During the late dull weather, many of my plates have shown a tendency to an uniform leaden-looking deposit, destroying the blacks of the picture. A little more nitric acid in the bath will sometimes overcome this, but I have not yet found a sufficient remedy. During the summer months I was in the habit of using double the quantity of {187} iron I have stated, diluting the solution more; then was compelled to diminish the quantity to twelve grains, and now I use eight. I have tried the proportions recommended by French photographers, but they seem to contain too large a proportion of iron. I prefer the use of the protosulphate to the protonitrate of iron from its cheapness, and the ease with which it is made up. It will also keep for any length of time, rather improving than otherwise. I back with liquid jet from Suggitt, opposite the House of Correction, Mount Pleasant, Clerkenwell. It dries rapidly, and brightens the appearance. G. H. P. _Mr. Weld Taylor's Iodizing Process._--The process I sent to your columns last month, for iodizing paper, is applicable _only_ to the paper of Canson Frères; and I may further explain, that if the solution does not answer well, it may be washed over again with a solution of iodide of potassa only of the usual strength, and then set on a dish of slightly-acidulated water, to assist the separation and set free the potash. To make the matter clear to MR. SHADBOLT, I may observe, to one who is in the habit of iodizing paper, a considerable amount of the passage relating to cyanide of potassa could not be misunderstood; the nitrate of silver being added to the iodide of potassa, forms at once a precipitate which it is required to take up. The old double iodide says, add iodide of potassa till it does so, and it will do so; but the cyanide of potassa does it much better, and the cyanogen is lost as the paper dries, otherwise it would take no image at all. In the process I gave it merely requires an equivalent, "and cyanide of potassa is always of use in many of these processes." That equivalent is of course best arrived at by a solution, as, if the cyanide of potassa were added in the lump, it would be lost or be in excess.