Action of Water upon Glass. 261 



for some hours; upon being allowed to cool, and subside, the 

 clear portion was decanted and evaporated, and became strongly 

 alkaline to the taste, and to other usual tests ; a drop of its con- 

 centrated solution, gradually evaporated on a glass plate, on ex- 

 posure to the atmosphere, in a short time became deliquescent. 

 Tartaric acid produced an effervescence, and afterwards a preci- 

 pitate in this solution ; as likewise did muriate of platinum. 

 From these experiments, therefore, it may be fairly inferred 

 that the alkali removed from the glass was potash in an uncom- 

 bined state, and that the alkaline effect observed in the first in- 

 stance did not depend upon the presence of any alkaline salts, or 

 combination, adhering to or diffused throughout the glass. 



The remaining sediment from the above solution, after having 

 been repeatedly washed in successive portions of water, became 

 inert as to its action on test-papers, not affecting their colours in 

 the slightest degree; but, upon trituration, its alkaline power 

 was again developed ; this property being evidently dependent 

 upon the exposure of a new or undecomposed surface. A slight 

 application of heat to the water, was found greatly to facilitate 

 this evolution of alkali. 



In order to determine the quantity of alkaline matter abstracted 

 from a given weight of glass, by long and continued boiling, 100 

 grains of flint-glass, in fine powder, were boiled nearly every day 

 for some weeks, in two or three successive portions of water ; 

 after this process, the insoluble residue was found deficient in 

 weight by nearly 7 grains. This result, however, must not be 

 considered as accurate, but as a mere approximation ; for, on the 

 one hand, small portions of glass might have been carried away 

 in the supernatant liquor; and, on the other, more alkali might 

 have been abstracted by repeatedly triturating during the process, 

 which, under these circumstances, would be almost unlimited. 



To some pure dilute muriatic acid was added very fine flint- 

 glass, in powder, till it was completely neutralized by its alkaline 

 effect. Upon being allowed to subside, (which, however, was not 

 very readily effected, minute particles remaining suspended for 



