236 MANUFACTURE OF SULPHATE OF COPPER. 
the copper furnace to be melted. The following shows the re- 
sult of two operations on the commercial scale. 
First Operation. — 5 cwt. 2qrs. of copper scales, 685 lbs. of sul- 
phuric acid, sp. grav. 1700, and a sufficient quantity of water, 
produced 5 cwt. 2 qrs. 24 lbs. of crystallized sulphate of copper ; 
also 122 gallons of mother-liquor, sp. gr. 1180, and 160 gallons 
of ditto, sp. gr. 1100. A certain quantity of sulphate having been 
obtained from a given number of gallons of each of the mother-li- 
quors, the total produce of sulphate of copper was estimated at 
1240 lbs. 2 cwt. 1 qr. 8 lbs. of insoluble copper remaining. 
Second Operation. — Copper scales 7 cwt., sulphuric acid, sp. 
gr. 1700, 800 lbs., water, q. s., produced crystallized sulphate of 
copper, 7 cwt. 1 qr. 14 lbs.; 138 gallons of mother-liquor, sp. gr. 
1176, and 116 gallons, sp. gr. 1080, total crystallized sulphate of 
copper was estimated (in the same manner as in the first operation) 
at 1651 lbs s ; the quantity of insoluble copper residue being 2 cwt. 
3 qrs. 18 lbs. In these experiments, water was used instead of 
the mother-liquor of a previous operation, the object being to as- 
certain the exact amount of salt obtained from a certain quantity 
of copper scales. 
A not unfrequent custom in the manufacture of sulphate of cop- 
per is the addition of the " pickle," or " dipping-liquor" of the 
coppersmith and brazier, to the solution of copper in sulphuric 
acid above-mentioned, and in some cases the pickle or dipping-li- 
quor alone is employed to furnish crystals of this salt, the excess 
of acid being neutralized with oxide of copper. 
The pickling or dipping process consists in the immersion of 
copper, brass, and other metallic alloys in an acid solution, for the 
purpose of removing the film of oxide with which the metal has be- 
come covered, and which oxide must be removed in order to render 
the metallic surface sufficiently clean for the reception of varnish, 
lacquer, or other finishing, as well as also for the coating of the 
surface of one metal with another.* 
There could be no objection to the use of this pickle or dipping- 
liquor, if copper articles alone were immersed in the acid; but as 
* In the tin-plate works, large quantities of sulphate of iron are obtained 
by the evaporation of the pickle in which the iron plates are dipped for the 
purpose of cleansing them, previous to their immersion in the bath of melt- 
ed tin. 
