518 Professor W. Chandler Roberts- Austen [March 15, 



Hitherto I have appealed to industrial work, rather than to 

 abstract science, for illustrations of the services which the rarer 

 metals may render. One reason for this is that at present we have 

 but little knowledge of some of the rarer metals apart from their 

 association with carbon. The metals yielded by treatment of oxides 

 in the electric arc are always carburised. There are, in fact, some of 

 the rarer metals which we, as yet, can hardly be said to know except as 

 carbides. As the following experiment is the last of the series, I 

 would express my thanks to my assistant, Mr. Stansfield, for the great 

 care he has bestowed in order to ensure their success. Here is the 

 carbide of calcium which is produced by heating lime and carbon in 

 the electric arc. It possesses great chemical activity, for if it is 

 placed in water the calcium seizes the oxygen of the water, while the 

 carbon also combines with the hydrogen, and acetylene is the result, 

 which burns brilliantly. [Experiment shown.] If the carbide of 

 calcium be placed in chlorine water, evil-smelling chloride of carbon 

 is formed. 



In studying the relations of the rarer metals to iron, it is 

 impossible to dissociate them from the influence exerted by the 

 simultaneous presence of carbon ; but carbon is a protean element — 

 it may be dissolved in iron, or it may exist in iron in any of the varied 

 forms in which we know it when it is free. Matthiessen, the great 

 authority on alloys, actually writes of tie " carbon-iron alloys." I do 

 not hesitate, therefore, on the ground that the subject might appear to 

 be without the limits of the title of this lecture, to point to one other 

 result which has been achieved by M. Moissan. Here is a fragment 

 of pig iron highly carburised ; melt it in the electric arc in the presence 

 of carbon, and cool the molten metal suddenly, preferably by plunging 

 it into molten lead. Cast iron expands on solidification, and the little 

 mass will become solid at its surface and will contract ; but when, in 

 turn, the still fluid mass in the interior cools, it expands against the 

 solid crust, and consequently solidifies under great pressure. Dissolve 

 such a mass of carburised iron in nitric acid to which chlorate of potash 

 is added ; treat the residue with caustic potash, submit it to the pro- 

 longed attack of hydrofluoric acid, then to boiling sulphuric acid, and 

 finally fuse it with potash, to remove any traces of carbide of silicon, 

 and you have carbon left, but — in the form of diamonds. 



If you will not expect to see too much, I will show you some 

 diamonds I have prepared by strictly following the directions of 

 M. Moissan. As he points out, these diamonds, being produced under 

 stress, are not entirely without action on polarised light, and they 

 have, sometimes, the singular property of flying to pieces like 

 Rupert's drops when they are mounted as preparations for the micro- 

 scope. [The images of many small specimens were projected on the 

 screen from the microscope, and Fig. 10, E, shows a sketch of one of 

 these. The largest diamond yet produced by M. Moissan is 0'5 

 millimetre in diameter.] 



A (Fig. 10) represents the rounded, pitted surface of a diamond, 



