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POPULAR SCIENCE REVIEW. 
vapour of benzol absorbs the chemical rays more powerfully than coal 
gas, but if the vapour of ether, chloroform, or oil of turpentine, was sub- 
stituted for that of benzol, the effect was much less marked. 
Of eighteen different liquids water was found to be the most freely 
diactinic, and though eminently transparent to the chemical rays, it is less 
so than atmospheric air and certain other gases. Absolute alcohol is 
next, but exhibits a considerable falling off. Then follow Dutch liquid, 
chloroform, ether, benzol, glycerine, fousel oil, wood spirit, oxalic ether, 
acetic acid, oil of turpentine, glycol, carbolic acid, liquid paraffin, and 
bisulphide of carbon ; whilst tercliloride of phosphorus and oxychloride 
of phosphorus, although perfectly limpid and colourless to light, absorb 
all the chemical rays. Saturated solutions of potash, soda, phosphoric 
acid, and arsenic acid, exert considerable absorbing power. 
Of solids, the most perfectly diactinic are rock-crystal, ice, and white 
fluor spar, though less so than atmospheric air and certain other gases. 
Rock-salt is nearly equally transparent. Then follow the sulphates of 
baryta, lime, and magnesia, and those of the alkalies. The carbonates, 
borates, phosphates, and arseniates, of the alkalies and alkaline earths, 
are also tolerably transparent. Although the sulphates are generally 
freely transparent, the sulphites are much less so, and the hyposulphites 
absorb about three-fourths of the length of the spectrum, leaving only 
the less refrangible portion. The chlorides and bromides of the alkalies 
and alkaline earths, and soluble fluorides, are freely diactinic, but the 
iodides are much less so. Amongst the salts of inorganic acids the nitrates 
are the most powerful in absorbing the chemical rays, a solution of either 
of them absorbs all the more refrangible rays and reduces the chemical 
spectrum to less than one-sixth of its ordinary length. The chlorates have 
a much less powerful absorbing action. Organic acids and their salts 
strongly absorb the more refrangible rays in the following order : citrates, 
acetates, tartrates, and oxalates, the latter being the strongest. The dif- 
ferent varieties of sugar are freely transparent. 
The second portion of Dr. Miller’s paper treats of the Electric Spectra 
of the Metals. All the ordinary, and many rare metals were employed, and 
in all the experiments the image of the spectrum was received and fixed 
upon a photographic surface. In many cases, metals which are allied in 
chemical properties exhibit a certain similarity in their spectra ; for in- 
stance, iron, cobalt, and nickel ; also bismuth, antimony, and arsenic. 
Volatile metals generally give the strongest lines. Some of the experi- 
ments were made with the metallic electrodes immersed in various gases, 
and it was observed that certain gases, such as hydrochloric acid, sulphu- 
rous acid, and nitrous oxide, greatly resisted the passage of the electric 
sparks. 
A valuable paper on the stratified appearance in Electrical Discharges, 
by J. P. Gassiot, F.R.S., has been printed in Number 53 of the Proceed- 
ings of the Royal Society. He describes numerous experiments with a 
battery consisting of 3,360 pairs of plates, acting upon various rarified 
gases, in glass tubes ; and especially examines “ the effects obtained by 
varying the resistance.” He states that the stratified discharge from a 
single disruption of the primary wire of an induction coil, is identical in 
