bonic acid. This production of carbonic acid, therefore, adds to the dilatation occafioned by the evolution of hydrogenous gas.

6. There is not, by the action of the electric matter on carbonated hydrogenous gas, any generation of azotic gas.

7. Carbon, it appears, therefore, from the united evidence of these facts, is still to be confidered as an elementary body; that is, as a body with the compofition of which we are unacquainted, but which may nevertheless yield to the labours of fome future and more fuccessful analyst.

II.

Obfervations on Bituminous Substances, with a Defcription of the Varieties of the Elaftic Bitumen. By CHARLES HATCHETT, Efq. F.R.S. Lond. and Edin. F.L.S. &c.

THE

[Concluded from Page 209, Vol. II.]

HE characters of bitumen are much more apparent in turf and peat, than in the greater part of the foffil woods. Turf is well known to be composed of the parts of vegetables, fuch as fmall roots, twigs, &c. mixed with a portion of petroleum; and peat is the fame, excepting that it generally contains more of earthy matter, or that the vegetables have undergone a more complete decomposition.

The boggy nature of the places in which they are found, proves that a certain degree of maceration is necessary to form the bituminous matter which they contain; and I have already noticed, that every fact appears to demonftrate, that the bitumen is a product of those vegetables, the remains of which conftitute the other ingredient of turf and peat.

The different proportion of vegetable matter, of bitumen, and of earth, together with the different state of the bitumen, as well as the degree of perfection respecting the formation of it from the vegetable principles, contribute to alter the properties and characters of the compound, and thus produce varieties. It is believed that thefe fubftances have been materially concerned in the formation of pit-coal, and some eminent mineralogists maintain that there is an uninterrupted series which connects the varieties of turf and peat with those of coal *.

SECT. V.

LITTLE need be faid concerning those mixtures of bitumen with metals or their oxides which are sometimes called the bituminous ores of mercury, copper and iron, for they should rather be arranged with the adulterated or impure bitumens. Few of them contain the metallic ingredient in a proportion fufficient to cause the compound to be worked as an ore; and the only exception with which I am acquainted, is the substance found at Idria, in Carniolia, compofed of mercury mixed with bituminous matter, a quintal of which, according to Mr. de Born, affords from fifteen to twenty pounds of mercury t

* Man findet in der natur einen ununterbrochenen übergang von dem rafen und papiertorf durch den moor oder fumpftorf in den pechtorf, und von diesem in die braun schiefer und pechkohle.-Widenmann, p. 630. + Catalogue de la Collection des Foffiles de Mlle. de Raab, tom. ii. p. 294, 348, and 400.

SECT. VI.

New Species of Bitumen refembling India Rubber.

SECT. VI.

249

FROM the preceding obfervations it will appear, that although I have first mentioned naptha in order that I might be better understood in respect to the degree of connection prevailing between the bituminous substances; yet, to have followed them from their origin and the period of their formation, I fhould rather have begun with thofe fubftances which moft clearly point out how much the vegetable kingdom has contributed to the production of them, with the probable occafional concurrence of animal fubftances.

That the latter have contributed in fome meafure to the forming of bitumen, we can only infer from the veftiges and exuvia of animals, which fo commonly accompany bituminous fubftances: but no doubt can be entertained in refpect to vegetables; for it appears that bitumen is formed from them by long maceration, and by other proceffes at prefent unknown to us:

That when certain portions of vegetable matter remain undecompofed, and are mixed with the petroleum thus produced, the varieties of turf and peat are formed:

That wood in general contributes to the production of bitumen; but does not feem to retain it, after the formation of it, in fo confiderable a proportion as the foregoing fubstances:

That the bituminous matter thus formed, and occafionally feparated, is in different states according to the degree of infpiffation:

And lastly, with various proportions of carbonic and earthy matter, it forms jet, coal, and bituminous schiftus; and with metallic fubftances it produces thofe compounds called bitu.... minous ores.

SECT. VII.

ABOUT the year 1786 a new fpecies of bitumen was difcovered near Caftleton, in Derbyshire, which much resembles, in elafticity and colour, the fubftance known by the name of cahout-chou, or Indian rubber.

M. de Born was, I believe, the first who mentioned it *; but, as he appears to have known only one variety of this fingular substance, I am induced to hope that a description of many other varieties, which have fince been found, will not be unacceptable to this Society.

