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POPULAR SCIENCE REVIEW. 
One of them is the concentration of copper, by burning the poor copper 
pyrites, in which process, after partial roasting, the outer rind of the ore 
is almost free from copper, whilst the centre of the lump contains a kernel 
composed of sulphur, which contains all the copper lost by the roasted 
envelope, often to the extent of 42 per cent. Another instance is that seen 
in the manufacture of white lead by the Dutch process. In the latter, 
during the formation of the several successive strata, it is found that ( a ) the 
impurities present themselves more abundantly in certain layers than in 
others ; and (b) also that the remaining uncorroded lead is far inferior in 
quality to that first employed. From this it has been concluded that the 
molecules have changed places during the process of manufacture. — See 
a Paper read by D. Zenner before the British Association at its late Meeting . 
Carbon as a Musical Sound-producer . — That bodies whose densities are 
similar vibrate similarly appears to be shown in some recent experiments 
of Dr. Phipson’s. He found that when a piece of homogeneous wood 
charcoal, about a foot long and an inch thick, is suspended by a string 
and struck with a hammer, it emits a beautiful musical sound, resembling 
that produced by glass under like circumstances. An experiment upon a 
bar of aluminium gave the same results. The densities of the three 
materials are : — 
Glass 2 # 49 
Amorphous carbon 2*50 
Aluminium 2*62 
The resonance of glass lasts, according to Dr. Phipson, for about five 
seconds ; that of aluminium about four seconds ; and that of charcoal from 
one and a half to two seconds. 
New Method of Measuring the Chemical Action of the Sun’s Rays. — This 
has been discovered and recorded by Dr. Phipson. The discovery appears 
to have been accidental, and to have resulted from the effect of light upon 
a solution of molybdic acid. A bottle containing the latter in an excess of 
sulphuric acid was exposed to the sun for about three hours every day, and 
became bluish-green during the daytime, and again colourless at night. 
The experiment was several times repeated with the same result. There 
was no evolution of gas. It appears that during daytime a certain amount 
of molybdic acid loses one atom of oxygen, which combines with the water, 
and during the night this binoxide of hydrogen gives back its borrowed 
atom. Now, a weak solution of permanganate of potash destroys the 
greenish colour produced by the action of the sun’s rays ; and hence 
nothing can be simpler than the estimation of the actinic power by the 
quantity of permanganate required to remove the colour. The variation 
of the actinism is represented by curves similar to those of the barometer, 
which may possibly be related to them. Dr. Phipson thinks he may be able 
to employ the oxalate of peroxide of iron to obtain more rapidly the same 
results as those achieved with molybdic acid. — . Vide a Paper read before 
the British Association at Newcastle-on-Tyne. 
The Absorption of Gases by Charcoal. — The following is a summary of 
the observations of Dr. Angus Smith, F.R.S.,upon this subject : — 1. Char- 
coal absorbs oxygen so as to separate it from common air, or from its 
mixtures with hydrogen and nitrogen. 2. It continues the absorption of 
