76 



KNOWLEDGE. 



[Apbil 2, 1894. 



as to their probable mode of life and external appearance. 

 As regards the latter, it may be suggested that since both 

 sloths and anteaters are clothed with a thick covering of 

 coarse hair, it is highly probable that the same held good 

 in the case of their extinct relations. Further, from their 

 massive proportions, and also from their kinship to the 

 sloths, it is most likely that the ground-sloths were as slow 

 and deliberate in their movements as the latter. That 

 such monstrous creatures could not have existed in a tree- 

 less country like the Argentine pampas has been already 

 indicated in the first of the series of articles of which the 

 present is the conclusion, and we may hence assume that 

 in the days of the ground-sloths Argentina was much like 

 what Brazil is at the present day. Browsing on the leaves 

 and probably on the smaller branches of forest-trees, 

 the ground-sloths doubtless obtained their food by rearing 

 themselves up against the trunks, supported on the tripod 

 formed by then- massive hind limbs and powerful tail, the 

 ponderous structure of the pelvis being eminently adapted 

 for maintaining the body in such a posture. The same 

 massiveness of structure conclusively proves that the 

 creatures were not arboreal, since no tree capable of being 

 climbed could carry such an enormous weight. It was 

 suggested, mdeed, by Owen that the megathere was in the 

 habit, when reared up in the manner indicated above, of 

 clasping a tree in its arms and swaying it backwards and 

 forwards until it fell with a crash to the ground ; but 

 although such a radical mode of procedure may have been 

 occasionally resorted to, we have no right to assume that 

 such was the ordinary habit of the ground-sloths. 



THE MAKING OF DIAMONDS. 



By Vaughan Corkish, M.Sc, P.C.S. 



THE reproduction of the diamond by M. Moissan 

 has put the coping-stone to the work of miueral- 

 ogical synthesis. For some years past it has 

 been thought that the solution of this problem 

 was merely a matter of time and patience ; but it 

 is no little satisfaction to be able to say at last that the 

 thing has been done, for it is indeed a striking illustration 

 of the power over stubborn mattei; which is won by the 

 patient student of science. In the light of what has now 

 been accomplished, it may not be without interest to refer 

 to what was written in this journal on the subject of the 

 production of diamonds previously to the work of M. 

 Moissan. In Knowledge for May, 1891, at the conclusion 

 of an article on " The Artificial Production of Eubies," 

 the matter was referred to as follows :— 



" The great problem in the artificial production of gems 



is the preparation of the diamond In the case of 



other minerals the successful production has generally 

 only been achieved after a minute study of the mode of 

 natural occurrence, and this has afforded guidance as to 

 the best means of imitating the natural process of forma- 

 tion. It is only of recent years that the diamond has 

 been found in its original matrix, so that materials have 

 been wanting on which to base experimental methods. 

 The chemical nature of the body, a combustible substance, 

 is so different from that of the ruby and most other gems, 

 which are oxides or oxidized materials, that the methods 

 to be eruployed for its production will probably involve the 

 application of different principles. There is no reason, 

 however, to regard the problem as insoluble. When 

 sufficient guiding data have been obtained, skill will not 

 be wanting to imitate in the laboratory the conditions 

 under which Nature has worked in the formation of this 

 most beautiful product of the mineral world." 



What some of these determining conditions might be 

 was indicated in a subsequent paper on "The Diamond 

 Mines of South Africa," which appeared in Knowledge for 

 October, 1891. " To the mineralogist the chief interest 

 of the South African mines lies in the fact that the ' blue 

 rock ' or kimberlite appears to be the original matrix 



of the diamond It is worthy of note that 



a black shale forms one of the surrounding rocks, 

 and pieces of this shale have been found baked and other- 

 wise altered in the blue rock. The suggestion has been 

 thrown out that the diamonds were formed by the altera- 

 tion of the carbonaceous matter of the shale -under the 

 iyijiuenre of a moderately high temperature and great pressure. 

 Such indications are useful as affording suggestions to the 

 experimentalist, to whom in spite of previous failures we 

 must look to tell us definitely how the diamond is formed." 

 If the diamond be highly heated in the presence of 

 oxygen it takes fire, as is well known, and burns with the 

 formation of carbonic acid. If it be heated not in contact 

 with oxygen it swells up and blackens, reverting to the 

 ordinary charred form of carbon. But the action of heat 

 upon bodies is in many cases very different when they are 

 subjected to high pressure, a principle established by Sir 

 James Hall more than one hundred years ago in his cele- 

 brated research on the conversion of chalk into marble, 

 one of the achievements of experimental geology, described 

 in Knowledge for July, 1891. 



As will be seen, M. Moissan invoked the aid of pressure 

 to modify the action of heat in his experiments, and pro- 

 duced diamonds from charcoal, a substance of the same 

 nature as the "shale" which occurs in the Kimberley 

 rock. The foi-mation of crystals is, as a rule, best brought 

 about either by sublimation or by cooling a solution. 

 Carbon, however, cannot be distilled or sublimed, and is 

 insoluble in all ordinary solvents, such as water or aqueous 

 solutions of acids and alkalies, or in liquids such as alcohol, 

 ether or benzene. On the other hand, molten metals can 

 take up or dissolve carbon to a not inconsiderable extent, 

 as happens, for instance, in the well-known process of 

 iron-smelting. The molten iron in the blast furnace 

 dissolves some of the carbonaceous fuel, a part of which, 

 when the iron is allowed to cool and sohdify, crystallizes 

 out in plates of graphite. 



This is an example of the production of a crystalline 

 form of carbon from a non-crystalline variety, and it is at 

 the same time an instance of the artificial formation of a 

 mineral. 



M. Moissan, in his experiments, employed iron as a 

 solvent for carbon, which was in the form of charcoal ; 

 but he modified the action of heat and the solvent by 

 subjecting the carbon -saturated iron to considerable 

 pressure. It may be noted here that M. Moissan finds the 

 principal constituent in the ash of the native diamond to 

 be oxide of iron. It is known also that native diamonds 

 often contain liquefied gases in cavities of the crystal, and 

 that they are sometimes liable to spontaneous disruption, 

 owing to a state of strain which is probably due to their 

 having been formed under high pressure. 



In an earlier series of experiments, iron melted by 

 means of an electric furnace, and raised to a white heat, 

 was allowed to saturate itself with carbon in the form of 

 strongly compressed sugar charcoal. The crucible in 

 which the operation was conducted was then plunged into 

 cold water, which cools the outer portion of metal so as to 

 form an outer la_ver of solid iron. While this outer coating 

 is still red-hot the crucible is withdrawn from the water, 

 and the cooling proceeds more slowly. To realize what 

 goes on within the jacket of solid iron, we must remember 

 that the stiU hquid interior is molten iron, containing a 



