economically obtained by employing potash in the process for forming the ferrum præcipitatum.

To attempt a definition of his remark on the preparations of iron, would be Aquam arare, wherefore I shall be obliged, if favoured with information, as to its abstract tendency. What must be the inference of an assertion like the following? "That in the preparations of iron, there have been some alterations which are to be considered as amendments; but I am apprehensive that the good which has been done is more than counterbalanced by the omission of improvements, or the commission of errors." Surely, if in the formula, that is, such as have been altered, amendments have taken place, how can we ascribe to the College a want of ability, or the commission of error?

My remark relative to the ferri subcarbonas, will be seen in the note on sulphate of potash.

The acidum aceticum fortius diluted with water does not answer for the purpose of making the liquor plumbi subacetatis. I have frequently tried it, and ever been unsuccessful, for as soon as it assumes the density, as required in the Pharmacopoeia, it becomes opaque, which cannot be removed by filtration.

Anticipating the insertion of this paper in the Annals of Philosophy, by the which an elucidation of the several paradoxes complained of may be obtained,*

I remain very respectfully, Gentlemen,

Your most obedient servant,

G. WHIPPL

E

ARTICLE XIV.

Proceedings of Philosophical Societies.

ROYAL SOCIETY.

THIS Society re-assembled on the 18th of November; when Douglas C. Clavering, Esq. Capt. R. N. was admitted Fellow, and the Croonian Lecture, by Sir E. Home, VPRS. was read: it related to Mr. Bauer's discovery of nerves on both the fœtal and maternal surface of the Placenta: a paper, by the same author, as also read, On the Changes undergone by the Ovum of the wFrog, during the production of the Tadpole. We shall give some account of these papers in the next number of the Annals.

LINNEAN SOCIETY.

The first meeting of this Society for the present session took place on Nov. 2; when W. J. Broderip, Esq. was admitted

* I shall probably take some notice of this communication in the next Number.R. P.

Fellow, and a paper was read, On three Species of Birds, one hitherto undescribed, and the others new to the Ornithology of the British Islands; by N. A. Vigors, Jun., Esq. FLS. We shall present a report of this paper in our next.

GEOLOGICAL SOCIETY.

Nov. 5.-A paper was read entitled "Observations on a Comparison between the Beds below the Chalk in the Isle of Wight, and in the Counties of Surrey, Kent, and Sussex;" by Thomas Webster, Esq. Sec. G. S.

Mr. Webster stated, that in a late visit to the Isle of Wight, he had been so fortunate as to discover a rock of the same nature as the calciferous sandstone of Hastings, a circumstance that has furnished him with a fixed point, by means of which he had been enabled to compare the beds in the Isle of Wight with those of the south-east part of England more correctly than had been done before; and he presented a table of what he considered as the equivalent beds in these two places. He imagined that these equivalents had been hitherto stated erroneously by several geologists; and he attributed this chiefly to the following causes-1st, The imperfect state of the science of geognosy which had not as yet established fixed principles of classification: 2dly, The want of acknowledged types of beds or formations, to which all other parts might be referred: 3dly, The difficulties attending actual examinations, arising from the deficiencies or want of continuity of some beds, and the variation in the composition and structure of others; difficulties which had, in his opinion, been underrated.

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The author then proceeded to point out in detail what he conceived to be the history of some of the errors that had been fallen into. Thus, until lately, the descriptions given by various geologists of the rock called green sand were supposed to be applied to one bed only, whereas, in fact, there are two beds distinct from each other, the undercliff of the Isle of Wight, and the rock of Folkstone, each of which had received this denomi nation. Also in the groups which it had been found necessary to form, they had not agreed with each other as to the individual beds enclosed in one group. Thus, some had formed a group (which they called the ferruginous sand) of the sands above and below the weald clay; while others had attached the name of ferruginous sand to those below the weald clay only. He had also reason to fear, that an error had been committed in not identifying the beds which are called the ferruginous sand, on the west of the chalk, as the Carstone, Wobourn sand, and: the Faringdon bed, with the beds in the wealds of Kent and Sussex to which the name of green sand had been given.

The following is the table of equivalent beds above alluded to:

Nov. 19.-A paper was read, "On the Purbeck and Portland Beds;" by T. Webster, Esq. Sec. G. S.

The author observed, that the great general features of the geology of the Isle of Purbeck had been already traced out by him in his letters to Sir Henry Englefield. He now confined himself to some details respecting the series of limestone beds in the Isle of Purbeck, and to those in the Isle of Portland.

