PETROLEUM is one of the most widely distributed substances in Nature, but the question how it was originally produced has never yet been satisfactorily determined, and continues a problem for philosophers. In 1889 the total production exceeded 2,600,000,000 gallons, or about 10,000,000 tons, and, at fourpence per gallon, was worth about £44,000,000, while the recognition of its superior utility as an economical source of light, heat, and power, steadily increases; but, notwithstanding its importance in industry, the increasing abundance of the foreign supply, and the ever widening area of production, practical men in England continue to distrust its permanence; and owing to the mystery surrounding its origin, and the paucity of indications where and how to undertake the boring of wells, they hesitate to seek for it in this country, or even to extend the use of it whenever that would involve alterations of existing machinery. The object of this paper is to suggest an explanation of the mystery which seems calculated to dissipate that distrust, since it points to very abundant stores, both native and foreign, yet undiscovered, and even in some localities to daily renovated provisions of this remarkable oil.

The theories of its origin suggested by Reichenbach, Berthelot, Mendeleeff, Peckham, and others, made no attempt to account for the exceeding variety in its chemical composition, in its specific gravity, its boiling points, &c., and are all founded on some hypothetical process which differs from any with which we are acquainted; but modern geologists are agreed that, as a rule, the records of the earth's history should be read in accordance with those laws of Nature which continue in force at the present day, e.g., the decomposition of fish and cetaceous animals could not now produce oil containing paraffin. Hence we can hardly believe it was possible thousands or millions of years ago, if it can be proved, that any of the processes of Nature with which we are familiar is calculated to produce it.

The chief characteristics of petroleum strata are enumerated as :

I. The existence of adjoining beds of limestone, gypsum, &c.

II. The evidence of volcanic action in close proximity

to them.

III. The presence of salt water in the wells.

I. All writers have noticed the presence of limestone close to petroleum fields in the United States and Canada, in the Caucasus, in Burmah, &c., but they have been most impressed by its being "fossiliferous," or shell limestone, and have drawn the erroneous inference that the animal matter once contained in those shells originated petroleum; but no fish oil ever contained paraffin. On the other hand, the fossil shells are carbonate of lime, and, as such, capable of producing petroleum under conditions such as many limestone beds have been subjected to in all ages of the earth's history. All limestone rocks were formed under water, and are mainly composed of calcareous shells, corals, encrinites, and foraminiferathe latter similar to the foraminifera of "Atlantic ooze " and of English chalk beds. Everywhere, under the microscope, the original connection of limestone with organic matter-its organic parentage, so to speak, and cousin.

* Abstract of a Paper read before the British Association, Cardiff Meeting, 1891, Section G.

oil.

II. As evidence of volcanic action in close proximity to petroleum strata, the mud volcanoes at Baku and in Burmah are described, and a sulphur mine in Spain is mentioned (with which the writer is well acquainted), situated near an extinct volcano, where a perpetual gasflame in a neighbouring chapel and other symptoms indicate that petroleum is not far off. While engaged in studying the geological conditions of this mine, the author observed that Dr. Christoff Bischoff records in his writings that he had produced sulphur in his own laboratory by passing hot volcanic gases through chalk, which, when expressed in a chemical formula, leads at once to the postulate that, in addition to sulphur, ethylene and all its homologues (CnH2n), which are the oils predominating at Baku, would be produced by treating2, 3, 4, 5 equivs. of carbonate of lime (limestone) with 2, 3, 4, 5 sulphurous acid (SO2) and 4, 6, 8, 10 sulphuretted hydrogen (H2S); and that marsh-gas and its homologues, which are the oils predominating in Pennsylvania, would be produced by treating

So that these and all their homologues, in fact petroleum in all its varieties, would be produced in Nature by the action of volcanic gases on limestone.

But much the most abundant of the volcanic gases appear at the surface as steam, and petroleum seems to have been more usually produced without sulphurous acid, and with part of the sulphuretted hydrogen (H2S) replaced by H2O (steam) or H2O2 (peroxide of hydrogen), which is the product that results from the combination of sulphuretted hydrogen and sulphurous acid(H2S+SO2=H2O2+2S).

