FOREIGN CORRESPONDENCE. 561 



&c., have an equal tendency to consumption, owing to the detritus constant- 

 ly floating in the atmosphere where they work. Work-shops ought to be, 

 according to Dr. Lagneau, subjected to as severe surveillance as lodging 

 houses and hospitals, to prevent over-crowding; all access should be given, 

 not only to air, but to light, and in schools as much importance ought to 

 be devoted to gymnastics, as to intellectual pursuits, and more time for re- 

 creation. Singing societies ought to be established in country towns, and 

 every effort made to encourage manly exercises and healthful amusements, 

 to wean provincials from their tendency to come and live in cities — those 

 "gulfs of humanity," as J. J. Eosseau designated them. 



The air is fourteen and a half times heavier than hj^drogen gas — the 

 latter being the lightest of all known bodies, hence, why it is selected for 

 filling balloons. In practice, however, pure hydrogen is superceded by coal 

 gas on account of its greater cheapness, and because it is always ready pre- 

 pared. But coal gas is heavier than hydrogen, so. that the economical pre- 

 paration of the latter, is an important matter for aeronauts. One of the 

 wonders of next year's exhibition will be a monster balloon by M. Giffard, 

 cubing 20,000 yards ; it will be filled with pure hydrogen ; during the sum- 

 mer he has been experimenting how to jDroduce pure hydrogen not only 

 cheapl}", but in large quantities ; he has emploj^ed two furnaces, of fire- 

 proof clay; the lower one filled with coke, the upper with fragments of 

 natural oxide of iron. The coke being incandescent, the oxide of carbon 

 generated, is conveyed by tubing, over the oxide of iron ; the latter yields 

 its portion of oxygen to the oxide of carbon, and thus forms carbonic acid 

 which escapes into the air; the iron remains pure. Through the latter a 

 jet of steam is passed; the iron seizes the oxygen of the vapor, and the hy- 

 drogen, that other element of water, passes into a refrigerator, and is dried 

 over a bed of chalk. M. Giffard prefers rather the old process for obtaining 

 hydrogen : he lines a boiler with lead, on which sulphuric acid, in the cold 

 state, has no action ; the bottom of the boiler is double, one being perfora- 

 ted, and through which a solution of the acid is introduced to act upon iron 

 clippings; hydrogen is thus produced in great abundance; the sulphate of 

 iron, hitherto an obstacle, is run off into a reservoir. It is this " wet pro- 

 cess " of producing hydrogen that will be employed to inflate the giant 

 balloon next year. 



The project of creating a sea in the interior of Algeria, may be consid- 

 ered as abandoned ; after being weighed in the balances by the Academy 

 of Sciences, it has been found wanting. But this does not the less redound 

 to the credit of Captain Roudaire, who has sacrificed his health and fortune 

 to the survey of the projected canal of some 110 miles, to flood the desert, 

 and make the Sahara blossom like the rose. Tie has also had the warm 

 support of M. de Lesseps in the feasibility of the scheme. The region to 

 be operated upon is the sandy waste situated some 125 miles south of Tu- 



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