MET 



MET 



middle, secondary rocks ; they vary in 

 width from an inch, or less, to several 

 yards, and sometimes extend to many 

 miles. These veins, unlike metallic de- 

 posits, -were formed at periods subsequent 

 to the formation of the rocks in which 

 they occur. 



METALLO'GRAPHY {fiiraWov, a 

 metal, ypdcpa, to describe). That branch 

 of science which treats of metals. 



ME'TALLOID (neTaWov, a metal, 

 eidos, likeness). A term applied, at first, 

 to the metals obtained from the fixed 

 alkalies and some of the earths. The 

 term is sometimes applied to the inflam- 

 mable non-metallic bodies, as sulphur, 

 phosphorus, &c. 



METALLU'RGY (/ueraWov, a metal, 

 epyov, work). The separation of metals 

 from their ores, comprising the opera- 

 tions of assaying, refining, smelting, &c. 



ME'TALS (/uexaWov/, a mine ; a mine- 

 ral; a metal). A class of elementary 

 bodies, most of which are characterized 

 hy their peculiar metallic lustre, and, 

 generally speaking, by their great specific 

 gravities. They are divided into different 

 classes, according to their affinity for oxy- 

 gen, and the peculiar properties of their 

 various oxides. They are distinguished 

 as : — 



1. Perfect Metals. Those which com- 

 bine with difficulty with oxygen, and 

 consequently are not easily oxidized ; as 

 such, they readily part with oxygen by 

 the simple application of heat, and are 

 converted into pure metals. The best 

 known are platinum, gold, and silver. 

 Mercury holds an intermediate place be- 

 tween these and the next class. 



2. Base Met ils. Those which readily 

 combine with oxygen, partly by mere 

 contact with the atmosphere, or when 

 heated and fused. They are not reducible 

 by the application of heat only, but re- 

 quire the admixture of some substance, 

 as coal, to attract the oxygen from the 

 oxide. The best known are iron, copper, 

 lead, tin, and zinc. The metals com- 

 posing this and the preceding class are 

 termed, from their great specific gra- 

 vities, the heavy metals. 



3. Acidifying Met'ils. Those which, 

 entering into combination with oxygen, 

 possess the property of acids, which are 

 hence called metallic acids. These metals 

 are tellurium, arsenic, chromium, mo- 

 lybdenum, tungsten, columbium, and 

 selenium. 



4. Terrigenous Metals. Those whose 

 oxides yield the earths, properly so called. 



217 



They resist the action of heat, and are 

 insoluble in water. These are aluminum, 

 yttrium, cerium, lantanum, thorium, 

 glucinum, and zirconium. 



5. Kaligenous Metals. Those which 

 oxidize most readily, their oxides consti- 

 tuting the alkalies. These are magne- 

 sium, calcium, strontium, barium, li- 

 thium, sodium, and potassium. As the 

 metals of this and of the preceding class 

 are some lighter and others but little 

 heavier than water, they are called light 

 metals. 



METAME'RIC (juera, a preposition 

 denoting change, nepoi, a part). A term 

 applied to compounds in which the ulti- 

 mate elements are the same as in other 

 well-known combinations, but are con- 

 sidered to be arranged in a diflTerent way : 

 thus, oxygen, hydrogen, sulphur, and a 

 metal, may be considered as combined in 

 the form of sulphuretted hydrogen and a 

 metallic oxide, or of water (consisting of 

 oxygen and hydrogen) and a metallic 

 sulphuret. See Isomeric and Polymeric. 



METAMO'RPHIC {nera, a preposi- 

 tion denoting change, /JLopcprj, form). A 

 term applied by Mr. Lyell to the series 

 of crystalline slates which occurs espe- 

 cially in the central ridges of mountain 

 chains. The term denotes that their 

 structure has been changed, since the 

 time of their first formation, by plutonic 

 action. See Hypozoic System. 



METAMORPHO'SIS (/uera, a prepo- 

 sition denoting change, and fxopcpr], form). 

 Literally, a change of form. A term em- 

 ployed by Liebig to denote that chemical 

 action by which a given compound is 

 caused, by the presence of a peculiar 

 substance, to resolve itself into two or 

 more compounds ; as sugar, by the pre- 

 sence of yeast, into alcohol and carbonic 

 acid. 



METAMORPHO'SIS (in Botany). 

 Morphology. These terms denote a the- 

 ory, according to which the several organs 

 of plants are referred to a typical organ, 

 varying in their modes of development, 

 not on account of any original difference 

 in structure, but on account of especial, 

 local, and predisposing causes. In the 

 words of Gothe, the originator of the 

 theory, plants "develop themselves out 

 of themselves progressively." 



METAMORPHO'SIS (in Zoology). A 

 term denoing a series of changes which 

 insects undergo, both in their outward 

 form and their internal structure, before 

 they arrive at their perfect condition. 

 The successive states of existence are 