It is a powerful oxidising agent, and it converts sulphurous into sulphuric acid. Thus

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resulting from the increase in regular gradation of the same constituents.

It is explained that these effects must have occurred, not at periods of acute volcanic eruptions, but in conditions which may be, and have been observed at the present time, wherever there are active solfataras or mud volcanoes at work. Descriptions of the action of solfataras by the late Sir Richard Burton and by a British Consul in Iceland are quoted, and also a paragraph from Lyall's "Principles of Geology," in which he remarks of the mud volcanoes at Girgenti (Sicily) that carburetted hydrogen is discharged from them, sometimes with great violence, and that they are known to have been casting out water, mixed with mud and bitumen, with the same activity as now for the last fifteen centuries. Probably at all these solfataras, if the gases traverse limestone, fresh deposits of oil-bearing strata are accumulating, and the same volcanic action has been occurring during many succes sive geological periods and millions of years; so that it is difficult to conceive limits to the magnitude of the stores of petroleum which may be awaiting discovery in the subterranean depths.*

Gypsum may also be an indication of oil bearing strata for the substitution in limestone of sulphuric, for carbonic acid can only be accounted for by the action of these hot sulphurous gases. Gyp-um is found extensively in the petroleum districts of the United States, and it underlies the rock salt beds at Middlesboro', where, on being pierced, it has given passage to oil-gas, which issues abundantly, mixed with brine, from a great depth.

III. Besides the space occupied by "natural gas," which is very extensive, 17,000 million gallons of petroleum have been raised in America since 1860, and that quantity must have occupied more than 100,000,000 cubic yards, a space equal to a subterranean cavern 100 yards wide by 20 feet deep, and 82 miles in length, and it is suggested that beds of "porous sandstone "could hardly have contained so much; while vast receptacles may exist, carved by volcanic water out of former beds of rock salt adjoining the limestone, which would account for the bine that usually accompanies petroleum. It is further suggested that when no such vacant spaces were available, the hydrocarbon vapours would be absorbed into, and condensed in, contiguous clays and shales, and perhaps also in beds of coal, only partially consolidated at the time.

There is an extensive bituminous limestone formation in Persia, containing 20 per cent of bitumen, and the * Professor J. Le Conte, when presiding recently at the International Geological Congress at Washington, mentioned that in the United States extensive lava floods have been observed covering areas from 10,000 to 100,000 square miles in extent, and from 2000 to 4000 feet deep. We have similar lava flows and ashes in the North of England, in Scotland, and in Ireland, varying from 3000 to 6000 feet in depth. In the Lake District they are nearly 12,000 feet deep. Solfataras are active during the intermediate, or so-called "dormant," periods which occur between acute volcanic eruptions

theory elaborated in the paper would account for bitumen and oil having been found in Canada and Tennessee embedded in limestone, which fact is cited by Mr. Peckham as favouring his belief that some petroleums are a " product of the decomposition of animal remains." Above all, this theory accounts for the many varieties in the chemical composition of paraffin oils in accordance with ordinary operations of Nature during successive geological periods.

ON A COMBINATION OF WET AND DRY METHODS IN CHEMICAL ANALYSIS.

PART I.

By W. E. ADENEY, F.I.C., Assoc.R.C.Sc.I., Curator, Royal University of Ireland; and T. A. SHEGOG, A.I.C., Assoc. R.C.Sc.I., Assist. Chemist, Royal College of Science, Dublin. (Concluded from p. 187.)

SECOND SERIES OF EXPERIMENTS. ANOTHER Series of experiments was now made differing from the preceding ones in this respect. In all cases the substance and fluxes were fused together in a shallow cavity in charcoal, the oxidising flame being employed, the beads on cooling were transferred to a cavity of the usual shape and size, metallic silver added in the form of a button, and the whole heated in the reducing flame.

Difficultly Reducible Metallic Oxides.

Three decigrms. of each substance, fused with twelve decigrms. of borax in the oxidising flame on charcoal, then nine decigrms. (in the case of cobalt, twelve decigrms.) of silver in the form of a button added, and the fusion continued, the reducing flame being employed.

