If the picture will not develop, from too short exposure in the camera, a solution of pyrogallic acid, as Dr. Diamond recommends, after the gallic acid has done its utmost, greatly increases the strength of the blacks: it slightly reddens the whites, but not in the same ratio that it deepens the blacks.
After the first wash with gallo-nitrate, it is essential to develop these strongly iodized papers with gallic acid only: the half-and-half mixture of aceto-nitrate and gallic acid, which works well with weaker papers, turns these red.
The paper I use is Whatman's 1849. Turner's paper, Chafford Mills, if two or three years old, answers equally well.
M. L. Mansell, A.B. M.D.
Guernsey, Jan. 30, 1854.
Footnote 4:[(return)]
[Having lately prepared this solution according to the formula given by Dr. Diamond (Vol. viii., p. 597.), in which it required 650 grains to dissolve the 60-grain precipitate, we were inclined to think our correspondent had formed a wrong calculation, as the difference appeared so little for a solution more than one-third stronger. We found upon accurately following Dr. Mansell's instructions, that it required 734 grains of iodide of potassium to effect a solution, whilst we have at the same time dissolved the quantity recommended by Dr. Diamond with 598 grains. This little experiment is a useful lesson to our correspondents, exhibiting as it does the constantly varying strength of supposed pure chemicals.—Ed. "N. & Q.">[
Replies to Minor Queries.
Ned o' the Todding (Vol. ix., p. 36.).—In answer to the inquiry of W. T., I beg to say that he will find the thrilling narrative of poor Ned of the Toddin in Southey's Espriella's Letters from England, vol. ii. p. 42.; but I am not aware of any lines with the above heading, by which I presume W. T. to be in search of some poetical rendering of the tale.