4. From this table it appears, that the length of a degree of latitude at the poles is

At lat. 45°.

At lat. 51°

At lat. 90°

68.704 English miles

69.030

69.105

69.368

So that the mean length and degree of latitude is almost exactly 69 miles andth of a mile. Of consequence, the com mon estimate of 69 miles and a half to a degree is very erro

neous.

V. Protoxide of Copper.

About two years ago, I received from Mr. Mushet, of the Mint, part of a mass of copper, which had been for a considerable time exposed to heat in one of the melting furnaces at the Mint, of which he has the superintendence. The copper was changed into a red, granular, brittle mass, very similar in appearance to red copper ore. Grains of copper were interspersed through it in very small quantity. On reducing a portion of the specimen to powder, and pouring muriatic acid over it in a retort, I very speedily obtained a dark coloured opaque solution, quite similar to what is obtained when muriatic acid is poured upon a mixture of equal weights of fine powdered copper and black oxide of copper. This solution is known to consist of protoxide of copper dissolved in muriatic acid. When dropped into water, a white powder falls, consisting of protohydrate of copper. When dropped into a solution of potash, a yellow-coloured precipitate falls, which consists of protoxide of copper. The muriatic acid solution of Mr. Mushet's specimen exhibited exactly these appearances, and proved to be a pure solution of protoxide of copper in muriatic acid. Here then we have an instance of copper converted by heat into protoxide. It is the first example of the kind which I have yet met with; and on that account deserves the particular attention of chemists. All such accidental conversions of metals into unusual oxides ought to be carefully recorded.

I made an analysis of a portion of this curious specimen, which is not, however, to be considered as rigidly exact; for a very accurate numerical statement of such a mixture does not seem to lead to any very useful consequence. I found the constituents of 100 gr. of the specimen as follows:

*

Protoxide of copper

Protoxide of iron.

...

Silica (not quite free from iron and copper)

The mass of copper, above-mentioned, was obtained from the bottom of a furnace used for the melting of copper. The bottom of the furnace is from 9 to 12 inches thick,

formed with a round grained sand, such as glass grinders use. This mass of sand vitrifies, and becomes extremely hard, but porous; so that in the melting of copper, grains of the metal will insert themselves. The great proportion, however, in the mass, exists in a state of oxide; and by the continued use of the furnace, the greater proportion of the sand will be regularly converted into a red coloured copper ore. In the instance in question, the mass of sand converted into this red coloured ore exceeded six inches. R.M.

VI. Fall of Stones from the Atmosphere.

Among the very minute historical details of the falls of stony bodies from the atmosphere, from the earliest ages down to our own time, which have been successively published by Dr. Chladni, I do not find the following. The attention of meteorologists has been drawn to it by Sig. Domenico Paoli, in a letter published in Brugnatelli's Journal for July and August, 1818. The passage quoted is taken from the fifth chapter of the first book of a work published by Camillo Leonardi, in the year 1502. The title of the book is Speculum Lapidum. Leonardi was an inhabitant of Pesaro, in Italy, where his book was published. The passage is as follows:

"Et non solum in locis his dictis lapides generantur, verum etiam et in aëre, sicut habetur a philosophis, et maxime ab illo summo philosopho, ac nostris temporibus monarca, preceptore meo Domino Gaetano de Fienis, in comento metaurorum, in fine secundi tractatus libri tertii, qui dicit: Lapides generari possunt in aëre, cum exhalatio habet partes grossas terreas admixtas cum humiditate grossa viscosa. Et resolutis partibus magis subtilibus, et terrestribus condensatis a calido, fit lapis, qui ratione suæ gravitatis ad terram descendit. Nostris temporibus, in partibus Lombardiæ lapis magnæ quantitatis ex nubibus cecidit."

VII. Blue Glass from Iron.

It is pretty well known that the ancients were acquainted with a method of giving a fine blue colour to glass by means of iron. This method has been lost, probably because cobalt, the tinging substance used by the moderns, is much easier and much more certain of answering the object intended. Iron, however, if we are to judge from ultramarine, which owes its blue colour to iron, is capable of communicating a more beautiful colour to glass than cobalt; besides, cobalt is a very scarce metal, and sells at a high price; while iron is the most abundant and the cheapest of all known metals. On these accounts, it would be an object of considerable interest to painters, glass makers, and potters, the ancient art could be again recovered. M. Pagot Descharmes has made a number of trials, and has made known the results which he obtained in a paper published in the Journal de Physique, for July, 1818. From the imperfect experiments which he

if

describes in this paper, I am tempted to suspect that the chloride of iron is the substance possessed of this desirable property. Probably successful results might be obtained by adding chloride of iron to glass already in fusion. It would be an object worth the while of our Staffordshire potters to try the properties of chloride of iron and some other metallic chlorides as paints, either mixed with glass in the proportions that suited best, or perhaps mixed with their common enamels. There is every reason to expect that these chlorides would communicate colours different from the oxides of the same metals. If colours could be made from them for the use of the painters by uniting them with silica, as is the case with ultramarine, such colours would be much more valuable than those at present in use; because they would not be liable to undergo alterations from the action of the atmosphere, or the light of the sun. Our painters at present make use of colours possessed of so little permanency that the picture is scarcely calculated to outlive the artist.

