374 
POPULAR SCIENCE EEVIETV. 
is a matter of very great importance. It would astonish those who have not 
devoted much attention to metallurgical pursuits, to learn how sensibly the 
most minute traces of foreign metals interfere with the value of copper, 
rendering it, in many instances, hard and brittle when softness and mallea- 
bility are recpiired. So delicate are the manipulations requisite for the 
detection and estimation of all the impurities, often amounting collectively to 
only a few hundredths of a grain in one hundred of copper, that many 
experienced analysts have disagreed materially in the results of their investi- 
gations. 
The importance of a knowledge of chemistry to those who have the 
management of smelting works is well illustrated in an anecdote related by 
Dr. Lyon Playfair to Dr. Percy : — “ At large chemical works, where sulphate 
of copper was prepared by dissolving copper in sulphuric acid, an insoluble 
residue was produced in the process, which had been put aside from time to 
time, and had not fortunately been thrown away. A small sum was offered 
by certain persons for this residue, which had not previously been regarded 
as of much value. Suspicion was excited, especially by the quarter from 
which the offer proceeded, and it was declined. The residue was examined 
and found to contain ,£700 worth of gold.” 
Dr. Percy does not seem to imagine that many improvements either in the 
economy of the prooess, or in the purification of the copper, have taken place 
during the last few years. Numerous patents have been registered, from 
time to time, for effecting not only a great saving in fuel, but also a better 
reduction of the metal, and yet nearly all the copper works have gone back 
upon the old system, the saving of time and fuel not appearing to compensate 
for the inferiority of the copper produced too rapidly. A smelter of great 
experience has assured Dr. Percy that better copper was formerly made by 
what was termed the dry roasting than that made at present by wet roasting. 
In the former case the regulus underwent a long course of treatment at a 
moderate heat, in which the volatile metals were eliminated ; in the latter 
the regulus is run down at once, and kept liquid until all the sulphur is 
expelled. 
It is to be regretted that our space will not admit of even a hasty glance 
at the metallurgy of zinc, which concludes the volume before us, a volume 
abounding in facts of the greatest importance, not only to the practical 
smelter but to the political economist and the philosopher. The statistical 
accounts of the quantity of coal annually consumed in metallurgic operations, 
the imports and exports of metals in their rough as well as their manufactured 
condition, the smelting of other countries compared with our own, cannot 
fail to interest all those who have the advancement and prosperity of these 
kingdoms at heart. The plates with which the work abounds are no ordinary 
illustrations, apt to mislead the novice in metallurgy, but true and correct 
sketches, according to exact scale, every line and altitude being accurately 
delineated. We must congratulate the scientific world upon the addition of 
a book to its library so full of useful information, and we must also congratu- 
late Dr. Percy upon the success which has attended his labours. 
