636 COPPER—IN NITRIC,—IN MURIATIC ACID.
mical change that we obferve is a nitrate of tin in the place of a nitrate
of copper, and the eruption of nitrous fumes. Some more oxygen
ſeems, therefore, to be necefsary for the new compound; and we ſhould
rather have looked for a diminution than an increase of heat ; unless
we admit the heat to be produced in the fame way as when alcohol
or sugar is added to nitric acid.
Paper, moistened with a solution of this nitrate, when held before
the fire, catches fire at a very low temperature,—not fufficient to melt
tin.
Theſe cryſtals are very fuſible, but it is a fort of watery fusion they
undergo ; for they are very retentive of water; and if we increase
the heat a little too high, the acid begins to evaporate, and carries
away a ſmall portion of the copper.
The muriatic acid diffolves this metal flowly. The colour of the
solution is at first dark brown, but becomes green by keeping. Sym
pathetic, or rather changeable ink, of Mr. Macquer, is prepared from
this solution.
The solution, when duly diluted, has a light blue colour, and when
spread on paper, exhibits the fame hue as long as any moisture ad
heres to it. But when flowly dried before the fire, and allowed to
attract the moisture again, it returns to its former state of an almost
imperceptible blue. In order to infure the disappearance when cold,
dip a pencil in the solution (very weak) of muriat of lime. Paſs this
over the copper solution,—it will not decompose it, but, by attracting
moiſture, will cauſe the colour to vaniſh almoſt entirely. Care must
be taken with this, and indeed with all thofe fympathetic inks, not to
let the paper become too hot. This scorches that part on which the
solution is spread, and makes it a permanent brown.
The scales of copper, formed by calcination, exhibit nearly the
fame appearances in solution in this acid. A recent and brown solu
tion of the scales, if largely diluted with water, deposits part of the
copper in the form of a white precipitate, super-saturated with cop¬