514 



NATURE 



\SepL 19, 1889 



■even the solid state, jii?t a=; we find the vapour of water dififused 

 through our present atmosphere does now. That which is true 

 of changes of physical condition, Henri Ste. Claire Deville, in 

 his brilliant theory of dissociation, has shown to be equally true 

 with respect to chemical changes ; and the cooling of the vapours 

 forming the earth wliile in its gaseous condition was necessarily 

 accompanied by chemical combinations, which took place 

 chiefly on -the outer surface, where oxides of the metals were 

 formed ; and as these are generally less volatile than the metals 

 themselves, they were precipitated on to what there then was of 

 liquid or solid of the earth, in the form of metallic rain or snow, 

 and were again probably decomposed, in part at least, to their 

 vaporous condition. The necessary consequence of this action 

 is that the inner regions of the earth must consist of substances 

 the vapours of which have high specific densities and high mole- 

 cular weights — that is to say, composed of elements having high 

 atomic weights — and that the heavier elementary substances 

 would collect nearer the centre, while the lighter ones would be 

 found nearer the surface. Our knowledge of the earth's crust 

 extends but to an insignificant distance ; yet, as far as we do 

 know it, we find that the arrangement above indicated prevails. 

 Hydrogen, carbon, nitrogen, oxygen, sodium, magnesium, 

 aluminium, silicon, phosphoru'^, sulphur, chlorine, potassium, 

 ■calcium — substances whose atomic weights range from i to 40 — 

 became condensed, entered into every conceivable combination 

 with each other, and produced substances the specific gravity of 

 which averages about 2i, never exceeds 4, and are found near 

 the immediate surface of the globe. 



But the mean specific gravity of the earth, as determined by 

 Maskelyne, Cavendish, and others, certainly exceeds 5, and 

 consequently the inner portion of our globe must be composed 

 ■of substances heavier than those existing on the surface, and 

 such substances are only to be found among the elements with 

 high atomic weights. The question arises. What elements of 

 this character are we likely to find in the depths of the earth? 

 In the first place, since gases diffuse through each other, a 

 certain proportion of the elements of high atomic weiijht will also 

 be found on the surface of the earth. Secondly, the elements 

 forming the bulk of the earth must be found in the atmo- 

 sphere of the sun — if, indeed, the earth once formed part of its 

 atmosphere ; and of all the elements, iron, with a specific 

 gravity exceeding 7, and with an atomic weight of 56, corre- 

 sponds best with these requirements, for it is found in abundance 

 on the surface of the earth ; and the spectroscope has revealed 

 the very marked presence of iron in the sun, where it must be 

 partly in the fluid and partly in the gaseous state ; and con- 

 sequently iron in large masses must exist in the earth ; so that 

 the mean specific gravity of our planet may well be 5, the value 

 which has been determined by independent means. 



It is not easy, however, to define in what condition the mass 

 of iron which must exist in the heart of the earth is likely to be. 

 Iron is capable of forming a vast number of combinations, de- 

 pending upon the relative proportion of the various elements 

 present. Thus, in the blast-furnace, oxygen, carbon, nitrogen, 

 calcium, silicon, and iron are associated, and produce, under the 

 action of heat, besides various gases, a carburet of iron and slag, 

 the latter containing chiefly silicon, calcium, and oxygen — that is 

 to say, substances similar to those which form the bulk of the 

 surface cf the earth. But these same elements, if there be an 

 excess of oxygen, will not yield any carburet of iron ; and the 

 same result will follow if there be a deficiency of silicon and 

 calcium, because of the large proportion of oxygen which they 

 appropriate. In the same way, during the cooling of the earth, 

 if oxygen, carbon, and iron were associated, and if the carbon 

 were in excess of the oxygen, the greater part of the carbon 

 would escape in the gaseous state, while the remaining part would 

 unite with the iron. It is certain that, in the heart of the earth, 

 there must have been a deficiency of oxygen, because of its low 

 specific gravity ; and the argument is supported by the fact that 

 free oxygen and its compounds with the lighter elements 

 abound on the surface. Further, it must be presumed that much 

 of the iron existing at great depths must be covered over and 

 protected from oxygen by a coating of slag ; so that, taking all 

 these considerations into account, it is reasonable to conclude 

 that deep down in the earth there exist large masses of iron in 

 part at least in the metallic state or combined with carbon. 



