REVIEWS. 
373 
the results of some very interesting experiments of Matthiesson’s are given, 
showing that the concluctibility of metals depends not only upon their 
chemical purity, but also upon their molecular structure. Hence, the con- 
ducting power of pure silver wire, hard draum, is stated as equal to 100, but 
when annealed * it is 110 ; and copper, wdiich possesses the same power to a 
nearly equal degree, viz. 99'5, when hard drawn, only increases to 102 when 
annealed. The practical importance of these experiments must be apparent 
to every one, as upon the conductibility of metals, the whole system of the 
electric telegraph depends. 
A great portion of the work is devoted to the study of the various kinds of 
fuel used at different periods for metallurgic purposes, and in the article upon 
coal there is an interesting notice of the occurrence of certain metals in 
the fuel we ordinarily consume. Daubre'e has detected traces of antimony 
and arsenic in the coal of Newcastle-upon-Tyne, and in a variety of coal at 
Ville, in France, as much as 0’0415 percent, of arsenic, besides traces of anti- 
mony and copper. “I have seen,” continues Dr. Percy, “galena (sulphide of 
lead) in coal from Bedworth, and the anthracite of South Wales, which we 
have been accustomed constantly to employ in the metallurgic laboratory of 
the school of mines, contains decided traces of copper.” 
The subject of copper smelting is entered into minutely in all its important 
bearings, commercial, statistical, and scientific. Speaking about the enormous 
amoimt of poisonous gas annually exhaled from the copper-works of Swansea 
alone, Dr. Percy quotes Le Play as the author of the following interesting 
facts : — “ Sulphurous acid forms twenty-one per cent, of the total weight of the 
sum of the fixed and volatile products of calcination, and twenty-five per cent, 
of the weight of the ore subjected to calcination ; the weight of sulphur con- 
tained in this gas amounts to thirteen per cent, of that of the ore. During the 
entire process of smelting, the sulphurous acid and sulphur expelled amount, re- 
spectively, to fifty-six and twenty-three per cent, of the weight of the ore. The 
total weight of copper ore smelted in South Wales (some time before 1848) being 
about 200,000 tons, about 42,000 of sulphur were annually volatilized, pro- 
ducing 92,000 tons of sulphurous acid. In the works situated near Swansea, 
nearly two-thirds of the ore imported into South Wales are smelted, so that 
daily 65,900 cubic metres of sulphurous acid are projected from these works 
into the atmosphere. This acid, being very hurtful to vegetation, not a blade 
of grass will grow on the neighbouring hills, which are particularly exposed 
to its influence. The sulphuric acid contained in the copper smoke is probably 
more injurious than the sulphurous acid, as every drop of rain, in falling 
through the smoke, becomes a solution of oil of vitriol, which, alighting upon 
foliage, is rendered more corrosive by subsequent evaporation of a portion of 
the water. The value of the sulphur annually dissipated is estimated at 
£ 200 , 000 .” 
The elimination of the various metals usually found associated with copper 
* The process of annealing generally consists in allowing the metal to cool 
gradually, during which operation certain valuable properties are conferred 
upon it, depending, it is supposed, upon a different state of the physical 
arrangement of the atoms. When hard drawn, the annealing has been dis- 
pensed with. 
2 c 2 
