Buarr.—On the Building Materials of Otago. 127 
compact than sandstone, it absorbs more water; but, on the other hand, 
the water affects it much less than sandstone. The compactness of lime- 
stone seems to keep the water from freezing, and so neutralizes its most 
powerful disintegrating property. All the softer limestones are hardened 
by exposure to the atmosphere; at the same time the atmosphere contains 
the elements of their destruction. The indurating process is not, as is some- 
times supposed, attributable to the absorption of carbonic acid from the 
atmosphere, like the setting of mortar. The lime in the stone, being 
already a carbonate, cannot in this way absorb more of the acid. The 
hardening on exposure is caused entirely by the evaporation or drainage of 
the moisture contained in the pores of the stone. 
The ingredients in the atmosphere that have the most deleterious effect 
on stones are muriatic and sulphuric acid, both of which have an affinity 
for lime, and combine readily with it, thus rendering the stone soluble in 
water. The former acid is always present in the atmosphere near the sea, 
and the latter in manufacturing towns, where coal is burnt. All the softer 
limestones are more or less subject to the pernicious effects of both these 
acids, and when magnesia enters into their composition, they are particu- 
larly susceptible to the action of sulphuric acid. The English Houses of 
Parliament are built of magnesian limestone, from the Bolsover quarries in 
Derbyshire—its composition being as follows :— 
Bilita  .:. Zan Rees ie eae 8.6 
Carbonate of lime ay et a SOLE 
Carbonate of magnesia... ie ey. 
Tron alumina ... enh ot ee 1.8 
Water and loss ... es fae cee 8.8 
100.0 
It is well known that this stone has been a decided failure ; the build- 
ings were not many years finished when they began to show symptoms of 
decay. This result is due entirely to the sulphuric acid with which the 
smoky atmosphere in London is impregnated. The selection of the Bolsover 
stone for such an important work is perhaps the most curious instance on 
record of the miscarriage of skill, experience, and good intention. The 
English Government, fully alive to the necessity of having the Houses of 
Parliament built of the best stone procurable, appointed a Scientific Com- 
mission for the purpose of enquiring into the qualities of the various build- 
ing stones in Great Britain. The Commissioners were men of the highest 
standing, whether as regards their disinterestedness or scientific attain- 
ments ; they had carte blanche to examine, enquire into, and experiment on 
every stone in the kingdom, in short their instructions appear to have 
