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POPULAR SCIENCE REVIEW. 
sion under the influence of heat, and its contraction when acted on by 
electricity, are all readily explicable on this hypothesis. As there are no 
facts to prove that the number of its atoms is three rather than four or five, 
its density must be known before any certain conclusion can be drawn on 
this point. 
Characters of Rain- Water. — M. Robinet finds that his experiments, 
conducted through a period of eighteen months — from March, 1862, to 
September, 1863, — enable him to draw the following conclusions: — (1.) 
Disturbance of the atmosphere does not seem to influence the quantity of 
fixed matter dissolved in rain-water. (2.) The proportion of fixed matter 
is not influenced by day or night. (3.) Frequently, after prolonged 
droughts, there is found a large quantity of fixed matter, but this is not 
constant. (4.) If successive portions of water from the same shower, or even 
the water of successive showers, be examined, it will be found that there is 
less fixed matter in the later than in the earlier collected portions. (5.) Paris 
rain-water contains chiefly sulphate of lime and an imperfectly known 
form of organic matter ; the proportion of sulphate of lime being about 
20 grammes to the cubic metre. (6.) Rain-water is more liable to froth 
when shaken than any other form known. ( 7 .) When nitrate of silver is 
mixed with Paris rain-water it is found to produce a reddish colour of 
various hues, and a deposit of a garnet-tint which contains the silver. 
(8.) The nature of the substance which produces this phenomenon is 
unknown. — Comptes Rendus , lvii. No. 10. 
Chemical Composition of Corn found in Pompeii. — The corn which was 
discovered among the ruins of the buried city has been analysed by M. S. 
de Luca, who has presented his second memoir to the French Academy. 
After eighteen centuries of exposure to external influence it would not be 
surprising if the grains had been completely destroyed. Such, however, 
is not the case, and although there is an absence of the proper organic 
elements still the mineral constituents are present, the original form is 
preserved, and each grain is of a blackish-brown colour, and weighs about 
18 milligrammes. In resuming his remarks, M. de Luca observes, “ The 
corn of Pompeii, although preserving its primitive form, has lost all trace 
of organic materials, and contains neither gluten, starch, sugar, nor fatty 
matter. The result of decomposition is such, that there is still found all 
the nitrogen and nearly all the carbon of ordinary corn ; but the mineral 
matters, which I detected in large proportion, were probably due to water, 
which, holding them in suspension, deposited them in the carbonized, 
permeable and amorphous portion of the grains. ,, 
Action of re- Agents on Minerals. — M. Kuhlmann, following up his 
researches on “ the preservation of materials employed in building and 
ornamentation,” has delivered a lecture before the Academy on the above 
subject. Oxygen , he says, gives a brown or bright red colour to green or 
yellow jaspers ; it renders transparent, smoked quartz, amethysts, and 
topazes ; it gives a paler hue to the emerald and sapphire. It deprives red 
and yellow cornelian of their colour, but their silica becomes whitish from 
losing its water of crystallization. Binoxide of nitrogen produces nearly 
the same effect as oxygen. Chlorine is like the preceding gases. The 
diamond, ruby, and sapphire alone resisted its action. By chlorine and 
