Photographic Reproduction Processes

he paper. To illustrate this curious and (so far as applications go) highly important property, I shall mention incidentally the results of some experiments made during the late fine weather on the habitudes of gold in presence of oxalic acid. It is well known to chemists that this acid, heated with solutions of gold, precipitates the metal in its metallic state; it is upon this property that Berzelius has founded his determination of the atomic weight of gold. Light, as well as heat, also operates this precipitation; but to render it effectual, several conditions are necessary:--First--the solution of gold should be neutral, or at most very slightly acid; secondly--the oxalic acid must be added in the form of a neutral oxalate; and thirdly--it must be present in a certain considerable quantity, which quantity must be greater the greater the amount of free acid present in the chloride. Under this condition, the gold is precipitated by light as a black powder if the liquid be in any bulk; and if