HYDRAULIC LIME 



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render it necessary to adopt a definite principle of nomenclature in this respect. . . . 

 I shall employ the word hydrate only where the water is combined with a base, such 

 as a metallic oxide, thus, hydrate of lime, hydrate of potash, hydrated oxide of lead.' 

 Kane. 



HYDRAULIC ZiZME. The poorer sorts of limestone, such as contain from 8 to 

 25 per cent, of foreign matter, in silica, alumina, magnesia, &c., form the best hydraulic 

 limes. All the water limestones are of a bluish-grey or brown colour, which is com- 

 municated to them by the oxide of iron. They are usually termed stone-lime by the 

 builders of the metropolis, to distinguish them from common chalk-lime, but so far 

 improperly, that the Dorking limestone is not much harder than chalk, and the Hailing 

 limestone is actually a chalk, and not harder than the pure chalk of the same neigh- 

 bourhood, from which it is only distinguished in appearance by being a little darker. 

 These, though calcined, do not slake when moistened ; but if pulverised they absorb 

 water without swelling up or heating, like fat lime, and afford a paste which hardens 

 in a few days under water, but in the air they never acquire much solidity. 



The following analyses of different hydraulic limestones are by Berthier : 



No. 1 is from the fresh-water lime formation of Chateau-Landon, near Nemours ; 

 No. 2, the large-grained limestone of Paris ; both of these afford a fat lime when 

 burnt. Dolomite affords a pretty fat lime, though it contains 42 per cent, of carbonate 

 of magnesia. No. 3 is a limestone from the neighbourhood of Paris, which yields a 

 poor lime, possessing no hydraulic property ; No. 4 is the secondary limestone of 

 Metz ; No. 5 is the lime-marl of Senonches, near Dreux ; both the latter have the 

 property of hardening under water, particularly the last, which is much used at Paris 

 on this account. 



All good hydraulic mortars must contain alumina and silica; the oxides of iron and 

 manganese, at one time considered essential, are rather prejudicial ingredients. By 

 adding silica and alumina, or merely the former, in certain circumstances, to fat lime, 

 a water-cement maybe artificially formed ; as also by adding to lime any of the follow- 

 ing native productions, which contain silicates ; puzzolana, trass or tarras, pumice- 

 stone, basalt-tuff, or slate-clay. Puzzolana is a volcanic .product, which forms hills of 

 considerable extent to the south-west of the Apennines, in the district of Eome, the 

 Pontine marshes, Viterbo, Bolsena, and in the Neapolitan region of Puzzuolo, whence 

 the name. A similar volcanic tufa is found in many other parts of the world. 

 According to Berthier, the Italian puzzolana consists of 44-5 silica ; 15'0 alumina ; 

 8-8 lime; 4*7 magnesia; 1*4 potash; 4'1 soda; 12 oxides of iron and titanium; 9'2 

 water ; in 100 parts. 



The tufa stone, which when ground forms trass, is composed of 57'0 silica, 16*0 clay, 

 2-6 lime, TO magnesia, 7"0 potash, TO soda, 5 oxides of iron and titanium, 9"6 water. 

 This tuff is found abundantly, filling up valleys in beds of 10 or 20 feet deep, in the 

 north of Ireland, among the schistose formations upon the banks of the Ehine, and at 

 Monheim in Bavaria. 



The fatter the lime the less of it must be added to the ground puzzolana, or trass, to 

 form a hydraulic mortar ; the mixture should be made extemporaneously, and must at 

 any rate be kept dry till about to be applied. Sometimes a proportion of common 

 sand-mortar instead of lime is mixed with the trass. When the hydraulic cement 



