wholly of a siliceous nature, a deposit of natron should have taken place, so remarkable as this noticed by Dr. Wavell within the interior of the tower, where the decomposition of the stone has proceeded to such a length, as to have given rise to the cavities which he has described. In a second letter which he has addressed to me upon this subject, he says, "The church is large and antient; the tower, a very fine one, is a sea-mark; and, in a direct line, is not more than half a mile from the sea. I observed no appearance of decay in the stones of the exterior of the tower; it seemed wholly confined to those of the interior. How have these stones been thus acted upon; and whence originates the salt with which their cavities are laden? Many from their honey-combed appearance seem to have resolved themselves into this salt."

The origin of the salt and its chemical constituents have been already sufficiently explained. The only doubt, as to its formation, may possibly attach to the source of the carbonic acid which has combined with the soda; i. e. whether it were derived from the small quantity of the carbonate of lime which the mortar contains, or has resulted from the action of atmospheric air. There is something also paradoxical in the nature of the action which has produced such a remarkable instance of decomposition in the stones of the tower; and this only upon the interior walls. Further observations made upon the spot, may perhaps clear up these points. For the present, having already trespassed long enough upon the attention of the Society, any additional remarks upon this subject may be reserved for future consideration.

EDWARD DANIEL CLARKE.

Cambridge,

Nov. 15, 1820.

C c

XII.

Analysis of a native Phosphate of Copper from the Rhine.

By FRANCIS LUNN, B.A. F.R.S.

OF ST. JOHN'S COLLEGE, CAMBRIDGE.

[Read March 5, 1821].

AMONG the Analyses of Klaproth* is one of a Phosphate of Copper from the Firneberg near Rheinbreitenbach on the Rhine: the mineral had long been mistaken for Malachite from its external resemblance. The German chemist obtained as his result

Oxide of Copper. ....68.13

Phosphoric Acid......30.95.

And this Analysis has been adopted by

Haüy — Brogniart —

Thomson-Jameson-Phillips, and in short copied into every Mineralogical classification which has appeared. Its accuracy has been doubted †, it is true: for water to the amount of 15 per cent. is overlooked; but the rarity of the substance has prevented chemists from subjecting it to a new examination.

Having lately received some copper ores brought from a mine at Erpel near the town of Bonn‡, among these were specimens

* Beiträge zur Chemiscen, III. 206.

+ L'Analyse de M. Klaproth n'indique pas que l'eau entre dans la composition de ce phosphate, cependant il en conteient une quantité assez considérable; &c. &c. Cette circonstance jette doute sur l'exactitude de l'analyse de Klaproth; elle mérite bien d'etre répétée Berzelius. Nov. Syst. p. 246. Paris 1819.

For these very fine specimens, I am indebted to George Samuel Kett, Esq. Brooke House, Norfolk.

204

Mr. LUNN on Native Phosphate of Copper.

of the mineral in question. In mineralogical characters it agrees with the description of Klaproth.

In colour it is emerald green, but shaded and streaked with black green, and to this colour the external natural surface approaches; it is opake, its powder is verdegris green, it has a diverging striated texture and a silky lustre, the specific gravity of one very pure fragment was 4.2, its hardness is rather beyond that of Malachite. It was in no instance crystallized, although on the external surface of some specimens an imperfect tendency to crystallization was perceptible. It occurs massive in a white opake quartz rock, in places slightly tinged by oxide of iron; and it is soluble in nitric acid. By exposure to a red heat in a close crucible it becomes of a dark olive green colour, and the powder increases considerably in bulk. Before the blow-pipe on charcoal it readily fuses into a reddish black slag adhering to the charcoal, and by the addition of carbonate of soda it is reduced to a bead of pure copper.

In some specimens it is accompanied by crystals of phosphate of lead.

Although the elements of this mineral are not numerous, yet wherever phosphoric acid enters, considerable caution is necessary to ensure correct analytical results: nothing can more fully prove this than the discordancies between the results obtained by two of the most expert analysts, Professors Thomson and Berzelius, and yet both have exerted their utmost skill on this very subject.

It was necessary to make several previous trials to find out a precipitant which might be depended upon; or rather, to find out the mode of using any of the old ones which would produce accordant results. These trials were made upon anhydrous phosphate of soda by barytes, lime, and the salts of lead. I need not repeat a tedious course of experiments, but may mention the results: the objection to the earthy salts is that unless the solution

be most strictly neutral, or even rather alkaline, a very small quantity of the phosphoric acid enters into insoluble combination; these therefore would not answer the intended purpose, because at the very point when the re-agent would be useful the original salt was itself precipitated.

To the salts of lead then we must have recourse: the muriate appears to have the preference with Berzelius*, and with this salt accordant results may be obtained; but both the saline solutions must be most strictly neutral, and the very low degree of solubility of muriate of lead after it has once been crystallized, is a considerable practical inconvenience. With the nitrate of lead I could obtain unvarying results; it is easily crystallized, and when carefully washed and redissolved is perfectly neutral and of high solubility.

In both the above methods it is advisable, to ensure accuracy, that no more of the solution of the salt of lead be added than is necessary to separate the phosphoric acid; and the precipitate must be boiled in water, by which means the combination of acid mentioned by Berzelius† may be avoided.

ANALYSIS.

A portion of the mineral free from any foreign ingredient was reduced to a fine powder; this after being dried at the temperature of 212o, was of a verdegris green colour, and weighed 28.7 grains; by subjecting it to a low red heat in a platinum crucible it became olive green, more bulky, and lost 2.15 in weight, which was water driven off; it was not adviseable to let it remain long at that heat, for it is capable of being volatilized, which appeared by some condensing on the lid of a crucible. The whole was now dissolved in dilute nitric acid, and formed a clear blue solution; from this as much water and excess of acid was driven off as possible by