4 Analysis of native Caustic Lime. [1816. 



OBSERVATIONS ON THE PRECEDING PAPER. 



BY SiRH. DAVY, F.P.R.I., F.R.S. 



THE Duchess of Montrose was so good as to send me the 

 caustic lime which is the subject of the preceding analysis ; 

 her Grace received it immediately from Tuscany, It was in a 

 hottle, carefully sealed and full of water. Some of the exterior 

 portions had become combined with carbonic acid before they 

 were collected, and from the colour, it appeared that there 

 were different portions of protoxide of iron in different parts 

 of the substance. 



On examining the water, it was found to be a saturated 

 solution of lime, and it contained fixed alkali, but in quan- 

 tities so minute, that after the lime was separated, it could be 

 made evident only by coloured tests. 



It appears from Mr. Faraday's analysis, that the menstruum 

 which deposits the solid substance must be a solution of silica 

 in lime-water, and heat is evidently the agent by which the 

 large quantity of lime deposited is made soluble and is enabled 

 to act on silica ; and the fact offers a new point of analogy 

 between the alkalies and the alkaline earths. 



Vestiges of extinct volcanoes exist in all the low countries 

 on the western side of the Apennines ; and the number of 

 warm springs in the Tuscan, Roman, and Neapolitan States, 

 prove that a source of subterraneous heat is still in activity 

 beneath a great part of the surface in these districts. 



Carbonic acid is disengaged in considerable quantities in 

 several of the springs at the foot of the Apennines ; and some 

 of the waters that deposit calcareous matter are saturated 

 solutions of this substance. Calcareous tufas of recent for- 

 mation are to be found in every part of Italy. The well- 

 known Travertine marble, Marmor Tiburtinum, is a pro- 

 duction of this kind ; and the Lago di Solfaterra near Tivoli, 

 of which I shall give a particular account on a future occasion, 

 annually deposits masses of this stone of several inches in 

 thickness. 



It is scarcely possible to avoid the conclusion, that the 

 carbonic acid, which by its geological agency has so modified 

 the surface of Italy, is disengaged in consequence of the 

 action of volcanic fires on the limestone, of which the Apen- 

 nines are principally composed, and liberated at their feet, 