The elastic bitumen, which resembles the cahout-chou, was firft difcovered in the cavities of a vein in the lead-mine called Odin, which is near the bafe of Mamtor, to the north of Caftleton. The ore of this mine (which is fuppofed to be one of the most ancient in England) is galena, accompanied by fluor, calcareous and heavy fpars, quartz, blende, calamine, felenite, afphaltum, and the elastic bitumen, although the latter is now rarely found t. Another species of the elaftic bitumen has within about three years been found in a neighbouring rivulet; but I fhall not at prefent notice it, as I intend first to defcribe the varieties of that which was first discovered, and which refembles the cahout-chou. In order to do this with more perfpicuity, I fhall defcribe the fpecimens belonging to my collection, according to the mode in which I have arranged them.

Catalogue de la Collection de Mlle. de Raab, tom. ii. p. 77.

+ I am indebted to the ingenious Mr. White Watson, of Bakewell, for much information respecting the local circumftances which attend this bitumen.

VOL. II.-SEPT. 1798.

Kk

SPECIES

250

New Species of Elaftic Bitumen.

SPECIES THE FIRST.

A, No. 1.-Elaftic bitumen of a yellowish brown colour, part of which is almost liquid like petroleum, and adheres to the fingers; the other part is of a darker colour, of a mammillary form, does not adhere to the fingers, and is soft and elastic. This is on a grey bituminous limeftone, with white calcareous fpar in the figure of hexaedral pyramids, forming that which is called the dog-tooth spar.

A, No. 2.-Bitumen of a yellowish brown, partly liquid, and partly elaftic, which, however, adheres to the fingers; on pale grey limestone, with cryftals of white fluor fpar, blende, and galena.-On another part of the limestone are some globules of bitumen of a reddish brown, perfectly hard and brittle,

A, No. 3.-Dark brown bitumen of a stalactitical form, hard, but in fome degree elastic.

A, No. 4.-Bitumen of a reddish brown, in the form of globules, fome of which are elastic, and others hard: on brownish-grey limestone, accompanied by cryftallized white fluor, dogtooth calcareous fpar, and pyrites in fmall cryftals, fome of which are on the furface of the globules of bitumen.

A, No. 5.-The fame of a darker brown, of a stalactitical form, hard and brittle; on pale brown calcareous fpar, impregnated with bitumen.

A, No. 6.-Bitumen of a dark reddish brown, very hard; on pale brown sparry stinkftone, with grey limestone, in which are fome coralloides.

A, No. 7.-Bitumen of a dark yellowish brown, elastic, but very soft, fo that it adheres to the fingers.

A, No. 8.-The fame thinly spread over grey sparry stink-stone.

A, No. 9.-Bitumen of a brownish olive colour, which becomes reddish brown by the air, but when opposed to the light it appears semi-transparent, and of a yellowish brown inclining to orange. It is foft, very elastic, and (when recently cut) adheres to the fingers.

A, No. 10.-The fame of a darker brown, and harder in a small degree. The specific gravity of this specimen is 0,9053; water being estimated at 10,000 (q. 1,000?) at temp. 60°. A, No. 11.-Bitumen of a dark brown, harder than the former. This exactly resembles the cahout-chou in the degree of elasticity, and in the property which it poffelles of removing the traces of black-lead.

A, No. 12.-The fame, but rather harder.

A, No. 13.—The same of a blackish brown, which is flightly elaftic when the weather is warm, but is brittle when cold.

A, No. 14.-The fame of a blackish brown, nearly black, which scarcely poffeffes any elasticity; it breaks, and resembles asphaltum în luftre, colour and fracture.

A, No. 15.-The fame of a reddish brown, perfectly hard and brittle. The characters of afphaltum are complete in this specimen. The specific gravity is 10,233. (4. 1,233?) The other species of elastic bitumen, which I fhall distinguish by the letter B, has been found during the last three years in a rivulet which runs at the bafe of Mamtor, from west to east, at a small distance from Odin mine. The varieties of it, in my poffeffion, are as follow:

Obfervations on the Elafticity of Bitumen,

SPECIES

THE SECOND.

251

B, No. 1.-Elaftic bitumen, which, recently cut, exactly resembles fine close cork in colour and texture, but, by the air, in a few days it becomes of a pale reddish brown.--This forms a thin coat, which completely covers a mafs of elastic bitumen, which is foft, and of a brownish olive colour, like A, No. 9.

B, No. 2.-The fame, excepting that the coat or cruft is much thicker.

B, No. 3.-The fame, but the coating is thicker than that of No. 2, and the brownish olive-coloured bitumen much less in quantity.

B, No. 4.-The fame, excepting that the greater part of the mafs resembles cork, fo that only a very small nucleus of the brown bitumen remains *.

B, No. 5.-The fame, excepting that the bitumen, which is coated, is in the state of asphaltum. The specific gravity of this specimen is 0,9881.

B, No. 6.—Elastic bitumen, the whole mafs of which resembles fine cork.-The fpecific gravity is 0,9748.

