118 LIMESTONE 



Anhydrous lime, or, as it is commonly called, ' quicklime,' is an amorphous solid, 

 varying much in coherence, according to the kind of rock from which it is obtained ; 

 its specific gravity varies from 2'3 to 3. Lime is one of the most infusible bodies 

 which we possess ; it resists the highest heats of our furnaces. 



When exposed to air, quicklime rapidly absorbs water and crumbles into a powder, 

 commonly known as slaked lime, which is a hydrate of lime. 



Hydrate of lime, when exposed to tlio air, absorbs carbonic acid, and after long ex- 

 posure it is converted into a mixture of carbonate of lime and hydrate of lime in single 

 equivalents. Hydrate of lime is but slightly soluble in water, 729 to 733 parts of that 

 fluid dissolving only 1 part of the lime at ordinary temperatures. 



Hydrate of lime is applied to numerous purposes in the arts and manufactures. It 

 is chiefly employed in the preparation of mortar for building purposes. See MORTAR. 



The pure limes, prepared from the carbonates of lime, form an imperfect mortar 

 suitable only for dry situations. In damp buildings or in wet situations they never 

 set (as the process of hardening is technically termed), but always remain in a pulpy 

 state. General Pasley says, ' The unfitness of pure lime for the purposes of hydraulic 

 architecture has been proved by several striking circumstances that have come under 

 my personal observation, of which I shall only mention a few. First, a great portion 

 of the boundary -wall of Rochester Castle having been completely undermined, nearly 

 throughout its whole thickness, which was considerable, whilst the upper part of the 

 same wall was left standing, I had always ascribed this remarkable breach to violence, 

 considering it as having been the act of persons intending to destroy the wall for the 

 sake of the stone ; but on examining it more accurately after I had begun to study 

 the subject of limes and cements, I observed that the whole of the breached part was 

 washed by the Medway at high water, and that all the mortar of a small portion of 

 the back part of the foot of the wall still left standing was quite soft, but that towards 

 the ordinary high water level it became a little harder, and above that level it was 

 perfectly sound. I observed the same process at the outer wall of Gockham Wood 

 Fort, on the left bank of the Medway, below Chatham, of which the upper part was 

 standing, whilst the lower part of it had been gradually ruined by the action of the 

 river at high water destroying the mortar.' The peculiar conditions necessary to 

 insure a good and useful mortar for building purposes, and the peculiarities of the 

 hydraulic mortars or cements are treated of under HYDRAULIC CEMENTS and 

 MORTAB. 



LIMESTONE. (Calcaire, Fr. ; Kalkstein, Ger.) A great variety of rocks contain 

 a sufficient quantity of carbonate of lime to be called limestones. 



Chalk is an earthy massive opaque variety, usually soft and without lustre, and may 

 be regarded as a tolerably pure carbonate of lime. Carbonate of lime dissolves in 1,000 

 parts of water charged with carbonic acid. (Bischof.) Fresenius states that it dissolves 

 in 8,834 parts of boiling water and in 10,601 parts of water at ordinary temperatures. 



Carbonate of lime is found in nature more or less pure ; it occurs crystallised, as 

 in calcspar and aragonite ; and also occurs as granular limestone ; and in compact 

 masses, as in common limestone, chalk, &c. 



Stalactitic carbonate of lime, frequently called concretionary limestone, is formed by 

 the infiltration of water through rocks containing lime, which is dissolved out, and as 

 it slowly percolates the rocks into cavernous openings, the water parts with its carbo- 

 nate of lime, which is deposited in zones more or less undulated, which have a fibrous 

 structure from the crystalline character of the concretionary lime. The long fibrous 

 pieces called stalactites show those fibres very beautifully. The stratiform masses 

 called stalagmites exhibit a similar structure, varied only by the conditions under 

 which they are formed. A very remarkable stalagmitic limestone found in Egypt is 

 known as oriental alabaster. 



True Alabaster is a sulphate of lime, but the stalagmitic carbanate is not unfre- 

 quently called by this name. See ALABASTER. 



Incrusting concretionary limestones differ but little from the above. They are deposits 

 from calcareous springs which are common in some parts of Derbyshire, Yorkshire, 

 and other places. It is a common practice to place vegetable substances in those 

 springs ; they then become incrusted with carbonate of lime, and are sold as petrifac- 

 tions, which they are not. In volcanic districts many very remarkable springs of 

 this character exist. One of the most remarkable is at the baths of San Filippo, 

 in Tuscany, where the water flows in almost a boiling state ; carbonate of lime here 

 appears to be held in solution by sulphuretted hydrogen, which flies off when the 

 water issues to-day. Dr. Vegny has taken advantage of this property of the spring 

 to obtain basso-rilievo figures of great whiteness and solidity by occasioning the lime 

 to deposit in sulphur moulds. 



Agaric mineral, Spongy limestone, Bock milk, is found at the bottom of and about 



