Volume 1

Watts' dictionary of chemistry / revised and entirely rewritten by H. Forster Morley and M.M. Pattison Muir ; assisted by eminent contributors.

  • Henry Watts
Date:
1888-1894
Catalogue details

Licence: Public Domain Mark

Credit: Watts' dictionary of chemistry / revised and entirely rewritten by H. Forster Morley and M.M. Pattison Muir ; assisted by eminent contributors. Source: Wellcome Collection.

    713/800 page 687
    Wood charcoal: -241 R. (l.c.). In 1874 Weber made careful determinations of the S.H. of the different forms of carbon at different temperatures; he used (1) diamond, (2) native graphite, (3) porous wood charcoal in a slender filament strongly heated in dry Cl and sealed at once in a glass tube. His chief results were as follows (v. P.M. [4] 49, 161 a. 276):— Diamond. Temp. -50° +10° 85° 250° 606° 985° S.H. -0635 -1128 -1765 -3026 -4408 -4529 Graphite. Temp. -50° +10° 61° 201° 250° 641° 978° S.H. -1138 -1604 T99 -2966 -325 -4454 -467 Wood Charcoal. Temp. 0° — 23° 0°-99° 0°-223° S.H. -1653 -1935 -2385 These numbers show that the S.H. increases as temp, increases, but that the rate of this in- crease is much smaller at high than at low temperatures. From 600° onwards the S.H. of diamond is the same as that of graphite; as the values for wood charcoal are nearly the same as those for graphite for the same temperature- intervals, the conclusions may fairly be drawn that at temperatures above 600° the different forms of carbon have all the same S.H., and that at lower temperatures there are two values for the S.H., one belonging to graphite and amor- phous C, the other to diamond. Allotropy of carbon. Carbon exhibits allotropic changes in a marked way ; diamond may be, superficially at any rate, changed to j graphite ; amorphous C may also be changed to ! graphite ; each of the three varieties is charac- terised by special properties. The S.G. of each is characteristic. The heats of combustion (v. supra) are different. The S.H.s are not the same; but Weber’s results tend to show that, as regards S.H., there is but one form of C ex- isting at temperatures above 600°. Amorphous C remained unchanged when subjected to a pressure of 6,000-7,000 atmos. (Spring, A. Ch. [5] 22, 170). The three forms are clearly dis- tinguished, chemically, by their reactions with KC103 and HNO? (v. Reactions, No. 9). A tomic weight.—Determined (1) by burn- ing diamond in O and weighing the CO. produced (Dumas a. Stas, A. Ch. [3] 1, 5; Erdmann a. Marchand, J. pr. 23, 159 ; Roscoe, A. Ch. [5] 26, 136; Friedel, Bl. (2] 41,100); (2) by heating silver acetate and weighing the Ag (Marignac, A. 59, 287); (3) by heating Ag salts (oxalate and acetate) and weighing the Ag and C02 formed (Maumen6, A. Ch. [3] 18, 41). The mean of all the (closely agreeing) results is ll-97 (0 = 15-96). Chemical properties.—The atom of C is tetravalent in gaseous molecules (CH„ CC1,„ CBrp Ac.). The atomicity of the molecule of C is unknown, as the element has not been gasi- fied ; certain considerations, e.g. the increase in S.H. as temperature increases, and perhaps the character of the spectrum, seem to indicate that the molecule of C is probably composed of several atoms. Carbon is distinctly a non-metallic element; it does not replace the H of acids to form salts; it forms stable, but easily gasified, compounds with the halogens; its oxides, and also the sulphide CS2, are distinctly acidic in their re- actions ; it exhibits allotropy in a most decided way; the spectrum of C is very complex; yet in some of the physical properties of graphite and dense amorphous carbon, this element approaches the metals (v. supra). Carbon stands at the beginning of Group IV. in the periodic classifica- tion of the elements ; the other members of this group, except Si, are more metallic than non- metallic ; C shows closer relations to Si, the first odd-series member of the group, than to any other element in the group (v. Carbon group op elements). Both elements are remarkable for the great number of compounds which they form with H, O, and N. Most of the elements of Group IV., except C, form characteristic com- pounds with F, or double compounds with F and other elements. Reactions.—1. Unchanged by action of acids. 2. Heat, in absence of air, produces no change (comp. Properties of Diamond). — 3. When strongly heated in excess of oxygen, CO., is formed: the combination is much retarded if the C and O are carefully dried (Baker, C. J. 47, 349).—4. Heated with sulphuric acid and potassium clichromate C is slowly burnt to C02. 5. Oxidised to C02 by heating with molten nitrate ox chlorate of potassium.—6. Reacts with sulphur vapour at high temperatures to form CS2.—7. Combines with hydrogen to form C2H2; by passing electric sparks between C poles in atmosphere of H.—8. Combines indirectly with nitrogen to form cyanogen.—9. Graphite is oxi- dised by potassium chlorate and nitric acid to graphitic acid (?C,,H405 or CnH,0(;). Brodie (T. 1859. 249) heated an intimate mixture of 1 part purified and very finely divided graphite and 3 parts KC103, with enough very cone. HN03Aq to bring all into solution, at 60° for 3-4 days, until yellow vapour ceased to come off; the contents of the retort were then poured into much water; the insoluble matter was tho- roughly washed by decantation, dried on a water-bath, and again oxidised by KC103 and HN03Aq, as before. These operations were repeated (usually 4 times) until no further change was produced, and the insoluble matter formed a clear-yellow solid. Analysis of this yellow solid, dried at 100°, gave the formula CnH,05. This body—called graphitic acid by Brodie — forms small, transparent, lustrous, yellow plates; it is slightly soluble in water; insoluble in water containing acids or salts; turns blue litmus slightly red; shaken with solutions of alkaline bases it appears to form insoluble salts, but the composition of these is very uncertain; when heated it burns explo- sively, leaving a fine, black residue; it is easily decomposed by reducing agents such as (NH,)HS, SnCl2, HIAq, Ac. (v. infra). Brodie supposed this body to be a compound of a hypothetical element which he called graphon, and to which lie gave the atomic weight 33; he formulated graphitic acid as Gr.,H.|05, and regarded it as the carbon analogue of a silicic acid Si,H,03 obtained by Wohler from graphitoidal silicon. Gottsclialk (J.pr. 96,321) placed a very intimate mixture of 1 part (50grms.) purified, very finely divided graphite with 3 parts KC10a in a large flask surrounded by ice-cold water, and very
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