Whip these up, till they are converted entirely into a white froth; when this has settled into liquid, pour it into a tall jar, and allow the precipitate, which will then separate, to settle completely, and strain the supernatant liquid through fine muslin. The paper, being laid on the surface of this fluid for a space of from five to ten minutes, may be taken off and hung up by a crooked pin to dry, and then ironed. It is to be sensitized with nitrate of silver, 120 grains to the ounce of water. The setting liquid I use is prepared according to the formula given by me in Vol. vii., p. 534. of your journal, except that I prefer to use half to one grain of pyrogallic acid, and 120 grains of chloride of silver. This paper must be soaked for a few minutes or so in rain water, after being printed, before being placed in the hypo.; the presence in the water of any salt seems to destroy the tone of this paper. Florian, Torquay. _Muller's Processes--Sisson's Developing Solution._--I am glad to find that I have called the attention of your photographic correspondents to Mr. Muller's process, as detailed in _The Athenæum_ of Nov. 22, 1851, which seems to have been strangely overlooked and neglected. As your correspondents have induced you to reprint the article, perhaps you will also yield to my request, and reprint an article from the same journal of later date (Jan. 10, 1852) containing another process, more economical and more sensitive than the other, invented also by Mr. Muller, and the value of which I have proved. In that, as in the other, there is no developing agent required. To save time I have copied from my note-book the article itself, and append it to this communication. A photographer of several years' standing informs me that my developing solution produces excellent negatives upon glass, and that he has been trying it as a bath with success. He writes me:--"I use your developing solution for negatives only; and by using a very small opening, say about 3/10ths of an inch diameter, single achromatic lens, I have produced negatives in one minute, which print most beautiful bright positives. The views I have taken and developed with your solution were without sunshine, the sky very cloudy, three o'clock p.m. The collodion was prepared by Messrs. Knight & Son." Since I received his letter I have tried a negative so developed, with the best success; and I attribute the success to the fact that you may go on developing with that solution any length of time almost, without any fear of spoiling the negative, thus getting thickness of deposit; and that the deposit on pictures taking so long a time to develop has a very perceptible yellow tinge, which, like the gold in Professor Maconochie's method (detailed in _Photographic Journal_ for this month), stops the chemical rays. J. LAWSON SISSON. Edingthorpe Rectory. "Patna, India, Nov. 9, 1851.