_Gallo-nitrate of Silver._--Can you inform me what the true nature of the
decomposition is which takes place after a short time in the gallo-nitrate
solution of silver? and if there be any ready means of rendering the silver
it contains again available for photographic use?
SIR W. NEWTON, in the description of his calotype process, says: "Bring out
with the saturated solution of gallic acid, and when the subject begins to
appear, add the aceto-nitrate of silver solution." Which way of doing this
is the best,--mixing the two solutions together and applying them to the
paper; or applying the paper, when wetted with the gallic acid, to the
silver solution?