwaldsen, was arranged so as to be lighted by a single common gas-burner of a larger size. The camera,. was provided with a double achromatic lens of Voightlander, and fifteen minutes' exposure ware sufficient to secure a good impression.

On removing the plate from the camera, a saturated solution of gallic acid was poured on it, which caused the picture to appear in about two or three minutes, of a beautiful clear red colour. A tittle of the silver bath was now added to give density to the picture. In the course of fifteen minutes it became perfectly vigorous and black in. the lights,. and clear and transparent in the shadows.

"About one half the time of exposure in the camera would have been sufficient, but the picture been allowed to develop slowly; or hard pyrogallic acid been used in the development. Had honey been mixed with the albumen, the action would have been far quicker and more magical: but though pyrogallic acid acts more quickly, it does not give so intense pictures as gallic acid; and I have never succeeded in getting large pictures free from blisters when honey was used."

The picture was now fixed by pouring over it a solution of hyposulphite of soda, 40 grs. to the oz. of water, and then washed thoroughly by pouring over it a stream of water as gently as possible, so as not to break the coating o1 albumen. When dry it was finished, and; needing no varnishing, was ready for printing.

"I may add, that nothing can be easier than to coat plates for taking views of ruins, as a defect in the spreading of the albumen some times makes a positive beauty in the picture, as defective skies can be all stopped with daubs of black paint. But it is a more difficult thing to coat large plates all over so evenly as to give a picture of sky and distance, united in harmony with the foreground. This can be done however, if the manipulation of the albumen is well managed, and then the picture is more satisfactory and truthful than when the same is attempted with collodion or paper. By either of the latter processes the sky is generally so dense that when printed it leaves the paper so clean and clear that the result is like a white washed wall, instead of having an appearance of distance and air. In such photographs there is generally no "bridal of the earth and sky," but rather a complete divorce. Of course albumen is too slow a process to give moving clouds, but it invariably gives the feeling of sky and air."

"Under favourable circumstances, with a double Voightlander lens, from three to four minutes' exposure in the camera would be sufficient: the well-known views of Edinburgh, from Nelson's monument, which were about twelve inches square, having been taken with a single achromatic lens, had an exposure of about twenty minutes. Prepared plates would keep good without any material diminution of sensitiveness for two days before taking a picture; on keeping them longer than that time a good result might still be obtained, but the exposure would have to be correspondingly lengthened. They might be quite well developed a week after the plate had been prepared and the picture taken."