801 



METALS. 



METAMORPHOSIS. 



802 



There are two metals only which are capable of beiug rendered 

 permanently magnetic, namely, iron and nickel ; the former of these 

 only is met with possessing this property in nature ; it is an oxide of 

 iron, and commonly called the Loadstone. Most of the metals com- 

 bine with each other, and form compounds differing very materially in 

 properties from their constituent metals. [ALLOTS.] 



All metals unite with oxygen, but with different degrees of facility 

 and affinity ; most of them combine with more than one proportion 

 of oxygen, and some of them with several proportions. The nature 

 of the compounds formed is extremely various ; thus some metals 

 form with oxygen comparatively inert compounds or mere oxides, 

 such as iron and zinc ; others, such as potassium and sodium, when 

 oxidised become alkalis ; while arsenic and chromium form acids with 

 this element. It has been already observed that some metals unite 

 with several proportions of oxygen, and these may be mere oxides, as 

 in the case of iron ; or oxides and acids, as occurs with manganese ; 

 but there is no case of any metal forming a mere oxide and an alkali 

 with different proportions of oxygen, or an acid and an alkali under 

 the same circumstances. 



Chlorine and metals combine with great facility, and the compounds 

 are extremely important. Every metal is indeed susceptible of this 

 combination ; but chlorine possesses the remarkable property of form- 

 ing in general volatile compounds with the metals. Bromine, sulphur, 

 iodine, and phosphorus, combine with most of the metals. 



The action of the air, of water, and the acids, upon the metals, is 

 extremely various, and depends greatly upon their respective affinity 

 for oxyg'-n. Few of them are oxidised in dry air, but many of them 

 tarnish and some oxidise readily in it when moist, of which iron is an 

 example. Some metals, as potassium, sodium, and manganese, decom- 

 pose water even at common temperatures, combining with its oxygen 

 and evolving the hydrogen ; others, as iron and zinc, require to be 

 strongly heated, or the presence of an acid, to .effect this decom- 

 position. 



Moat of the metals are dissolved by acids, but platina and gold 

 are exceptions, these and some others requiring chlorine, and that 

 generally in the nascent state called aqua regia. Few metala however 

 are acted upon by acids without the presence of water, and in some 

 instances the water, in others the acid, and often both, suffer decom- 

 position ; and it is to be observed that no metal dissolves in acid unless 

 it be either previously oxidised or acquire oxygen from the mixture 

 of acid or water in which the solution takes place. The salts formed 

 ore in many cases of the highest importance in chemical investigations, 

 in the chemical arts, and in medicine. 



Metals are found either native or mineralised by combination with 

 other substances. The common ores are compounds of the metals 

 with oxygen, aulphnr, arsenic, carbonic acid, or silica. For example, 

 the oxides and carbonate of iron are the common workable iron-ores ; 

 Bulphuret of lead (called galena) is the lead-ore of the arts ; arsenical 

 cobalt is the principal source of cobalt and arsenic. Only a few of 

 the metala occur native in the rocks : of these gold, platinum, indium, 

 and rhodium are, with a rare exception, found only native. The 

 bismuth of the shops ia obtained from native bismuth. Native silver, 

 native mercury, and native copper are sometimes abundant, but are 

 far from being the main sources of these metals. The other native 

 metala are mineralogical rarities. Perhaps we should except from 

 this remark native iron, which constitutes large meteoric masses, though 

 very rarely, if ever, seen of terrestrial origin. The ores of the metals 

 are often much disguised by mixture with one another or with earthy 

 materials. Thus a large part of the iron-ore worked in Great Britain 

 ia ao mixed with clay of silica that its real character might not be 

 suspected without some experience in ores. 



Occasionally ores contain phosphate of iron, or some arsenical ores, 

 or certain sulphurets, scattered through them, and on account of the 

 difficulty of separating the phosphorus, sulphur, or arsenic, the ore is 

 rendered comparatively useless. By this intimate mixture of species 

 the difficulties of reducing ores are much increased. When different ores 

 are not ultimately commingled they are frequently closely dissemi- 

 nated together through the rock. We find ores of lead and zinc often 

 thus associated ; also of cobalt and nickel ; of iron and manganese ; 

 the ores of silver, lead, and copper, and often cobalt and antimony ; 

 platinum, iridium, palladium, and rhodium. 



MetaU and their orea occur in the rocks hi different ways : 



1. In beds or layers between layers of rock, as some iron-ores. 



2. Disaeminated through rocks in grains, nests, or crystals, or 

 extei/Wl masses, as is the case with iron pyrites, cinnabar, or mer- 

 cury-ore, and much argillaceous iron. 



3. In veins intersecting different rocks, as ores of tin, lead, copper, 

 and nearly all metallic ores. 



4. Very frequently metallic ores, instead of occurring in true veins, 

 are found in rocka near their intersection with a mass or dyke of 

 igneous rock, aa in the vicinity of a porphyry or trap dyke. This is 

 the case with much of the copper-ore in Connecticut and Michigan, as 

 well as with much silver-ore and mercury in South America, and else- 

 where ; and often the igneous rock itself contains the same metals 

 dimemin^ted through it. 