VIII. Fusion of Platinum.

It is said that M. Prechtel, Director of the Polytechnical Institute at Vienna, has succeeded in fusing platinum by means of a very violent heat in very refractory crucibles. The greatest degree of heat which he has produced may be estimated at 180° Wedgewood. When platinum is thus fused, its specific gravity is reduced to 174. It may be scratched by a knife. It may be readily beat out under the blows of the hammer, and may be easily divided by the saw, like copper. When heated to redness and struck with a hammer, it scales off, and exhibits a granular fracture, similar to that of cast-iron. This leads to the opinion that the platinum crystallizes during its solidification. Crude platinum does not fuse at so low a heat as pure platinum.-(Gilbert's Annalen, Jan. 1818.)

IX. Formation of the Vegetable Epidermis.

Grew and Malpighi were of opinion that the epidermis of plants is merely a scurf formed upon the parenchyma of the bark by the action of the air. Mirbel has lately supported the same doctrine, and endeavoured to obviate the objections that naturally rise in one's mind when such an opinion is advanced. But Mr. Keith has shown that some of the most formidable objections of all have not been noticed by him. If the vegetable epidermis were merely the result of the action of the air upon the parenchyma, it would follow that the epidermis would never be formed till the part were actually exposed to the action of the air. But this is not the case. If we strip a rose bud, or any other flower bud of its covering, we shall find that every petal is covered with just as perfect an epidermis as those parts of the plant which have been exposed to the air. When the epidermis of the leaves or petals is rubbed off, it is never renewed. When the epidermis of the stems of woody plants is rubbed off, it is

renewed more speedily and more perfectly when the part is covered up from the action of the air than when it is exposed to that action. These facts, stated by Mr. Keith, seem to leave no doubt that the use of the epidermis in plants is the very same as in animals : that it is formed for the express purpose of protecting the parts below it, and that the analogy between the animal and vegetable epidermis is complete.-(Linnæan Trans. xii. 6.)

X. Method of procuring Meconic Acid.

The infusion of opium, from which the morphia had been precipitated by means of ammonia, was evaporated to the consistence of a syrup, and left in a state of rest; but no crystals would form in it.* It was then diluted with 16 ounces of water, and mixed with one ounce of caustic ammonia. As no precipitate appeared after the interval of an hour, the liquid was heated to drive off the excess of ammonia. When heated to the temperature of 122°, it became muddy, and 15 gr. of impure morphia were precipitated.

The liquid being freed from this precipitate and from the excess of ammonia, muriate of barytes was poured into it as long as any precipitate fell. The precipitate, being collected and dried, weighed seven drams, and was Sertürner's meconate of barytes. To obtain the meconic acid from this salt, M. Choulant triturated it in a mortar, with its own weight of glassy boracic acid. This mixture being put into a small glass flask, which was surrounded with sand in a sand pot in the usual manner, and the heat being gradually raised, the meconic acid sublimed in the state of fine white scales, or plates.

XI. Properties of Meconic Acid.

It has a strong sour taste, which leaves behind it an impression of bitterness.

It dissolves readily in water, alcohol, and ether.

It reddens the greater number of vegetable blues, and changes the solutions of iron to a cherry-red colour. When these solutions are heated, the iron is precipitated in the state of protoxide. The meconiates, examined by Choulant, are the following: (1.) Meconiate of Potash.-It crystallizes in four-sided tables, is soluble in twice its weight of water, and is composed of

It is destroyed by heat.

(2.) Meconiate of Soda.-Crystallizes in soft prisms.

Soluble

in five times its weight of water. Seems to effloresce. Decom

posed by heat. Its constituents are,

* See the notices on Morphia in the last Number, p. 153.

(3.) Meconiate of Ammonia.-Crystallizes in star-form needles, which, when sublimed, lose their water of crystallization, and assume the shape of scales. The crystals are soluble in 1 their weight of water, and are composed of

If two parts of sal ammoniac be triturated with three parts of meconiate of barytes, and heat be applied to the mixture, meconiate of ammonia is sublimed, and muriate of barytes remains. (4.) Meconiate of Lime.-Crystallizes in prisms. Soluble in eight times its weight of water. Its constituents are,

Choulant not having succeeded in obtaining meconiate of barytes in crystals, did not attempt to analyze it.

XII. On the Equivalent Number for Meconic Acid.

The numbers annexed to the analyses of Choulant, represent the equivalent numbers for the bases and meconic acid in each analysis. We see from them that the results obtained by this chemist are far from correct; for the equivalent number for meconic acid varies in each analysis. These numbers are as follows:

The mean deduced from these four salts gives us 2-714 for the weight of an atom of meconic acid. The number 275, therefore, may be considered as an approximation; but probably not a very near one. 2.75 represents the weight of an atom of carbonic acid. But it would be premature to speculate on this subject till we are in possession of more accurate analyses of the meconiates.