He then proceeded to give a description of the strata from which the well known Purbeck stone used in London, for side pavements, &c. is derived. This stone is composed almost entirely of fragments of shells. The Purbeck marble contains chiefly univalves in a compact limestone, and these in general are smaller than the univalves in the Petworth marble, both having been supposed to belong to freshwater shells; but the author possessing specimens that contain a mixture of marine with freshwater shells, he cannot consider this as a decided freshwater formation, a term that, in his opinion, ought to be restricted to those beds supposed to have been formed in lakes only. The common Purbeck stone appears to consist of fragments of small bivalves, of which the origin is doubtful..

Mr. Webster then gave a detailed account of the quarries in the Isle of Portland, which furnish the Portland stone much

used in our public buildings. The Isle of Portland consists of a mass of limestone lying upon a bed of bituminous clay and limestone identical with the Kimmeridge beds. The lower and more considerable part of the limestone in the Isle of Portland above the Kimmeridge clay, is chiefly oolitic, and contains beds of chert; but the upper part consists of a yellowish calcareous stone nearly compact, which contains in it a bed of earthy lignite abounding in silicified portions of trunks of trees, about two or three feet in length, some of which are erect, and others lie flat. As far as he could ascertain, the fossil wood was nearly confined to this stratum, and is not dispersed through the oolite as had hitherto been supposed. These upper beds of the Isle of Portland he considered as belonging to the same formation as the Purbeck beds, having found some very similar in the Isle of Purbeck.

Considering the fossil shells of the Portland oolite to be marine, while those of the Purbeck limestone are chiefly freshwater, together with the great difference in the mineralogical character, the author stated his opinion that these two series of beds should be kept in separate groups in classing the English

strata.

ARTICLE XV.

SCIENTIFIC NOTICES.

CHEMISTRY.

1. Minerals produced by Heat.

It has been very often observed, that the analyses of minerals are of comparatively little value, as long as we are not capable of reproducing by composition what had been dissolved. Prof. Mitscherlich has accomplished this important object. We have been gratified by the sight of beautiful and well-defined crystals of greyish white pyroxene, which had been obtained by mixing the constituent parts indicated by analysis in the necessary proportion, and exposing this mixture to the high degree of heat of the porcelain furnaces of Sevres. By this means, Prof. Mitscherlich has succeeded in obtaining several species that occur in nature. He has likewise observed among the different kinds of slags more than forty species in a crystallized state, particularly of such minerals as are found in primitive rocks, but likewise a good many others which have not hitherto been observed. We propose giving in our next number a full statement of the further details of these most important experiments. -(Edin. Jour. of Science.)

2. Berzelius's Analysis of the Sulphato-tri-carbonate of Lead. This eminent chemist, in analyzing some specimens of this

interesting mineral, sent to him for this purpose by Dr. Brewster, obtained the following results:

In the letter with which M. Berzelius has favoured us on this subject, he remarks, that his result accords with that of Mr. Irving, of Edinburgh, who found the carbonate of lead to be 73, and the sulphate 29, giving an excess of 2.0.-(Edin. Phil. Jour. vol. vi. p. 388.) He likewise remarks, that as he had an excess of 11 of weight of the stone, it is probable that a part of the oxide of lead in it is in the form of a subsalt. "The result," he adds, "as it is, does not agree with the definite proportions; and the small quantity of the mineral did not permit me to make ulterior experiments.'

Mr. Brooke, in his analysis, makes the results agree perfectly with the definite proportions (Edin. Jour. iii. 118), viz. about 72.5 of carbonate, and 27.5 of sulphate of lead. He had no excess of weight, and did not observe either the trace of muriatic acid or of lime.-(Edin. Jour. of Science.)

MINERALOGY.

3. Localities of Scottish Minerals.

In No. 2 of the Edinburgh Journal of Science, Dr. Macculloch has given a list of localities of some Scottish minerals. Among these several of the substances which formerly belonged to the zeolite family, are incorrectly named. Under Stilbite Dr. M. includes a red mineral from Kilpatrick Hills, and a colourless or slightly tinged substance found at Strontian. These minerals differ essentially from each other in their specific characters. The first is described in Phillips's Mineralogy, under the name of Heulandite, and the second as Brewsterite.

In reference to Comptonite, Dr. M. says, "If this be a new mineral, it is the supposed stilbite of Strontian;" that is, it is not a new mineral. But if Dr. M. had ever examined Comptonite, and compared it with Brewsterite, he would have found sufficiently marked distinctions between them to have prevented his confounding them with each other; and he would also have ascertained that Comptonite differed from every other known. mineral.

Among the localities of Nadelstein, Dr. M. refers to Kilpatrick Hills, and he also includes under this species the natrolite from Staffa.

It is evident that Dr. M. has looked at this tribe of minerals