of the sulphuric acid is purely molecular, the ultimate chemical composition of the paper-cellulose-remaining unchanged. [As already stated by Poumarède and Figuier loc. cit. and by J. Barlow, Proc. of the Royal Inst. 1857, ii. 411]. The result of the momentary action of sulphuric acid in this instance is comparable with that which a longer action of this acid upon woody fibre produces, viz.: formation of dextrine, a substance well known to be isomeric with cellulose. Indeed, the vegetable parchment may be regarded as a middle term between dextrine and cellulose.

The samples of parchment-paper examined by Hofmann [and by Barlow] contained no trace of free sulphuric acid; small portions of sulphate of lime and of sulphate of ammonia being the only soluble impurities present.

There is no apparent reason why the parchment-paper should not endure for an indefinite length of time. It is evident that if its destruction were dependent in any way upon the chemicals used in preparing it, decomposition would set in at once. Nothing of the kind occurs, however. Specimens of the factitious parchment which have been in Hofmann's possession during four years being undistinguishable from those recently prepared.

From experiments made in order to ascertain the strength of parchment-paper, as compared with that of true parchment and of unsized paper, it appeared that while strips of unsized paper broke when subjected to a weight of 15 or 16 pounds, similar strips of vegetable parchment supported 74 lbs., and those of ordinary parchment 75 lbs., before breaking. The cohesive force of unsized paper is thus increased five-fold by the treatment with sulphuric acid. It was also proved by experiment that for equal weights of the two substances parchment-paper exhibited about three-fourths the cohesive power of animal parchment. It also appeared that while the strength of strips of parchment paper taken from different sheets was nearly constant, that of strips of animal parchment, even when cut from a single piece, was extremely variable, owing to the differences in thickness to which it is liable.

Parchment-paper although not quite so strong as ordinary parchment, is nevertheless more capable than the latter of withstanding the action of chemical agents, and especially of resisting the action of water; it may be left in this liquid for days, or even boiled in it, without undergoing any change, other than the increase of volume already alluded to, its original cohesion, and indeed all its properties being regained on drying. As is well known, animal parchment is soon converted into glue when boiled with water.

Since the parchment-paper contains no nitrogen, it is much less liable than ordinary parchment to putrefy when exposed to moisture, and will probably be less subject to the attacks of insects. Not only may the new parchment be substituted for that ordinarily employed for legal documents, &c.; but from its cheapness it will probably soon be used for ledgers and other important records-possibly for bank-notes-instead of the more perishable paper now employed. ["It will take the place of ordinary paper in school books, and other books exposed to constant wear." "It also promises to be of value for photographic purposes, and for artistic uses, in consequence of the manner in which it bears both oil and water

color."-Barlow.] Its strength and power of resisting the action of moisture seem also specially to adapt it for the use of architects and engineers -particularly for working-plans liable to receive rough usage; also for the envelopes of letters and for cartridges. In thin leaves it affords an admirable tracing paper. As a material for binding books it will without doubt be extensively used. The ease with which it receives both printers' and ordinary writing ink is remarkable. For chemical laboratories it affords a most convenient material for fitting together retorts, condensers, and the like; while its power of resisting the fluids used in galvanic batteries suggests that it may be useful for diaphragms, &c. It is already used by tons, instead of bladder, as a covering for jars containing preserves, marmelades, etc.

Parchment paper has been successfully manufactured on the great scale for a year or more by the firm of De LaRue, the numerous difficulties which presented themselves having been fully overcome by the perseverance of one of its members-the distinguished chemist Warren De LaRue. [Specimen sheets of the parchment-paper accompany Hofmann's memoir.-F. H. S.].

2. Weighing of Moist Precipitates; by FERDINAND F. MAYER.-Mr. Ch. Mène, of Creusot,* gives a mode of weighing which does away to a great extent with the tediousness and difficulties attending the drying of many precipitates, especially in volumetric analysis. He washes the precipitate thoroughly by decantation, and then introduces it carefully into a bottle, the exact weight of which, when filled with distilled water at a certain temperature, is known. Since the precipitate is heavier than water, the bottle when filled again will weigh more than without the precipitate, and the difference between the two weights furnishes the means of calculating the weight of the precipitate.

In case the precipitate settles but slowly it may be collected on a filter, and together with the filter, after washing, be introduced into the bottle, in which case the weight of the filter and its specific gravity, supposing any difference should exist between its own and that of water, is to be taken in account. Precipitates soluble in or affected by water may be weighed in some other liquid.

This method, of which the above are the outlines, is spoken of in the Jahresbericht der Chemie for 1858† in rather disparaging terms, and I consider it not more than justice to the method, if not also to Mr. Mène, to prove its correctness, the more so as I have applied the principle on a large scale as far back as 1855.

