WATER. 



(h.) Water and acids, especially the more powerful, render the 

 compound more permanent : if the liquid has begun to effervesce by 

 heat, a drop of the stronger acids, and even of the principal vegeta- 

 ble acids, will cause it to cease, and the addition of an alkali will 

 cause the effect to be renewed. 



(i.) Peroxide of hydrogen is decomposed by heating carefully the 

 diluted solution: its composition as ascertained by its discoverer, 

 Thenard, is hydrogen 1 proportion and oxygen 2 = 16, and 17 is there- 

 fore its representative number. From its great specific gravity, it 

 sinks in common water as sulphuric acid does, although it has a great 

 affinity for that fluid. 



Thenard suggested an application of it to remove dark spots from 

 pictures, in which white lead paint had become tarnished by sulphuret- 

 ted hydrogen : this it effected instantly by the agency of the oxygen of 

 the oxygenized water, which converted the sulphuret into a sulphate. 



Many other particulars might be added respecting this curious com- 

 pound, but they would be inconsistent with the extent of this work. 

 There does not appear any positive proof that the combination of the 

 oxygen is with the hydrogen directly, rather than with the entire water, 

 but the fact that the oxygen bears a multiple relation to that contained 

 in water, affords a strong presumptive proof; perhaps a satisfactory 

 one, in support of the former view. 



EUDIOMETRY BY HYDROGEN. 



Eudiometry has been already mentioned in giving the history of 

 the atmosphere, and it remains to describe, as fast as we come to 

 them, the action of the various substances that operate to remove 

 oxygen from the air, or from any mixture of gases. Hydrogen is 

 one of the most effectual. 



1 . Modes of application. 



(.) In a common eudiometer tube. This kind of tube is 

 made very stout, as in the annexed figure : the glass is well . .. 

 annealed, its mouth is usually trumpet shaped, it is graduated 

 and furnished, towards the top, with two wires, cemented into 

 the glass, and approaching, but not touching each other. In 

 this manner, an electric spark is easily made to pass through 

 the mixed oxygen and hydrogen gases, and an explosion and 

 diminution of volume follow. 



(b.) Dr. lire's eudiometer, of which a figure is 

 annexed, is very simple. It is a syphon tube, clos-. 

 ed at one end, and with platinum wires hermetically 

 inserted : it is of course graduated : its legs are both 

 from six to nine inches long, and the interior diame-. 

 ter is from two to four tenths of an inch : it will receive 

 safely one fourth of an inch of the mixed oxygen 

 and hydrogen gases, and nearly an equal volume of 

 olefiant gas mixture : the water or mercury in the 



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