1st. He says, in answer to a previous Query, that "nitrate of potassa" is not formed in his process. Now I wish to ask if (as the iodide of silver is redissolved in iodide of potassium) it is not formed when the plate is plunged into the nitrate silver bath, as the nitrate decomposes the iodide of potassium?
2nd. How long will the collodion, according to his formulæ, keep, as collodion made with iodide of silver generally decomposes quickly.
3rdly. Why does he prohibit washed ether?
4thly. Does he think cyanide of potassium would do as well as the iodide, to redissolve the iodide of silver, iodide of potassium being at present so dear?
5thly. In his paper process, does not the soaking in water after iodizing merely take away a portion of iodides of silver and potassium from the paper; or, if not, what end is answered by it?
W. F. E.
Baths for the Collodion Process.—Having lately been assured, by a gentleman of scientific attainments, that the sensitiveness of the prepared collodion plate depends rather upon the strength of the nitrate of silver bath than on the collodion, I am desirous of asking how far the experience of your correspondents confirms this statement. My informant assured me, that if, instead of using a solution of thirty grains of nitrate of silver to the ounce of water for the bath, which is the proportion recommended by Messrs. Archer, Horne, Delamotte, Diamond, &c., a sixty grain solution be substituted, the formation of the image would be the work of the fraction of a second. This seems to me so important as to deserve being brought under the notice of photographers—especially at this busy season—without a moment's delay; and I therefore record the statement at once, as, from circumstances with which I need not encumber your pages, I shall not have an opportunity of trying any experiment upon the point for a week or two.
Upon referring to the authorities on the subject of the best solution for baths, I have been struck with their uniformity. One exception only has presented itself, which is in a valuable paper by Mr. Thomas in the 6th Number of the Journal of the Photographic Society. That gentleman directs the bath to be prepared in the following manner:
Into a 20 oz. stoppered bottle, put—