I engaged in that year in the manufacture of carbonate of lead from refuse sulphate of lead, by treating the latter in a pulpy condition with carbonate of soda. The sulphate of lead I used contained very varying proportions of water and soluble impurities, from which latter it had first to be freed by washing. It was then in the state of a thin pulp, and the difficulty was to find the amount of dry sulphate of lead, as it was a matter of importance to use as little carbonate of soda, and to obtain as pure a carbonate of lead and sulphate of soda as possible. This could only be done by weighing it as a whole, or in portions; but as the * Journal de Pharmacie et de Chemie, Oct. 1858.

Jahresbericht der Chemie, by Will and Kopp, for 1858, p. 4.

drying of a tubful of sulphate of lead (from 500 to 1200 pounds) was impracticable, and sampling not less so, since the upper strata contained a much larger proportion of water than the lead at the bottom: I contrived the following method, which enabled me to leave the management of the process in the hands of a workman.

I took a strong oaken pail, weighing eight pounds when empty, and caused a black mark to be burnt in horizontally around the inside of the pail, two inches below the rim, up to which mark it held twenty pounds of water. I reasoned as follows: The specific gravity of sulphate of lead being 6-3, the pail if filled up to the mark would hold 126 pounds of pure sulphate of lead. The specific gravity of water being 5.3 less than that of sulphate of lead, it followed that if there was one pound of water in the pailfull of moist sulphate, the pail would weigh 5.3 pounds less than 126 (+8, the tare of the pail) 120.7 (+8); if there were two pounds of water present, the weight would be 1154 (+8), and so on. This enabled me to calculate a table, giving in one column the actual weight of the pail when filled with moist sulphate, and opposite in a second column, the amount of dry sulphate corresponding to the gross weight. The weight of dry sulphate was thus found as accurately as could be desired, although the amounts varied in practice from 30 to 105 pounds.

It is nothing but an application of the Archimedean theorem, that, when a solid body is immersed in a liquid it loses a portion of its weight, equal to the weight of the fluid which it displaces, or to the weight of its own bulk of the liquid.

This, as I suppose, is precisely the principle applied by Mr. Mène. The precipitate he obtains by a certain chemical manipulation is a substance of known composition and specific gravity. Supposing it to be sulphate of lead, and the bottle, when filled with water at the normal temperature, to weigh 70 grammes=50 grammes of water, and 20 for tare. After introducing the precipitate and filling again with water it weighed 7106 grammes. Now, as the specific gravity of sulphate of lead is 6.3, or as the weight of a cubic measure of sulphate of lead is 6-3 times that of a cubic measure of water, and as the space of one part by weight of water is taken up by 63 parts by weight of sulphate of lead, it follows that the quantity of sulphate of lead in the bottle, which has taken up the space of one part by weight of water, increases the original weight of the bottle (filled with pure water) by 5.3. To find the amount of water displaced it is only necessary to divide the overweight (1.06 grammes) by 53 02, which, added to the overweight 1:06+0.2 gives 1.26 grammes as the weight of the precipitate.

Hence the rule, which is of great convenience in volumetric analysis, that to find the weight of a moist precipitate, which is a compound of known specific gravity, weigh it in a specific gravity bottle or some other vessel of known weight when filled with water, or any other liquid, at the normal temperature, again fill it with the water or other liquid, divide the excess of the new weight by the specific gravity of the substance, less that of the water or other liquid (that of water being 1) and add the quotient to the overweight, which gives the weight of the precipitate.

The editor of the Jahresbericht appears to have overlooked the fact that the precipitates weighed in this manner are definite compounds, the specific gravity of which is well ascertained.

SECOND SERIES, Vol. XXIX, No. 86.-MARCH, 1860.

The principle I have exemplified above may not be novel; but as I have never met with it, chemists, as well as manufacturers (especially of colors), will probably also find it of interest, and certainly highly practicable and easy of execution.

36 Beekman street, New York, Feb. 3d, 1860.

3. New Chemical Journal.-The Chemical News (with which is incorporated the Chemical Gazette), edited by WILLIAM CROOKES. London: Weekly. Price 3d., stamped 4d. 8vo. 12 p. each number. This new Journal commenced on the 10th of December last, and eight numbers have already reached us. The contents are divided under Scientific and Analytical Chemistry, Technical Chemistry, Pharmacy, Toxicology, &c., Proceedings of Societies, Notices of Patents, Correspondence, Scientific Notes and Queries, Laboratory Memoranda, Miscellanies, and Answers to Correspondents. Mr. Crookes is favorably known by several valuable researches, and thus far has shown good judgment and spirit as an editor. His verbatim reports of the late lectures of Dr. Faraday (the Holiday lectures) at the Royal Institution, attest his appreciation of the true sources of vitality for such a journal.

