376 Royal Institution. 



sphere will set the silica free from the water-glass, and the silica, 

 thus separated, will be deposited within the pores and around the 

 particles of the stone. The points of contact of these particles will 

 thus be enlarged, and a sort of glazing of insoluble silica will be 

 formed, sufficient to protect the stone against the effects of moisture, 

 &c. This cnuse of i)rotection applies chiefly to sand-stones. But 

 wherever carbonate of lime or carbonate of magnesia enters notably 

 into the composition of the building-stone, then an additional 

 chemical action, also protective of the stone, is expected to take 

 place between these carbonates and the water-glass. Kuhlmann 

 remarks, " Toutes les fois que Ton met en contact un sel insoluble 

 avec la dissolution d'un sel dont I'acide peut former avec la base du 

 sel insoluble un sel plus insoluble encore, il y a echange ; mais le 

 plus souvent cet echange n'est que partiel*." In consequence of 

 this " partial exchange " an insoluble salt of lime may be looked for 

 whenever a solution of water-glass is made to act on the carbonate 

 of lime or carbonate of magnesia existing in oolitic or dolomitic 

 building-stones. 



This expectation, however, has not been altogether sanctioned by 

 experiment. A gentleman, eminently conversant with building 

 materialsf, immersed a piece of Caen-stone in a solution of silicate 

 of potash in the month of January 1849. This fragment, together 

 with a portion of the block from which it had been separated, was 

 placed on the roof of a building in order that it might be fully 

 exposed to the action of atmosphere and climate. After five years 

 the silicated and the uiisilicated specimens were found to be both 

 in the same condition, both being equally corroded. These specimens 

 were exhibited in the Theatre of the Institution. But whatever 

 ultimate results may ensue from this process, the immediate effects 

 on the stone are remarkable. Two portions of Caen-stone were 

 exhibited, one of which had been soaked in a solution of water- 

 glass two months before. The surface of the unsilicated specimen 

 was soft, readily abraded when brushed with water, and its calca- 

 reous ingredients dissolved in a weak solution of sulphurous acid. 

 The silicated surface, on the other hand, was perceptibly hard, and 

 resisted the action of water and of dilute acid when similarly applied:j:. 



II. Another proposed use of the water-glass is that of hardening 

 cements, mortar, &c., so as to render them impermeable by water. 



Fourteen years since Anthon§ of Prague proposed several applica- 

 tions of the water-glass. Among others he suggested the rendering 

 mortars water-proof. He also suggests that this substance might 



• Expe'rienccs Chimiques et Agrononiiques, p. 120. 



t Charles H. Smith, Esq., one of the authors of the ' Report on the Se- 

 lection of Stone for the Building of the New Houses of Parhament.' 



X Silliman's American Journal, January, 185-1, contains a notice of the 

 apphcation of the water-{.dass to the decaying surfaces in the Cathedral of 

 Notre Dame in Paris. 



§ Neuere Mittheilungen iiber die Nutzauwendung dcs Wasser-Glases, 

 1840. This subject has also been fully treated by Kuldmann in his ' Me- 

 moire sur 1' Intervention de la potas';e ou do la sonde dans la formation des 

 chaux hydraidiqiies,' &c., 1841. — Eicpc'riences Chimiqvps et Agrniwmiqvef. 