The above views receive considerable confirmation from the 

 composition of meteoric matter, for it also forms a portion of 

 the solar system, and originated, like the earth, from out of the 

 solar atmosphere. Meteorites are most probably fragments of 



planets, and a large proportion of them include iron in their 

 composition, often as carbides, in the same form as ordinary 

 cast-iron — that is to say, a part of the carbon is free and a part 

 is in chemical union with the iron. It has been shown, besides, 

 that all basalts contain iron, and basalts are nothing more than 

 lavas forced by volcanic eruptions from the heart of the earth to 

 its surface. The same causes may have led to the existence of 

 combinations of carbon with other metals. 



The process of the formation of petroleum seems to be the 

 following : — It is generally admitted that the crust of the earth is 

 very thin in comparison with the diameter of the latter, and 

 that this crust incloses soft or fluid substances, among which the 

 carbides of iron and of other metals find a place. When, in 

 consequence of cooling or some other cause, a fissure takes place 

 through which a mountain range is protruded, the crust of the 

 earth is bent, fissures are formed ; or, at any rate, the 

 continuity of the rocky layers is disturbed, and they are 

 rendered more or less porous, so that surface waters are 

 able to make their way deep in*o the bowels of the earth, 

 and to reach occasionally the heated deposits of metallic car- 

 bides, which may exist either in a separated condition or blended 

 with other matter. Under such circumstances it is easy to see 

 what must take place. Iron, or whatever other metal may be 

 present, forms an oxide with the oxygen of the water ; hydiogen 

 is either set free, or combines with the carbon which was 

 associated with the metal, and becomes a volatile substance — 

 that is, naphtha. The water which had penetrated down to 

 the incmdescent mass is changed into steam, a portion of 

 which finds its way through the porous substances with which 

 the fissures are filled, and carries with it the vapours of 

 the newly formed hydrocarbons, and this mixture of vapours 

 is condensed wholly or in part as soon as it reaches the 

 cooler strata. The chemical composition of the hydrocarbons 

 produced will depend upon the conditions of temperature and 

 pressure under which they are formed. It is obvious that these 

 may vary between very wide limits, and hence it is that mineral 

 oils, mineral pitch, ozokerit, and similar products, differ so greatly 

 from each other in the relative proportions of hydrogen and 

 carbon. I may mention that artificial petroleum has beer 

 frequently prepared by a process analogous to that described 

 above. 



Such is the theory of the distinguished philosopher, whc 

 has framed it, not alone upon his wide chemical knowledge, but 

 also upon the practical experience derived from visiting otificiallj 

 the principal oil-producing districts of Europe and America, 

 from discussing the subject with able men deeply interested ir 

 the oil industry, and of collecting all the available literature or 

 the subject. It is needless to remark that Dr. Mendeleeffs views 

 are not shared by every competent authority ; nevertheless the 

 remarkable permanence of oil-wells, the apparently inexhaustible 

 evolution ot hydrocarbon gases in certain regions, almost force 

 one to believe that the hydrocarbon products must be forming a; 

 fast as they are consumed, that there is little danger of thi 

 demand ever exceeding the supply, and that there is ever} 

 prospect of oil being found in almost every portion of the surface 

 of the earth, especially in the vicinity of great geological disturb 

 ances. Improved methods of boring wells will enable greate 

 depths to be reached ; and it should be remembered that, apar 

 from the cost of sinking a deep well, there is no extra expensi 

 in woiking at great depths, because the oil generally rises to thi 

 surface or near it. The extraordinary pressures, amounting t( 

 300 pounds per square inch, which have been measured in soml 

 wells seem to me to yield conclusive evidence of the imperm 

 bility of the strata from under which the oil has been forced i 

 and tend to confirm the view that it must have been fora 

 in regions far below any which could have contained orgJ 

 remams. 



The weights and measures in use in this country are £ 

 of considerable trouble and confusion. Besides the impd 

 measures, which are complicated enough, a great numbei 

 local units are in use, so that unwary strangers are not 

 quently deceived, or, at any rate, if they hope to e=cape fo 

 mistakes, have to apply themselves to the study of local custom; 

 In the scientific world, again, the metric system is now almo:| 

 exclusively used, and the same may be said of engineers ^, 

 manufacturers who have to do with foreign countries in wl^ 

 French measures are in vogue. The same difficulty surroB 

 the measurement of the power of motors. The unit of powe 

 indeed, from the nature of the case, common to the wl 



