1854.] OF THE ROYAL INSTITUTION. 423 
It is true that good stone resists these sources of injury for an 
indefinite time, but such a material is rarely obtained. As a pre- 
ventive of destruction, whether arising from physical or chemical 
causes, it has been proposed to saturate the surfaces of the stones 
with a solution of the water-glass. 
It is well known that the affinity of silica for alkali is so feeble 
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 silication of stone, the carbonic acid of the atmo- 
sphere wiil 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 sand- 
stones. But wherever carbonate of lime or carbonate of mag- 
nesia 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 l’on met en 
contact un sel insoluble avec la dissolution d’un sel dont l’acide 
peut former avec la base du sel insoluble 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 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 
materials,} immersed a piece of Caen-stone in a solution of silicate 
of potass 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 unsilicated 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.} 
* Expériences 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.” 
t Silliman’s American Journal, January, 1854, contains a notice, of the appli- 
cation of the water-glass to the decaying surfaces in the Cathedral of Notre 
Dame in Paris. 
H 
