April" 2, 1894.] 



KNOWLEDGE. 



77 



large excess of dissolved carbon, and that iron expands in 

 the process of solidifying. Hence, during the process of 

 solidification within the jacket or crust of chilled metal, 

 great pressure is exerted. The process of solidification, 

 therefore, goes on slowly and under great pressure, and 

 examination of the resulting product showed that, under 

 these changed conditions a part only of the surplus 

 carbon had crystallized out as graphite, and that in the 

 residue left after dissolving away all the iron by means of 

 boiUng hydrochloric acid and other solvents there was a cer- 

 tain quantity of a denser form of carbon (having a specific 

 gravity of 3 to 3'5), and hard enough to scratch a ruby ; 

 and that among these heavier portions of the residue were 

 transparent particles, having a greasy or waxy lustre, and 

 marked with parallel strise and triangular depressions. 

 These transparent particles burnt when heated to 1050° C. 

 in oxygen gas, and as it appeared, with the formation of 

 carbonic acid ; but the particles were too small to allow of a 

 quantitative experiment. Similar results were obtained by 

 the slightly modified method of rapidly cooling an ingot of 

 molten iron saturated with carbon from a temperature 

 of 2000° C. In a few cases small fragments were obtained 

 " qu'ils resseniblent anx petites fragments dc diamant trans- 

 parents que nous avons rencontres dans la ' terre bleu' du Cap" 

 (Comptes rend/us, February 6th, 1894). The result may be 

 summed up by saying that, up to the date of the experiments 

 described in the above quoted paper, M. Moissan appears 

 to have succeeded in reproducimj that transparent variety of 

 carbon of which native diamonds are composed. The 

 specimens could hardly be called diamonds, although they 

 showed certain characters of the native diamond — e.g., a 

 waxy lustre, and parallel strife and triangular depressions 

 on the surface. 



Since the experiments above described, a happy modifi- 

 cation of the method employed has given results of a far 

 superior kind, perfect diamonds being formed, having the 

 distinctive physical peculiarities of the native stone, and of 

 sufficient size for M. Moissan to prove by quantitative 

 chemical experiments upon some of the specimens that 

 they burnt with the formation of pure carbonic acid. In 

 the course of experiments made in former years by other 

 experimenters using other methods, transparent crystalline 

 bodies were obtained which were thought to be diamonds, 

 until their failure to satisfy the carbonic acid test showed 

 that the crystalline particles were not composed of carbon. 



Moissan's modified method is as follows : — Iron is 

 saturated with carbon at the white heat of an electric 

 furnace, and under pressure. The crucible containing the 

 molten iron is then quickly lowered to the bottom of a bath 

 of melted lead. This ensures quicker cooling than when the 

 iron is plunged in water, owing to the fact, first, that the 

 white-hot iron does not really come into contact with the 

 water, and secondly, that the lead is a good conductor and 

 carries away the heat rapidly. It seems that the two 

 liquid metals behave towards one another much as oil and 

 water, and the molten iron collects in spherical globules 

 which rise to the surface of the molten lead, the difierence in 

 the specific gravity of molten iron and of molten lead being 

 of course very considerable. The surface of the drops of 

 liquid iron which float upon the surface of the lead quickly 

 solidifies, the smaller drops with a diameter of one to two 

 centimetres first, the larger drops after a lapse of a longer 

 time, and the solid little balls of iron are left to float on 

 the molten lead where they cool down. The interior of 

 the balls is of course liquid long after the formation of 

 the solid crust. The tendency of the central parts to 

 solidify is resisted by the solid crust, owing to the fact 

 before mentioned, that iron expands in the act of solidifi- 

 cation. Meanwhile a part of the carbon crystallizes out 



from its solution in the liquid iron. After a time, aa the 

 cooling goes on, the lead also solidifies, and the little iron 

 balls are left imbedded in the ingot of lead. Then begins 

 the process of getting at the small quantity of the car- 

 bonaceous material which it is desired to examine. The 

 lead which adheres to the iron is dissolved away with 

 nitric acid, the iron itself is dissolved by hydrochloric acid, 

 and further treatment with suitable solvents leaves the 

 sought-for residue, a small quantity of material left after 

 the tedious process of removing by slow chemical means 

 the relatively large mass of metal. 



Transparent diamonds are found in the residue having 

 well-defined crystalline faces, striated and marked in the 

 well-known way, and the edges generally curved ; they 

 have the high refracting power, the specific gravity, and 

 the hardness of the native stone. The peculiar form known 

 as the hemiliedral predominates amongst these crystals aa 

 in those of native diamonds, and their formation under 

 pressure is found to give rise to the phenomena of anoma- 

 lous polarization of the light which passes through them, 

 as well as occasionally to spontaneous disruption ; charac- 

 ters which, as has been mentioned, are sometimes noticed 

 in the native stone. The diamonds are of course small ; 

 one with a diameter of half a millimetre appears to be 

 reckoned a fine specimen. Further practice in working 

 the process will probably enable larger specimens to be 

 obtained, as has been the case with the production of 

 rubies, which are now produced of a size sufficient to be 

 used in the jewelling of watches. 



However this may be, the production of diamond ia 

 now an accomplished fact, achieved by the patient skill 

 of the same worker who, seven years ago, successfully 

 overcame the great experimental difficulties which had 

 rendered fruitless the many former attempts to isolate the 

 chemical element fluorine. 



STINGING INSECTS. -III. 



By E. A. Butler. 

 (Continued from page 56.) 



ALL the stinging insects hitherto described have 

 carried their weapons at their tail, where they 

 form an instrument more or less closely connected 

 with the process of egg-laying. Our third group 

 of so-called stingers, for in this case the epithet 

 is hardly accurate, comprises those that make punctures 

 with their mouth organs, and often cause much pain and 

 inflammation by so doing. The insects, in fact, feed on 

 animal juices, and the " stings " are the necessary results 

 of their attempts to obtain food, and do not form incidents 

 in a hostile demonstration. All the members of this group 

 belong to two orders — the Diptera, or flies, and the 

 Hemiptera, or bugs. Taking the former first, we may 

 remind our readers that we have on former occasions, in 

 the articles on various household pests, discussed at some 

 length the so-called "bites" or stings of some of the 

 greatest sinners in this direction, viz., gnats, mosquitos, 

 fleas, and the stinging house-fly (Stomoxys), and these 

 details need not be repeated here. But there are a few 

 other flies that are often very troublesome in the same way, 

 though they do not enter our houses, but only pimish us 

 when we invade their domains in woods or marshes. One 

 of the most noted of these has such a blood-thirsty appetite 

 that it has been named Hamatopota, i.e., blood-drinker. 

 It is an inhabitant of damp spots in woods, and though 

 plentiful enough, is hardly likely to be noticed till painful 

 experience in the shape of a sharp and sudden prick on 

 hand or neck awakens us to consciousness of its presence. 