The rock immediately enveloping the ore is called the Gangue. A 

 Vein often consists for the most part of the rock material called the 

 gangue ; and the ore either intersects the gangue in a continued band, 



HAT. im-r. DIV. VOL. in. 



or more commonly is partly disseminated through it in some places, 

 and is continuous for long distances in others. Often a good vein 

 gradually loses its character, the metal disappears, and the gangue is 

 left; but by following on for some distance it will often resume its 

 former character. The usual gangue in metallic veins is either quartz, 

 calc-spar, or heavy spar ; less frequently fluor-spar. Calc-spar is the 

 gangue of the Bossie lead-ore ; heavy spar of much of the lead-ore of 

 the Mississippi Valley ; fluor-spar, in some places, of the lead of 

 Derbyshire, England. (Dana, ' Mineralogy.') 



The metala which are found pure, as well as the various compounds 

 of metals which occur as minerals, will be found described in this 

 work under the names of the metals. The artificial compounds pro- 

 duced by the chemist, and the properties of the metals in relation to 

 one another, are treated of in the ARTS AND SCIENCES DIVISION of 

 this work. 



METAMORPHOSIS, a term employed in natural history to denote 

 those changes which plants and animals and their various organs 

 undergo in passing from their simpler and elementary conditions to 

 those which are more complex and compound. Thus the changes 

 which an insect undergoes in passing from its egg-state through its 

 caterpillar and chrysalis stages are called its metamorphoses. [INSECT.] 

 Another remarkable instance of changes of form to which this term 

 is applied is found in the Barnacles and Sea-Acorus. [CIRRIPEDIA.] 

 All animals exhibit these changes to a greater or less extent, and as 

 far as they have been observed in particular families or species they 

 are noticed in this work. [AMPHIBIA; CRUSTACEA; ACALEPH./E ; 

 MOLLUSCA; MARSUPIATA.] 



The general results of these changes as exhibited in the forms 

 which every species of plant or animal assumes at the period of its 

 highest development, are called the laws or science of Morphology. 

 [MORPHOLOGY.] 



The same general changes are observable in plants as in animals. 

 In plants however neither their organs nor conditions of existence are 

 so numerous and complicated as those of animals, and consequently 

 their metamorphoses are fewer. In animals each great group and 

 each system, as well as each organ, has its peculiar mode of develop- 

 ment and law of change, whilst in plants we find all parts resolvable 

 into the two great elements stem and leaves. Out of these two 

 fundamental organs all the modifications of bracts, stipules, sepals, 

 petals, stamens, fruit, and seed, are produced. 



Although the development of the organs of plants is now recognised 

 as a part of the history of the structure of each organ, this subject 

 has an interesting history, and has been frequently treated of as an 

 independent branch of botanical inquiry. The tracing back the 

 history of an organ to its elementary condition is of modern origin. 

 It seems first to have occurred to Linnscus, who in the second volume 

 of the tenth edition of the ' Systema Naturse," published in 1759, thus 

 expresses himself : " Leaves are the creation of the present year, 

 bracts of the second, calyx of the third, petals of the fourth, stamens 

 of the fifth, and the stamens are succeeded by the pistil. This is 

 apparent from Ornithogalums, luxuriant and proliferous plants, double 

 flowers, and Cardui." 



In December, 1760, these propositions were sustained by Linnseus 

 in a thesis called the 'Prolepsis Plantarum.' He commences by 

 remarking that " as soon aa leaves have expanded themselves in spring, 

 a bud is observable in the axil of each. This bud swells as the year 

 advances, and in time becomes manifestly composed of little scales : 

 in the autumn the leaves fall off, but the bud remains, and in the 

 succeeding spring swells, disengages itself from its envelopes, and 

 becomes lengthened : when its outer scales have dried up and fallen 

 off, the inner ones are expanded into leaves, which are separated by a 

 gradual extension of the young branch, and presently each new leaf 

 is found to contain in its bosom a little scaly bud, which in the follow- 

 ing season will also be developed aa a branch, with other leaves and 

 other buds. Now, when we see a tree adorned with leaves, and in 

 the bosom of these leaves provided with its little buds, we naturally 

 inquire of what do these buds consist ? Can it be of rudimentary 

 leaves, each with its budlets, the latter of other leaves and buds, and 

 so on to infinity, or at least as far as the extension of the plant is 

 likely to proceed ? Nature organises living beings out of such minute 

 particles, and even from fluids themselves, that the best eye may in 

 vain seek to penetrate far into her mysteries. I shall however endea- 

 vour to show that the composition of buds does not extend further 

 at one time than provision for six years ; just as, among animals, we 

 find the little Volvox globator containing within the mother its children, 

 grandchildren, great-grandchildren, and great-great-grandchildren 

 down to the sixth generation." 



The defects of this theory consisted, firstly, in its not accounting 

 for the modifications of the pistil; and, secondly, in the fanciful 

 supposition that the organs of fructification are prepared six years 

 beforehand, and that their peculiar appearance is owing to the time 

 of this development being anticipated by some unknown but ever- 

 acting cause. It was this which probably caused the whole theory to 

 be generally neglected. It was however maintained by Ludwig and 

 Wolff; the latter of whom in particular improved so much upon the 

 speculation of Linnseus, by rejecting what was fanciful and supplying 

 to a certain extent an explanation of the origin of the pistil, that 

 his paper in the ' Novi Commentarii Academies Petropolitana) ' for 



3F 



