Art. LIX.—Absorption of Copper from its Ammoniacal Solution by Cellulose in presence of Caustic Potash.
[Read before the Wellington Philosophical Society, 25th November, 1871.]
When a weak ammoniacal solution of copper containing a little caustic potash is poured upon a filter of Swedish paper (cellulose) the liquid which passes through the paper is quite or nearly colourless, and the filter is found to have retained all, or nearly all, the copper of such solution.
The form in which the metal is retained appears to be that of a greenish blue hydrate, this being in weak chemical combination with the cellulose of the filter associated with a little ammonia.
A solution similar to the above, except that cobalt is substituted for copper, is unaffected by cellulose. A nickel solution could not well be applied, as the potash rapidly precipitates the metal unaided.
The presence of tartaric acid, sugar, or albuminous matters, does not interfere in any way with the absorption of copper instanced, nor are any of these substances adequate to supply the part of ammonia in the absorption stated.
In testing liquids, therefore, for diabetes, etc., we may, by the use of filter paper in the manner indicated, remove any ammonia that may happen to be present in such solutions, by which we are enabled to be certain that any blueness of colour they may possess after such treatment is not due to the presence of an ammoniacal compound of copper.