Scientific Intelligence.—Miscellaneous. 187 
that it may be separated from this base by the weakest acids, 
even by carbonic acid. According to the expectation of those who 
recommend the silification of stone, the carbonic acid of the atmo- 
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 cause of protection applies chiefly to sandstones; but 
wherever carbonate of lime or carbonate of magnesia enters notably 
into the composition of the building stone, then an additional che- 
mical action, also protective of the stone, is expected to take place 
between these carbonates and the water-glass. Kuhlmann remarks, 
‘ Toutes les fois que l’on met en contact un sel insoluble avec la 
dissolution d’un sel dont l’acide peut former avec la base du sel in- 
soluble un sel plus insoluble encore il y a échange; mais le plus 
souvent cet échange n’est que partiel..* In consequence of this 
* partial exchange,’ an insoluble salt of lime may be looked for when- 
ever a solution of water-glass is made to act on the carbonate of 
lime or carbonate of magnesia existing in oolitic or dolomitie build- 
ing stones. 
“ This expectation, however, has not been altogether sanctioned 
by experiment. A gentleman, eminently conversant with building 
materials,; 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 ex- 
posed to the action of atmosphere and climate. After five years the 
silicated and the unsilicated specimens were found to be both in the 
same condition, being both 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 calcareous ingredients 
dissolved in a weak solution of sulphurous acid. The silicated sur- 
face, on the other hand, was perceptibly hard, and resisted the ac- 
tion of water and of dilute acid when similarly applied.’”’} 
* Experiences Chimiques et Agronomiques, p. 120. 
+ Charles H. Smith, Esq., one of the authors of the “ Report on the Selection 
of Stone for the Building of the New Houses of Parliament.” 
{ Silliman’s American Journal, January 1854, contains a notice of the ap- 
plication of the water-glass to the decaying surfaces in the Cathedral of Notre 
Dame in Paris. 
