salt; which enrich it, not only in the centre of Europe, as in Cheshire, at Vic, Wieliczka ,Bochnia, and Salzbourg , bnt in many other parts of the world.
The lias contains often very pyritous lignites, which are mined in many places, andparticularly at Whitby and Guisborough in Yorkshire , for the manufacture of alum andcopperas.
The oolitic limestones contain strata of iron ore, which are mined in some districts ofPrance.
The iron sand (Hastings sand) beneath the chalk formation, is often so strongly im-bued with iron as to be worth the working.
The lowest beds of the chalk contain iron pyrites, which has become the object of animportant exploration at Vissans, on the southern coast of the Pas-dv-Calais, where it isconverted into sulphate of iron. The waves turn the nodules out of their bed, and rollthem on the shore, where they are picked up.
If the chalk be poor in useful minerals, this is not the case with the plastic clay for-mation above it; for it contains important mines. In it are explored numerous bedsof lignite (wood-coal), either as fuel or a vitriolic earth. Prom these lignite deposites,also, the yellow amber is extracted.
The other tertiary formations present merely a few mines of iron and bitumen.
. Several of the secondary or tertiary strata contain deposites of sulphur, which aremined in various countries.
The formations of a decidedly volcanic origin afford few mining materials, if we ex-cept sulphur, alum, and opals.
MINES OP THE ALLUVIAL STRATA.
This formation contains very important mines, since from it are extracted all the dia-monds, and almost all the precious stones, the platinum, and the greatest part of the gold,With a considerable portion of the tin and iron. The diamond mines are confined nearlyto Brazil , and to the kingdoms of Golconda and Visapour in the East Indies.
MORTAR, HYDRAULIC . Professor Kuhlmann, of Lisle, obtained a patent inApril, 1841, in the name of Mr. Newton, for certain improvements in the manufactureof lime-cement and artificial stone; and of which he gave me a sample, possessed of ahardness and solidity fit for the sculptor.
In operating by the dry method, instead of calcining the limestone with sand andclay alone, as has been hitherto commonly practised, the inventor introduces a smallquantity of soda, or, preferably, potash, in the state of sulphate, tarbonate, or muriate ;salts susceptible of forming silicates when the earthy mixture is calcined. The alkalinesalt, equal in weight to about one fifth that of the lime, is introduced in solution amongthe earths.
All sorts of lime are made hydraulic, in the humid way, by mixing slaked lime withsolutions of common alum or sulphate of alumina; but the best method consists in em-ploying a solution of the silicate of potash, called liquor of flints, or soluble glass, to mix'n with the lime, or lime and clay. An hydraulic cement may also be made which Wills dve for the manufacture of architectural ornaments, by making a paste of pulverizedchalk, with a solution of the silicate of potash. The said liquor of flints will likewiseS've chalk and plaster a stony hardness, by merely soaking them in it after they are cutor moulded to a proper shape, On exposure to the air, they get progressively indurated.Superficial hardness may be readily procured by washing over the surface of chalk, &c.," r itii liquor of flints, by means of a brush. This method affords an easy and elegant*hethod of giving a stony crust to plastered walls and ceilings of apartments ; as also tostatues and busts, cast in gypsum, mixed with chalk. •
. The essential constituents of every good hydraulic mortar, are caustic lime andSl lica; and the hardening of this compound under water consists mainly in a chemicalcombination of these two constituents through the agency of the water, producing aJjydrated silicate of lime. But such mortars may contain other bases besides lime, as,or example clay and magnesia, whence double silicates of great solidity are formed;cn which account dolomite is a good ingredient of these mortars. But the silica must
in a peculiar state for these purposes; namely, capable of affording a gelatinous paste?Th acids ; and if not so already, it must be brought into this condition, by calcining
along with an alkali or an alkaline earth, at a bright red heat, when it will dissolve,and gelatinize in acids. Quartzose sand, however fine its powder may be, will form no^ a for mortar with lime ; but if the powder be ignited with the lime, it then becomes fit! 0r hydraulic work. Ground felspar or clay forms with slaked lime no water cement;hut when they are previously calcined along with the lime, the mixture becomes capable° J? ar< lening under water.
0 The mastic called HameKn’s , and so much employed in London , is composed ofS'oond Portland stone (roe stone), sand, and litharge, in the proportion of 62 of therst ; 35 of the second, and 3 of the third, in 100 parts ; but other proportions will also