CHEMICAL SCIENCE. 255 



the same time with water, the decomposition extended to as much as one- 

 third of the mass. Two specimens of glass, having the following compo- 

 sition : 



Silica, 72-1 77-3 



Soda, 12-4 163 



Lime, 15-5 64 



Alumina, i 



Peroxide of iron, } traces - traces " 



were subjected to the same treatment. 



The substance extracted from the first, amounted to" 1.5 per cent.; that 

 from the second, to 2 per cent. ; and, judging from the quantity of lime dis- 

 solved, and the amount of this base in the glass, the decomposition 

 amounted in the one instance to 10 per cent., and in the second to 33 per 

 cent. ; so that glass in which the amount of lime is large in proportion to 

 that of soda, is less decomposed by water than glass in which the amount 

 of lime is less than that of soda. 



The experiments show that it is chiefly the basic constituents of glass that 

 are extracted by water, and probably they might be entirely separated when 

 the action was continued for a long time. 



All ordinary kinds of glass undergo gradual decomposition, when exposed 

 in fine powder to the atmosphere ; they absorb carbonic acid, and after a 

 time effervesce copiously. 



When a mixture of powdered glass and water is exposed for some days to 

 the air, it effervesces with acids, and the solution always contains sulphuric 

 acid, originating from sulphate of soda, which Prof. Pelouze has found in 

 most kinds of glass to the extent of from 0.001 or 1.002 to 2.0 per cent. 



Powdered glass boiled with water, through which a current of carbonic 

 acid is passed, yields a liquid that effervesces copiously with acids. When 

 boiled with solution of sulphate of lime, a considerable amount of sulphate 

 of soda is produced. This reaction accounts for the fact, that the walls and 

 floor of the rooms in which plate-glass is polished, are covered with an 

 efflorescence of sulphate of soda. The gypsum used for fixing the plates 

 yields the sulphuric acid, and the glass yields the soda. 



The extent to which powdered glass is decomposed by water is remark- 

 able, when compared with the great durability of glass vessels under the 

 same condition; and is probably owing to the greater extent of surface 

 offered by the powdered glass to the decomposing influence of the water. 



ON THE USE OF THE MAGNETIC CARBIDE OF IRON FOR THE PURI- 

 FICATION OF WATER. 



The efficacy of oxygen gas in the destruction of every sort of impurity in 

 water has long been known, but the means of readily availing ourselves of 

 this property has been a great desideratum. Profs. Brande and Spencer, of 

 England, recommend the use of the ferroso-ferric carbide of iron, or mag- 

 netic carbide of iron, as a peculiarly rapid and effective mechanical filter, 

 which also possesses the additional valuable property of attracting oxygen 

 to its surface in the form of ozone, which energetically manifests its presence 

 by the exhibition of its wonderful chemical powers of purification. When 

 water is passed through a filter made of this substance, it is deprived of all 

 color, taste, and smell, and nearly all the deleterious gases it may contain 

 (such as sulphuretted and phosphoretted hydrogen) are forced to combine 



