220 MARLSTONE 



of yellow, steel-grey, and rose-coloured spots. That of Bergamo consists of black and 

 grey fragments in a greenish cement. Florence marble, called also ruin and land- 

 scape marble, is an indurated calcareous marl. 



Sicily abounds in marbles, the most valuable of which is that called by the English 

 stone-cutters Sicilian jasper ; it is red, with large stripes like ribands, -white, red, and 

 sometimes green, which run zigzag -with pretty acute angles. 



Of Cutting and Polishing Marble. The marble-saw is a thin plate of soft iron, 

 continually supplied during its sawing-motion with water and the sharpest sand. 

 The sawing of moderate pieces is performed by hand, but that of large slabs is most 

 economically done by a proper mill. 



The first substance used in the polishing process is the sharpest sand, with which 

 the marble must be worked till the surface becomes perfectly flat. Then a second, 

 and even a third sand of increasing fineness is to be applied. The next substance 

 is emery of progressive degrees of fineness, after which tripoli is employed ; and the 

 last polish is given with tin-putty. (See PUTTY-POWDER.) The body with which 

 the sand is rubbed into the marble is usually a plate of iron ; but for the subsequent 

 process, a plate of lead is used with fine sand and emery. The polishing-rubbers are 

 coarse linen cloths, or bagging, wedged tight into an iron planing-tool. In every step 

 of the operation a constant trickling supply of water is required. 



IVSARCASITE, or white iron pyrites, is of a pale bronze-yellow, or iron-grey 

 colour, with a metallic lustre. It is a bisulphide of iron, composed of iron 46'7, sul- 

 phur 63-3. Specific gravity 4-678 to 4-847. 



The mineral was formerly much used for various ornaments, as shoe- and knee- 

 buckles, pins, bracelets, setting of watch-cases, &c. ; and, although the taste for it 

 has considerably declined now, probably owing in some degree to its abundance, 

 immense quantities are still cut and manufactured at Geneva and in the French Jura. 



The marcasite of commerce is generally small, rarely attaining the size of a stone 

 of two carats. It takes a good polish, and is cut in facets like rose-diamonds. In 

 this state it possesses all the bright blue of polished steel, without the tendency of 

 the latter to become oxidised by exposure to the action of the atmosphere. It is prin- 

 cipally procured from Germany and the Jura. H. W. B. See PYRITES. 



IYIARCASITE. Bismuth was formerly so called. See BISMUTH. 



IVIARGARATES are saline compounds of margaric acid with the bases. 



IVIARGARIC ACID (Margarine) is one of the acid fats produced by saponify- 

 ing tallow with alkaline matter, and decomposing the soap with dilute acid. The 

 term margaric signifies pearly-looking. 



The physical properties of the margaric and stearic acids are very similar ; the chief 

 difference is that the former is more fusible, melting at 140 Fahr. The readiest mode 

 of obtaining pure margaric acid is to dissolve olive-oil soap in water, to pour into the 

 solution a solution of neutral acetate of lead, to wash and dry the precipitate, and then 

 to remove its oleato of lead by ether, which does not affect its margarate of lead. The 

 residuum being decomposed by boiling-hot muriatic acid, affords margaric acid. When 

 heated in a retort this acid boils. It is insoluble in water, very soluble in alcohol and 

 ether ; it reddens litmus-paper, and decomposes, with the aid of heat, the carbonates 

 of soda and potash. 



Margaric acid is obtained most easily by the distillation of stearic acid. The 

 humidity at the beginning of the process must be expelled by a smart heat, otherwise 

 explosive ebullitions are apt to occur. Whenever the ebullition becomes uniform, the 

 fire is to be moderated. See OILS. 



MARINA. A name given to madder after it has undergone a peculiar treatment. 

 See Crookes's ' Handbook of Dyeing.' 



MARINE ACID. Hydrochloric acid was formerly so called because it could 

 be obtained from sea-water. See HYDROCHLORIC ACID and MURIATIC ACID. 



MARINE METAXi. A name for Wetterstedt's alloy, which was introduced as 

 a sheathing for ships. It consisted of lead 94'4, antimony 4 - 3, and mercury 1'3. It 

 was said not to be attacked by sea-water, and to remain free from vegetable or animal 

 growth. 



MARINE SAX.T. See SALT. 



MARJORAM. The Origanum majorana, one of the Labiata, is used as an 

 aromatic herb, and yields oil ofmarjoram on distillation. 



MARK (Marne, Fr. ; Mcrgel, Ger.) is a mixed earthy substance, consisting of 

 carbonate of lime, clay, and siliceous sand, in very variable proportions ; it is 

 sometimes compact, sometimes pulverulent. According to the predominance of 

 one or other of these ingredients, marls are distributed into calcareous, clayey, and 

 sandy. 



MARX.STONE. One of the members of the Lias formation. The Cleveland 

 iron ore occurs in the marlstonc, or middle lias. See LIAS. 