B, No. 7.-The fame, but friable, and apparently paffing by decomposition into an ochraceous coloured powder.

THE varieties of the firft fpecies of the elaftic bitumen, or that which is like the cahoutchou, evidently appear to be formed from a naptha or petroleum, which, like that which produces the other fimple bituminous fubftances formerly mentioned, is susceptible of various degrees of infpiffation.

All the varieties of the firft fpecies, from No. 1, to No. 15, may be regarded as thus formed; for in these we can trace all the modifications comprehended between petroleum and afphaltum with this difference, that the intermediate modifications of this fpecies have the remarkable property of elasticity which is the most complete in the variety which occupies the middle place between petroleum and asphaltum.

:

The second species B, or that which resembles cork, appears so different from that marked A, that it is not at first easy to conceive how they are connected, or at least the difficulty muft appear great to those who have only feen fpecimens of each fpecies complete in their refpective characters. But, from an attentive examination of many specimens, and particularly of those which I have described, I am convinced that the varieties of the species B are only modifications of the fpecies A, produced probably by long maceration in the water of the rivulet in which this fpecies is found, to the effects of which we may, with some appearance of reason, add the viciffitudes of the seasons, of air, and of the weather in general, as well as thofe of reiterated moisture and dryness occafioned by the rife and fall of the water of the rivulet; and what seems to corroborate this opinion is, that the sübftance, like cork, incrufts the fpecies A, and appears to be only a change which has penetrated deeper into the fubftance of it in proportion to the duration of the causes which I have mentioned, fo that at length the original substance no longer remains in its primitive state. I do not believe, however, that this change arifes from any alteration in the conftituent principles, but merely

One of the specimens in my poffeffion, fimilar to B, No. 4. weighs between 13 and 14 pounds.

252

Obfervations and Experiments on Elaftic Bitumen.

from a partial and minute dif-union or difintegration of the particles of the original substance, as both species melt into one which is perfectly fimilar. I muft alfo add, that the fpecies A burns cafily, and with rapidity; but the fpecies B burns with fome difficulty, and crackles as if it had imbibed a quantity of water.

I have remarked, when the different varieties of the elaftic bitumen were melted, that they completely loft the elastic property, and a quantity of air or gas appeared to be difengaged, particularly from the fpecies B. I also observed, that the substances which remained after this operation, corresponded, in respect to confiftence, with those which had been employed, as the following table will fhew:

A, No. 7 and 8...... produced a thick liquid petroleum, not apparently different from that which is commonly known.

A, No. 11 and 12....

B, No. 6....

A, No. 13

A, No. 14

produced a thicker petroleum, approaching to mineral tar.

produced mineral tar.

produced the fame, approaching to mineral pitch.

produced mineral pitch.

and 15... did not fuffer any change, but remained as at firft, with all the characters of afphaltum.

From what I have related, I fufpect that the elaftic property is occafioned by the interpofition of very minute portions of air or fome other elaftic fluid between the parts of the bitumen, and that this takes place by reafon of fome unknown caufe at the time of forma tion; but when these bitumens are melted, the elaftic fluid is liberated, and the mass lofes that fine spongy texture which I suspect to have been the cause of the elaftic property

Derbyshire is well known as a country which exhibits, in the most striking manner, the remarkable changes which our globe has fuffered. In every part of it, the most indifputable evidences appear of fome great and extraordinary revolution; and there is not any place where extraneous foffils, fuch as the remains and impreffions of vegetables and animals, are - more abundant.

Bitumen, in other countries, is most commonly found where these present themselves and, in like manner, there are few countries which abound so much with bitumen as Derby. fhire.

Whoever has examined the limestone rocks about Matlock, and most other places in this >county, must be convinced of the truth of this affertion.

The limestone and calcareous spars alfo, where the elastic bitumen is found, are, for the greater part, in the fame ftate; fo that no doubt can be entertained but that this bitumen has had the fame origin as thofe which are more generally known; and it would undoubtedly have been confounded with them, had it not been difcovered when paffing from the liquid to the folid state.

*The laftic bitumen, A, No. 9. when digefted in fulphuric ether in a temperature of about 55°, is partly diffolved. The folution is yellowish brown when oppofed to the light; but, when otherwise viewed, is like the bitumen, that is, of a brownish olive colour. By fpontaneous evaporation, the etheric folution leaves a yellowish brown bitumen, which is totally devoid of elafticity. The undissolved portion (like the cahout-chou under fimilar circumftances) is foftened, and is much increased in bulk.

The fpecies B, No. 6. cut into very thin flices, communicates a yellow tinge to fulphuric ether; in other .refpects it is but little affected.

The