56o 



NA TURE 



[August S, 1901 



METALS AS FUEL} 

 A CAREFUL metallurgist,- writing in the eighteenth century, 

 ■^^ claimed that " every matter which is combustible either 

 wholly or in part, is called fuel, the pabulum of fire." The word 

 is, however, usually restricted to substances which may be burnt 

 by means of atmospheric air with sufficient rapidity to evolve 

 heat capable of being applied to economic purposes. The latter 

 definition covers certain metals, though it was doubtless framed 

 to include only carbon and associations of carbon and hydrogen, 

 such as coal. The omission from the definition of the reference 

 to atmospheric air would enable the list of metals which might 

 be used as fuel to be widely extended. 



It has long been known that metals will burn, and it would 

 be easy to show that the history of inorganic chemistry is 

 epitomised and enshrined in a mass of litharge, which is simply 

 burnt lead. Successive generations of chemists, from Geber 

 in the eighth century to Lavoisier in the eighteenth, studied 

 litharge carefully before the latter proved partly by its aid 

 the identity of respiration, calcination and combustion. Into 

 this history I need not enter, but it may be pointed out that 

 Sir Isaac Newton^ had a clear idea as to the possibility of 

 burning metals. " Is not fire," he asks, " a body heated so hot 

 as to emit light copiously?" ..." for what else is red hot 

 iron than fire ? " and he significantly adds, " metals in fusion do 

 not flame for want of copious fume." He was, moreover, 

 aware that a mixture of lead and tin " suitably heated " does 

 emit "fume and flame," and, in fact, a mass of i part tin and 

 4 parts lead, which looks metallic, will, if it is kindled, continue 

 to burn like an inferior variety of peat, leaving an ash-like 

 product which may be used as an enamel. 



I propose to show that metals may be burnt for the sake of 

 the heat and light they produce, just as ordinary fuels are burnt," 

 except that in burning ordinary fuels combustion is often effected 

 in two distinct steps or stages, in the first of which carbonic 

 oxide is formed, and in the second carbonic acid, the products 

 in both cases being gaseous. When metals are burnt, the pro- 

 ducts of combustion are solid, or condense to solids, and they 

 therefore present a marked contrast to ordinary fuels which, as 

 has just been stated, yield on combustion gaseous products. As 

 I shall have but little to say about the light which attends the 

 combustion of metals, I may as well dismiss the subject by refer- 

 ence to a familiar application of the burning of metals for the 

 purpo.se of illumination. It is easy to fire electrically a portion 

 of what is known as a " magnesium star," and a ' ' fire-ball " of 

 magnesium attached to a parachute is beautifully packed in this 

 shell, for the loan of which I am indebted to the authorities of 

 the Royal Arsenal, Woolwich, and when the shell explodes the 

 stars burn and illuminate the enemy's position in the darkness 

 of night, so that guns may be laid to place projectiles in the 

 enemy's lines. 



Before proceeding further, I want to use the electric furnace as 

 affording a basis of comparison with the method of producing 

 high temperatures by the combustion of metals, which I shall 

 proceed to show subsequently. A current of loo amperes at 

 200 volts is passed by carbon poles into the furnace in which 

 pig iron is being melted ; directly the last piece of iron has 

 become fluid, the temperature of the fused pool must be about 

 1300° C. The fluid mass is reflected on the screen merely to 

 give some indication as to the appearance of such a mass at 

 1 300 ' C. , and not to afford a test of the capabilities of the electric 

 furnace. Later on I hope to show that a far higher temperature 

 can be produced by very simple means in a receptacle of about 

 the same capacity as the laboratory part of the furnace. 



Henceforth in the course of this lecture metals will be burnt 

 for the sake of the heat which is the result of their combustion. 

 From this point of view metallurgists have long used metals as 

 fuel, often without due recognition of the fact, but case after case 

 could be cited in which conducting definite metallurgical opera- 

 tions is made possible by burning portions of the metal or metals 

 under treatment. Time will perhaps be saved if I place in sharp 

 contrast the use of ordinary fuel and metallic fuel, even though 

 it takes us rather far back, for I do not want it to be thought 



1 A Friday Evening Discourse delivered on February 22, igoi, at 

 the R0y.1l Institution, by Sir W. Roberts-Austen, K.C.B., F.R.S. The 

 lecture consisted mainly of a series of experiments conducted at ver>- high 

 difficult to give a continuous 



temperat 

 abstract 01 it. 

