508 Sir W. Roberts-Austen [Feb. 22, 



mium. Ferro-titanium, with 20 to 25 per cent, of titanium, and alloys 

 of titanium and manganese containing from 30 to 35 per cent, of tita- 

 nium, have also been produced. Titanium, moreover, absorbs nitrogen, 

 and ferro-titanium is found to be very useful in producing sound steel 

 castings. I, quite independently of Dr. Goldschmidt, succeeded in the 

 preparation of alloys of iron with from 3 to 25 per cent, of boron, the 

 alloy containing 3 per cent, of boron proving to be beautifully crys- 

 tallised. Dr. Goldschmidt states that definite results have not been 

 obtained in attempts to utilise it. I am still investigating this most 

 interesting subject. Dr. Goldschmidt has obtained ferro-vanadium, 

 the best results being obtained with steel containing 0'5 per cent, of 

 vanadium. He has also prepared an alloy of lead and barium con- 

 taining 30 per cent, of barium, which affords an example of the pos- 

 sibility of forming alloys of metals with those of the alkaline earths 

 by this process. 



It only remains for me to direct your attention to the nature of the 

 solid product of the combustion of aluminium, which is alumina often 

 of a high degree of purity, and in a specially interesting form. The 

 alumina from the reduction of oxide of chromium, when it is allowed 

 to cool, forms large ruby-tinted crystalline masses, closely resembling 

 the natural ruby. I have now to show you on the screen some rubies 

 and sapphires produced as an incident of this beautiful process. The 

 blue sapphire mass is, however, only translucent, not transparent. 

 The ruby crystals are often very beautiful, as these slides show. 

 Rubies placed in a vacuum tube and subjected to the bombardment of 

 an electric discharge are, as Sir William Crookes has taught us, 

 beautifully phosphorescent. I have here in this tube some thin crys- 

 talline plates of artificial ruby ; they become beautifully phosphores- 

 cent when the current from the induction coil is passed through the 

 tube, and by the kindness of Sir William Crookes I can show you 

 some true rubies treated in a similar way. The behaviour of the arti- 

 ficial rubies in the vacuum tube is not quite as brilliant as that of the 

 natural ones, but hitherto no special attention has been devoted to their 

 preparation ; they are simply thin plates broken from a large crystal- 

 line mass of slag such as that on the table. I may add that this 

 variety of corundum produced by the burning of aluminium is very 

 hard, and may be used, not only for the same purposes as ordinary 

 corundum, but for lining the crucibles in which the operations are con- 

 ducted, so that the product of combustion takes its place in conduct- 

 ing the process. My warmest thanks are due to Dr. Goldschmidt for 

 lending me the beautiful specimens on the table, and to Mr. W. H. 

 Merrett for his aid in conducting the experiments. 



I have set before you the considerations respecting the use of 

 metals as fuel simply as they appear to flow. I trust that the adoption 

 of the title of this lecture has been justified by the evidence given as 

 to the possibility of using metals as fuel in the strictest sense of the 

 word. It is well to be accurate on this point, because we are told that 

 the first known appearance of the word " fuel " in the English Ian- 



