CARBON. 



CARBON. 



610 



GRAPHITE [NAT. HIST. Div.], whilst the amorphous kiud is met with 

 as mineral charcoal interspersed amongst coal and anthracite. 



The second group, the carbonates, presents us with a numerous 

 mineralogical family of the highest interest, both in a scientific and in 

 an economical point of view. For the purpose of studying them with 

 the greatest facility the carbonate of lime may be taken as a type, to 

 which the whole family may be conveniently referred. This substance 

 possesses the peculiarity of dimorphism ; that is to say, it occurs in 

 forma belonging to two different systems of crystallisation, namely, 

 the rhombohedral and the prismatic, and is called, when its crystals 

 belong to the former, CALCAREOUS SPAR, and when to the latter 

 ARRAGOXITE, under which terms they are described in NAT. HIST. Dry. 

 The chemical composition of these minerals is that of a neutral salt, 

 being one atom of carbonic acid united with one atom of the oxide of 

 calcium, or lime, and therefore the chemical composition of both is 

 denoted by the symbol CaO C0. 2 . But the oxide of calcium is isomor- 

 phous with the similarly constituted oxides of magnesium, barium, 

 strontium, iron, manganese, zinc, cerium, lead, and copper ; and each 

 of these oxides occurs combined with carbonic acid in the proportion 

 of atom to atom, some of them producing crystals isomorphous with 

 culc-spar, and others on the contrary with arragonite. But in addition 

 to the mineral species produced by the combination of any one of 

 these oxides with carbonic acid, an endless variety of isomorphous 

 crystals is formed by the combination of two or more of the above 

 carbonates, which are capable, according to the laws of isomorphism, of 

 uniting in any proportion, as may be seen in the varieties of calc-spar, 

 which are known as brown-spar, bitter-spar, dolomite, where portions 

 > if the oxide of calcium are constantly replaced by the oxides of 

 magnesium, iron, and manganese. None of the carbonates of these 

 oxides are found, however, like the carbonate of lime, to be dimor- 

 phous, and to occur crystallised both in the rhombohedral and the 

 prismatic system ; they may be divided therefore into two isomorphous 

 groups, the one headed by calc-spar, and the other by arragonite ; and it 

 is only among the oxides of the same group that it is usual to find the 

 one oxide substituted for the other. 



The first group crystallised in the rhombohedral system consists of 



Calc-spar . 

 Magnesite or talc-spar 

 Manganese-spur 

 Iron-spar . 

 Zinc-spar . . 

 Bitter-spar 

 Brown-spar . . 



CaO CO, 



MgO CO, 



MnO CO., 



FcO CO, 



ZnO CO, 



CaO CO, + MgO CO 3 



(CaO, SIgO, MnO, FeO) CO, 



The second group crystallised in the prismatic system consists of 



Arragonite 

 Strontianitc 

 Witherite . 

 White Lead 



CaO CO.. 

 SrO CO, 

 BaO CO 3 

 PbO CO. 



But although the minerals of these groups are classified together 

 as being isomorphous, this word cannot be used in its strictest sense, 

 and -as denoting an exact identity of the angles of inclination between 

 corresponding planes in the different species, as those when measured 

 at the ordinary temperature are found to differ from each other by 

 small but nevertheless very perceptible magnitudes. The following 

 table of the angles in the terminal edges of the ground-forms of the 

 principal species of the first group, and parallel to the faces of which 

 the cleavage planes of each occur, will best show this difference. 

 According to the most careful measurements the angles are : 



For Calc-spar 105 5' 



Bitter-spar 

 , Manganese-spar 

 , Iron-spar 

 , Talc-spar 



Zinc-spar 



106 15 



106 51 



107 

 107 25 

 107 40 



The three angles of calc-spar, bitter-spr, and talc-spar, when the 

 chemical composition of these minerals is considered, present a very 

 interesting and striking relation, the angle of bitter-spar being the 

 aritkmetical mean between those of the pure carbonates of lime and 

 magnesia, while its chemical composition may be considered also as 

 the mean of the other two, being composed of an atom of carbonate of 

 lime united with an atom of carbonate of magnesia. That this is a 

 particular instance of a more general law, that the increment of the 

 angle in any compound over that of calc-spar is to the whole difference 

 of the angles of the pure minerals, or 2 20', in the proportion of the 

 number of atoms of carbonate of magnesia to the total number of 

 atoms in the compound, appears to be established by the analysis and 

 measurements of the French mineralogist, M. Beudant, who has made 

 several experiments for the purpose of ascertaining this fact. An 

 example will at once render this clear. Suppose on measuring the 

 angle of a coni]xnmd of carbonate of lime and magnesia we find it to 

 be 105 W, which gives an increase over 105 5' equal to J of 2 20'; 

 according to the experiment* of Beudant we should be justified in 

 concluding that the compound consisted of three atoms of carbonate 

 of lime to oue of carbonate of magnesia. 



ARTH AXD SCT. DIV. VOT,. II. 



