latent image may be very quickly developed. The papers however will not keep after being iodized.' "Mr. Muller suggests, that as iodide of lead is completely soluble in nitrate of silver, it might furnish a valuable photographic fluid, which could be applied at any moment when required. "No small degree of interest attaches to this process, originating in experiments carried on in Central India. It appears perfectly applicable to the albumenized glass and collodion processes." _Detail on Negative Paper._--I have not observed before this, that any photographic operator has "noted" the burnishing of the iodised paper previous to adding the exciting solution, though I know it is usual to burnish before taking a proof. This is a very useful adjunct to obtaining minuteness, and it is a plan I have sometimes adopted. I at first thought it would injure or knock off the iodized surface, but no injury whatever arises from the rubbing. I use a small piece of glass rod, polished flat at one end, so that it may present {204} a facet about half an inch square; but I should imagine a better instrument might be manufactured with a proper handle, and some mode of obtaining pressure; not obtaining sufficient is the cause of a little after-disarrangement if the nitrate of silver is laid on with a brush, but if floated the polish remains. It cannot be doubted but paper is adequate to any detail; and when a paper shall be manufactured of a perfect kind, there is no reason to suppose but paper generally will rival collodion for most purposes. Nothing prevents it at present but the uneven surface of paper. It is very nearly perfect in the French negative paper; but that has so many other drawbacks to its use that it cannot be safely depended upon. Our manufacturers have still some improvements to make; for if Canson Frères had left out the blackening chemical in the paper, it would have been better than any of ours in my estimation. WELD TAYLOR. _Ammonio-nitrate of Silver._--Will any of your scientific correspondents explain the chemical cause of my inability to form the ammonio-nitrate of silver from a solution of nitrate of silver upon which albumenized paper has been previously floated? Having excited some albumenized paper on a forty-grain solution of nitrate of silver, I kept the solution which had not been consumed for the purpose of converting it into the ammonio-nitrate. But on dropping in the ammonia, not only did no precipitate take place, but the ammoniacal smell which usually gives place to the tarry odour remained. No albumen appeared to be dissolved from the paper, and the solution had lost none of its silver, which I subsequently collected by means of having formed a chloride. This has occurred to me more than once, and I call attention to it, as the investigation of it may lead to some new results. PHILO-PHO. * * * * * Replies to Minor Queries.