14 (J&ppen 
sary to employ this acid in the previous part of the ana- 
lysis, the metallic contents should either be first precipi- 
tated by an alkali and redissolved in muriatic acid, or the 
nitric solution should be evaporated to dryness, redissolv- 
ed in muriatic acid, and again dried and moderately heat- 
ed for some time, whereby the nitrous acid is expelled,, 
and a metallic muriat remains for further treatment. 
Instead of iron, tin or especially zinc may be used as 
the precipitant of the copper from its solution : these act 
more speedily and with equal certainty. With either of 
these two, as their muriat is colourless, the total absence 
of the copper (provided iron or nickel is not at the same 
time present) is seen by the solution becoming entirely 
void of colour. 
Mr. Chenevix has also remarked * a singular circum- 
stance in these precipitations, which is, that h the acid, 
(particularly the muriatic) be in excess, a quantity of" 
hydrogen is disengaged, as occurs in the common solu- 
tions of these metals, and the whole of the copper is se- 
parated in a very short time. With muriat of copper, 
zinc, and an excess of muriatic acid, the separation is sur- 
prisingly rapid, and much advantage may be made of this 
fact in the analysis of copper ores. 
It is to be observed, however, that zinc will precipitate 
iron as well as copper from its solutions, but scarcely any 
of the iron will separate till all the copper is precipitated. 
Thus if zinc is added to a mixed solution of sulphat or 
muriat of iron and copper, the first precipitate is obvi- 
ously copper and little else, but at the time w hen the solu- 
tion begins scarcely to turn blue with ammonia, a black 
powdery oxyd of iron mixes with the copper. Even if 
no iron be contained in the cupreous solution, if there is 
an excess of acid, and common zinc (which always con- 
tains iron) be used, some of it will still appear in the pre- 
cipitate ; the excess of acid appearing first to dissolve 
*Phih Trans, for 1801, p. 211. 
