MEN 



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M E R 



Cornwall.) An oxide of titanium, or 

 menachine, combined with iron. This 

 substance is found abundantly in the val- 

 ley of Menachan, in Cornwall, and was 

 thus named by its discoverer, Mr. Gregor. 

 It is of a greyish-black colour, and occurs 

 in small grains resembling gunpowder, ol 

 no determinate shape, and mixed with a 

 fine grey sand. Specific gravity 4'4. 

 Before the blow-pipe it neither decrepi 

 tates nor melts. According to the analy 

 sis of Klaproth it consists of oxide of iron 

 51-00, oxide of titanium 45'25, silica 

 3-50, oxide of manganese 0'25. 



ME'NILITE. (from Menil-montant, near 

 Paris, where it is found.) The Menilit 

 of Werner ; Silex menilite of Brongniart ; 

 Quartz resinite subluisant of Haiiy. A 

 brown or yellowish-grey tuberose variety 

 of uncleavable quartz. Menilite occurs 

 in small irregular or roundish masses, 

 often tuberose, or marked with little 

 ridges on its surface. It is translucent, 

 often only at its edges. Structure rather 

 slaty ; fracture conchoidal or splintery. 

 It scratches glass. Specific gravity 2' 18. 

 Infusible before the blow-pipe. Con- 

 stituents, silica 85'5, alumine 1"0, lime 

 0*5, oxide of iron 0*5, water and carbona- 

 ceous matter ll'O. 



MENI'NGES. (from prjviyZ, Gr. a mem- 

 brane.) A name given to the membranes 

 which cover the brain. 



MENI'SCUS. (from fjuqviaicog, Gr.) A lens, 

 one of whose surfaces is convex and the 

 other concave, and in which the two sur- 

 faces meet if continued. As the convexity 

 exceeds the concavity, a meniscus may be 

 regarded as a convex lens. 



ME'NSTRUUM. A solvent. 



MEPHI'TIC. (mephitis, Lat.) Offensive 

 to the smell ; noxious ; pestilential. 



MEPHI'TIC A'CID. Another name for car- 

 bonic acid. 



MEPHI'TIC AIR. Another name for nitro- 

 gen gas. 



ME'RCURY. (mercure, Fr. mercurio, It.) 

 One of the fifty-five simple or elementary 

 bodies. This metal is of the same colour 

 as burnished silver ; when pure and fluid, 

 it is still opaque, and nearly silver-white, 

 with a strong lustre. Its specific gravity 

 is 13-56, or thirteen times and a-half 

 heavier than water, its density being next 

 to those of platinum and gold. Mercury 

 fuses at a temperature of 39 or 40 below 

 the zero of Fahrenheit, that is, at a tem- 

 perature of 71 below the freezing point 

 of water Mercury, which when exposed 

 to a lower temperature is a solid body, 

 becomes fluid : consequently under com- 

 mon circumstances we always find it fluid, 

 and in this respect it remarkably differs 

 from all the other metals. It has obtained | 

 its name from its fluidity and colour. The ! 



boiling point of mercury is somewhere 

 about 680, at which temperature it is con- 

 verted into vapour of a highly expansive 

 power ; this vapour may be again con- 

 densed into the fluid metal, by being re- 

 ceived into cold vessels. Geoffrey in- 

 closed a quantity of mercury in an iron 

 globe, strongly secured by iron hoops, and 

 put the whole into a furnace ; soon after 

 the globe became red-hot it burst with 

 the violence of a bomb, and all the mer- 

 cury was dissipated. 



Mercury has less affinity for oxygen 

 than most other metals ; it may be dis- 

 tilled over five hundred times, without 

 loss of quantity. It combines, however, 

 with oxygen in two proportions, forming 

 a red and a black oxide. By merely 

 heating these in a retort the oxygen may 

 be driven off, and the metal once more 

 obtained in its pure state. 



The existence of mercury, even in small 

 quantities, in any of its ores, may be as- 

 certained by mingling the ore with iron 

 filings, and heating this mixture to red- 

 ness under any cold body, as a plate of 

 polished copper ; the mercury is vola- 

 tilized, and condensed in minute globules 

 on the plate. In consequence of the vo- 

 latility of mercury, it is usually purified 

 by distillation. 



Two of the combinations of mercury 

 with chlorine form most valuable and 

 important medicines ; the one called 

 chloride of mercury, or calomel, the other 

 bichloride of mercury, or corrosive subli- 

 mate. From the fluid state in which 

 mercury exists, it readily combines with 

 most of the metals, to which, if in suffi- 

 cient quantity, it imparts a degree of 

 fusibility or softness : these compounds 

 are termed amalgams. An amalgam of 

 mercury and tin is employed for silvering 

 the backs of looking-glasses, and an 

 amalgam of four parts of mercury, two 

 of bismuth, one of lead, and one of tin, is 

 used for silvering the inside of glass 

 globes, the amalgam fusing on the globe 

 being placed in hot water. The ready 

 combination of mercury with gold or sil- 

 ver, and the facility with which it may be 

 again separated from them by heat, ren- 

 ders it of great value in the obtaining 

 those metals from their ores and alloys in 

 the operations of mining. 



Mercury is also most useful in the con- 

 struction of barometers and thermome- 

 ters. It was known in the remotest ages, 

 and seems to have been employed by 

 the ancients in gilding, and in separating 

 gold from other bodies, as in the present 

 day. It possesses neither taste nor smell. 

 Native mercury occurs in small globules, 

 disseminated in other metals. These 

 globules are but feebly united to their 