4. American Druggists' Circular and Chemical Gazette; N. Y. Feb. 1860. 4to.-Although chiefly special and wholly technical in its objects, this Journal (which has now reached its 4th volume, whole number 38) is conducted by Mr. Mayer and others, in a manner to entitle it to rank as a valuable coadjutor in technical chemistry.

II. GEOLOGY.

1. On some of the Igneous Rocks of Canada; by T. STERRY HUNT, F.R.S. (In a letter to one of the editors, dated Jan. 1860.)-There occurs in the district of Montreal a series of isolated hills running nearly east and west for a distance of ninety miles along the line of an undulation which has disturbed the lower Silurian strata. These hills, which often cover considerable areas, consist of igneous rocks which have apparently been solidified under a considerable pressure, and have subsequently been exposed by the denuding action which has removed from around them the soft and unaltered paleozoic strata. The names of these mountains counting from the west are Rigaud, Mount Royal, Montarville, Beloeil, Rougemont, Yamaska, Shefford and Brome, to which we may add Monnoir a similar mass lying somewhat to the south of Belœil.

I am now engaged in the study of the various rocks composing these mountains, which offer great diversities in lithological character and composition. Prominent among them we may mention the trachytes, which in their various types of compact, granular, porphyritic and granitoid are abundant. The mountains of Brome and Shefford appear to be made up entirely of a granitoid trachyte, which consists of crystalline orthoclase, without quartz, and with small portions of hornblende or mica, sphene and magnetite. The orthoclase in a great number of these rocks which I have analyzed contains like sanidin a large proportion of soda. The other varieties of trachyte which occur in veins and dykes often contain a portion of carbonates amounting to from 6.0 to 180 p. c. and consisting chiefly of carbonate of lime with some magnesia and

iron. Some of these rocks pass into phonolites through the admixture of a silicate which gelatinizes with acids and has the composition of natrolite. This mineral in one case amounted to more than 400 p. c. of the rock, the remainder being orthoclase with a small amount of carbonates.

A large part of the mountain of Yamaska consists of a coarsely crys→ ⚫talline diorite the feldspar of which approaches anorthite in composition, while an apparently similar diorite, which makes up the mass of Monnoir, contains oligoclase in large crystals. Other diorites from this series contain labradorite; mica and sphene, in small quantities, are often present.

Dolerites are also abundant, and sometimes pass, owing to a scarcity of feldspar, into an augite rock, generally with ilmenite and magnetite. A fine-grained dolerite from Rougemont contains abundance of crystallized olivine, and a large part of Montarvilles consists of a remarkable granitoid rock, made up of a crystalline feldspar, in some parts at least labradorite, with sparsely disseminated crystals of black augite, a little brown mica, and a great abundance of crystals of honey-yellow olivine, which amount to more than 450 p. c. of the mass. The composition of this olivine I have found to be silica 37-17, magnesia 39-68, protoxyd of iron 22.5499.39.

Many of these diorites and dolerites, except in their lithological structure, closely resemble the stratified rocks made up of anorthie feldspar, with hornblende and pyroxene, and containing magnetite and ilmenite, which are so abundant in the Laurentian system, suggesting the notion that the intrusive masses may be nothing more than these stratified rocks displaced and injected among the Palæozoic strata. Durocher has already pointed out a similar resemblance between the intrusive rocks of some parts of Scandinavia, and the subjacent gneiss.-(Bul. Soc. Geol. France, [2] vi, 33.)

The granitoid trachytes as well as the dolerites, diorites and peridotite (olivenite rock) make up mountain masses, while the earthy and porphyritic trachytes and the phonolites are generally found cutting the above, and the adjacent strata. The absence of quartz or of any excess of silica from all these rocks is a remarkable feature. Farther to the east, however, intrusive granites are very abundant; these penetrate the Devonian strata but are older than the carboniferous. Quartziferous plutonic rocks are also abundant in the county of Grenville, where they penetrate the Laurentian series. These plutonic rocks consist of dolerites, syenites and eurites, which are in their turn cut by dykes of very beautiful porphyries. The base of these is jasper-like, black, red or green in color, and encloses crystals of red orthoclase and occasional grains of quartz. The analysis of the base shows it to consist of the elements of orthoclase with an excess of silica and a little oxyd of iron. The syenites are cut by large veins of chert, and in the vicinity of these have been changed into a sort of kaolin from a decomposition of the feldspar, which may have been the source of the silicious accumulations. This group of igneous rocks, which is overlaid by the Potsdam sandstone is very unlike those which we find penetrating the palæozoic

strata.