 "- C. E. Gellert, 



and apart from then 

 Metallurgic Che 



that the use of metals as fuel is new, although their adoption for 

 this purpose has recently been greatly stim.ulated. Here is a 

 mass of very ordinary iron ore picked up on a heath in Surrey, 

 which skirts the site of what was once the ancient forest of 

 Anderida. The pre-historic dweller on the heath who used the 

 beautiful flint arrowheads, which are found near the iron ore, 

 merely burnt the wood of the forest to warm himself or to cook 

 his food. But the Britons whom C-esar found in Andreaswold 

 smelted iron with the wood of the forest trees, from which they 

 prepared charcoal, and smelting iron was actively conducted in 

 Queen EHzabeth's reign, and even survived into the last century 

 in the district I am contemplating. But in smelting iron, carbon 

 became associated with it and played a subtle part, rendering 

 the iron precious for certain purposes and useless for others. 

 Iron had therefore to be " decarburised " with a view to its con- 

 version into steel, and in doing this metallurgists for centuries 

 truly burnt some of the iron itself, using it actually as fuel. I 

 will only add that the use of metals as fuel assumed magnificent 

 proportions in the hands of Bessemer, as may be illustrated by 

 an experiment. A few pounds of a compound of iron, carbon, 

 silicon and manganese is melted in the wind furnace, simply 

 used because it affords a convenient method of melting the mass, 

 which is turned into a small Bessemer converter. A stream of 

 oxygen is directed into the fluid mass. Air would do, but with 

 so small a mass the free nitrogen would cool it too rapidly. In a 

 few seconds the carbon in the fluid will be burnt away, neverthe- 

 less the mass gradually becomes hotter and hotter, notwithstand- 

 ing the loss of carbon. A brilliant pyrotechnic display is the result. 

 The metalloid silicon is now burning, and then brown fumes of 

 iron and manganese pass freely off ; these metals are truly burn- 

 ing and are maintaining the heat of the bath, and the presence 

 of their fumes shows that it is time to stop the operation. The 

 temperature is somewhere near 2000° C, but according to some 

 recent investigations of Prof. Noel Hartley (Pliil. Trans., 

 vol. cxcvi. series A, p. 479, 1901), a temperature of more than 

 2000" C. is attained in the converter. Bessemer gave the world 

 in 1856 cheap steel ; we therefore owe to him the inestimable 

 benefits that are the results of that gift, and I ask you to bear in 

 mind that his great service to the industry of which we as a 

 nation are so justly proud rested on the possibility of using 

 metalloids and metals as fuel. I have already promised that in 

 the course of the lecture I will show some experiments in which 

 the temperature will be a thousand degrees higher than in the 

 one you have just seen. In the Bessemer process the products 

 of combustion are both gaseous and solid, and in a very ordinary 

 case the heat engendered by the carbon of the bath which 

 evolves gases is only half that which results from the combustion 

 of the silicon, iron and mang.anese which yield solid products. 

 As regards the " open-hearth process," in the phase of it which 

 is knosvn as the " pig and ore " process, oxygen is presented 

 and heat is produced under similar conditions to those we shall 

 consider subsequently in the case of the action of aluminium on 

 ferric oxide. 



3 " Optic." pp. 316-319, quoted by Shav 

 Boyle, vol. ii. p. 400. 



NO. 1658, VOL. 64] 



istry," trans, by I. S. (London, 1776), 

 s edition of the works of 



This table, which contains the relative calorific powers of 

 different metals and metalloids as compared with carbon, indi- 

 cates the advantage which certain metals possess over carbon 

 for use as fuel. 'The question at once presents itself, at what 

 temperature will such metals as can be used for fuel begin to 

 abstract oxygen from the air ? The answer is, it depends on 