In addition to the carbonates above mentioned, four others are 

 known, namely, the native soda, Gay-Luasite, 1'azure or blue copper, 

 and malachite, which, although containing elements isomorphous 

 with the former, are nevertheless differently crystallised, as they 

 are of a different chemical composition, containing water of crystal- 

 lisation. 



The third class, all of which contain more or less evidence of their 

 vegetable origin, are amorphous. They are all distinguished from 

 other mineral bodies by their combustibility, the combustion being 

 usually accompanied by flame. They may be divided into the four 

 principal groups of coals, mineral resins, mineral oils, mineral pitches 

 or bituminous bodies. The principal varieties are distinguished by 

 and are described under the names of peat ; coal and its varieties, brown 

 coal, &c. ; amber, honeystone, resinasphaltum, naphtha, petroleum, 

 mineral pitch, asphaltum. 



CARBON (C), a non-metallic elementary solid body, which is widely 

 diffused throughout nature. The purest, and at the same time the 

 rarest form in which it occurs is that of the diamond [DIAMOND, in 

 NAT. HIST. Div.] ; the more common states in which it is met with 

 are those of graphite [GRAPHITE, in NAT. HIST. Div.] and mineral 

 charcoal ; but in these cases it is not free from admixture. 



Another well-known form of carbon, but still impure, is the charcoal 

 obtained from the decomposition of wood by heat. 



The diamond differs so entirely in its obvious and physical proper- 

 ties from carbon in its more common states, that nothing less than the 

 most decisive evidence of the identity of their chemical nature could 

 have allowed of their being arranged together : the proof of their 

 .similarity is stated in the article CARBONIC ACID. In addition to 

 these forms in which carbon occurs pure or in a free state, it is also 

 met with in combination with other elements, in fact by far the largest 

 amount of carbon is thus met with in combination. In combination 

 with oxygen as carbonic acid, it occurs in the atmosphere, and dissolves 

 in the waters of the ocean, rivers, springs, &c. In the same form, but 

 further combined with lime and magnesia, it exists in enormous 

 quantity in the earth's strata, as limestone, chalk, marble, dolomite, &c. ; 

 whilst combined chiefly with hydrogen, oxygen, and nitrogen, it enters 

 largely into the composition of coal, peat, and lignite, as also of all 

 animal and vegetable substances. From, its invariable presence in 

 organic substances it has been named the organic element. 



Charcoal has already been mentioned as carbon procured from the 

 decomposition of wood by burning. This operation is generally con- 

 ducted in pits made in the ground ; sometimes however it is carried on 

 in iron cylinders. Wood is essentially composed of carbon, oxygen, and 

 hydrogen ; by the action of the heat it is decomposed, the oxygen and 

 hydrogen are expelled, and uniting in certain proportions form water, 

 and also with carbon various gaseous and other compounds are formed. 

 Among the latter are acetic acid, sometimes called pyroligneous acid, 

 and a peculiar inflammable fluid, known by the name of pyroxilic 

 spirit, and tar. 



The remaining charcoal has the following properties : it is black, 

 lighter than water, and full of pores, occasioned by the expulsion of the 

 bodies volatilised. The heavier the wood from which the charcoal is 

 obtained, the denser it is. 



Charcoal, from whatever source procured, is absolutely infusible by 

 any degree of heat however great ; neither that of a mirror, the oxy- 

 hydrogeu blow-pipe, nor the voltaic discharge, being sufficient to 

 produce fusion. In its common state it is one of the worst conductors 

 of heat known, but its power is increased after being strongly heated. 

 Charcoal is a conductor of electricity, which is so far from being the 

 case with the diamond, that it may without insulation be rendered 

 electrical by friction. 



Charcoal is tasteless, inodorous, and insoluble in water. It pos- 

 sesses the property of destroying colouring matter, especially the 

 charcoal procured by burning bones, which is usually called animal 

 charcoal ; it is largely used for this purpose in sugar-refining. [BoNE 

 BLACK.] 



Charcoal, in common with other porous bodies, has the power of 

 condensing gaseous bodies ; but to a greater degree than most, or 

 perhaps any other substances : graphite, on account of its compactness, 

 does not possess this quality. 



Saussure performed experiments to ascertain these facts by plunging 

 a piece of red-hot charcoal under mercury, and introducing it when 

 cool into the gas. He found that box-wood charcoal absorbed in 24 to 

 36 hours the annexed quantities of the following gases : 



Hydrogen . . . 



Nitrogen 



Oxygen 



Carbonic oxide . 



Olefiant gas 



Carbonic acid 



Nitrous oxide 



Sulphuretted hydrogen 



Sulphurous acid 



Hydrochloric acid . 



Ammoniacal gas 



. 1'75 times its volume. 



. 7'5 



. 9-25 



. 9-42 



. 35- 



. 35- 



. 40' 



. 55- 



65- 



. 85- 



. 90- 



These effects appear to depend entirely upon the mechanical action 



u it 



