302 Intelligeiicc a?id Miscellafiemis Articles. 



water charged with carbonic acid, which, dissolving a portion of the 

 lime of the cement, percolates with it in solution in the form of bicar- 

 bonate, until it reaches the air by arriving on the face of the soffite, 

 when the water and the second atom of carbonic acid evaporate, leaving, 

 wherever the solution has penetrated the joints, a stalactite of carbon- 

 ate of lime. But in some cases where the arches are of brick, or of 

 porous stone, the drainage appears to take place through the substance 

 of the bricks or stones themselves, when stalactites are produced on 

 their exposed surfaces, independently of the joints. And in some cases 

 of this description the lime, or its carbonate, (since the latter becomes 

 soluble in the excess of carbonic acid,) appears to be derived from the 

 stones or bricks themselves, while in others, as just mentioned, it comes 

 from the superincumbent soil. 



In Hill's History of Fossils, (a work which, however antiquated in 

 point of science, as a system of Mineralogy, yet contains some inter- 

 esting and authentic information,) we are informed that stalactites re- 

 sembling those in the caverns of the Mendip Hills, are not unfrequent- 

 ly found hanging down from stone arches, and those such as have not 

 been long built; "eventhearchesof our new bridge over the Thames at 

 Westminster," it is stated, " tho' that building is hardly yet finished, 

 are already hung with small ones." In the same work, another variety 

 of stalactite, frequent in caverns and on the roofs of old mines in the 

 Hartz, is related to have been found in great quantity in a brick vault 

 supporting part of the terrace at Windsor Castle ; the vault being in 

 a manner filled up with it, some stalactites hanging down for manj^ 

 feet in length from the roof, others standing erect on the floor, and 

 others coating the walls. In this case the stalactites hung more from 

 the bricks themselves than from the mortar in thejoints,and they nearly 

 amounted in quantity to that of all the mortar in the vault ; so that the 

 drainage appears to have taken place through the substance of the 

 bricks, and the lime or its carbonate in the stalactites appears to have 

 been derived either from them, or from the superincumbent soil, — 

 most probably, however, from the latter. Hill's History of Fossils, 

 forming the first volume of his proposed General Natural History, 

 London, 1748, fol. p. 36S, 369. 



In the magnificent range of bridges and aqueducts which cross the 

 new cut, as it is called, of the Birmingham Canal, between the Ikenield 

 Street and the village of Oldbury, a few miles from Birmingham, is a 

 brick arch carrying a rivulet, or another branch of the canal, I am un- 

 certain which, over the new cut. In September 1830 I observed on 

 the soffite of the arch a multitude of small stalactites, attached chiefly 

 to the joints, the formation of which was evidently still going on from 

 the drainage through the brick-work. In this case the water of the 

 aqueduct must have furnished the carbonic acid, and the lime must 

 have been derived from the materials used in puddling the aque- 

 duct, or from the mortar of the joints, and in part also from the water 

 itself. 



Sir H. Davy has stated, in his Agricultural Chemistry, Lect. vii. 

 that "when hydrate oflime becomes carbonate of lime by long exposure 

 to air, the water is expelled, and the carbonic acid gas takes its place.'' 