Iron (Ferrous Sulphate).—The metallic bead became quite infusible, but fused when the flame was removed; a very faint trace of iron was found in the metallic bead.

Cobalt (Cobalt Chloride).—The metallic bead was difficultly fusible on cooling; it flattened out in the way already described for cobalt (see First Series of Experi ments). It was found on testing to contain a small quantity of cobalt.

Aluminium (Aluminium Phosphate).-The metallic bead was somewhat infusible. Throughout the fusion a considerable quantity of metallic scale appeared on the glass bead. On testing the metallic bead, aluminium was found present.

Chromium (Chromium Nitrate).-The metallic bead was very difficultly fusible; on solidifying, it flattened out as already described for cobalt and chromium (see First Series of Experiments). On testing, a small quantity of chromium was found present.

From the Scientific Proceedings of the Royal Dublin Society.

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The fusion requires great care, and must be cooled in coal-gas. A very minute trace of antimony was found in the borax bead.

The fusion went well, though the metallic bead was somewhat difficult to fuse. The assay was cooled in coal-gas. Although every care was taken, it was found impossible to entirely reduce the tin. The glass bead was quite transparent. An experiment was made, using the same quantities of stannic oxide and borax; but, instead of silver, 12 decigrms. of metallic lead were added. This was unsuccessful, as the tin showed little tendency to alloy with the lead. The fusion went very well, but was found to require great care. It was cooled in coal-gas. The borax bead was found to contain a trace of lead, but so small as to be inappreciable. Volatilisation of arsenic occurred at the beginning of the fusion, but soon ceased. The fusion went easily, and a perfectly transparent glass bead was obtained. The assay was cooled in coal-gas. The glass bead was found to contain a scarcely detectable quantity of arsenic.

The silver remained easily fusible.

The fusion went very satisfactorily. It was cooled in coal-gas. A small quantity of bismuth was found on testing the glass bead.

The fusion requires care. The borax bead was of a pale bottle green colour (proved to be due to iron). On testing the glass bead with sulphuretted hydrogen a very slight colouration was observed. The fusion went fairly well, no fumes of arsenic were seen, and its volatilisation could only be detected by the garlic odour observed. The metallic bead was somewhat infusible, remaining all the time in a viscous state. The glass bead was tested for arsenic and nickel, and a mere trace of each was found present.

The fusion went well, both beads were easily fusible. The borax bead contained a mere trace of nickel.

It now only remains for us to make a brief reference to what has been done towards the solution of the third of the questions we wished to settle, namely, whether or not, when complex substances are fused with borax and sodium carbonate in the manner described, the constituent metals behave as in simple compounds.

In Dr. Davoren's estimations of nickel and cobalt by this method, no difficulty was experienced in effecting a complete separation; the nickel was entirely reduced, and all the cobalt was found in the glass bead. From this it was thought that the presence of an easily reducible oxide might entirely prevent the reduction of a difficultly reducible oxide. It seemed probable that if this were found to be the case with bodies so allied in chemical properties as nickel and cobalt, it would in all probability be true of the other oxides; experiments were therefore made with salts of these metals.

The salts were mixed with borax, and fused in the oxidising flame; no silver was used. The side of the glass bead which had cooled in contact with the charcoal was invariably found covered with a layer of reduced metal. When the proportions of nickel to cobalt in the mixture was greater than 1 to 1, the reduced metal was entirely nickel. When, however, the cobalt preponderated in the mixture, a small quantity was always reduced with the nickel.

It will be seen that a considerable number of experi ments are yet required, more especially to ascertain the behaviour of complex substances when treated in the way suggested by us; and it was our original intention to complete the necessary experiments before publishing any results of our investigation. In the midst of our work, however, one of us, having been elected to the office of Curator in the Royal University, had to resign his position in the Royal College of Science. We have since found it impossible to continue the work jointly, and we have therefore thought it advisable to publish an account of the work which has been already done.

The investigation will be carried on by one of us.