a long continued gentle heat. The whole was now very carefully neutralized with a weak solution of potash so as just to avoid the reprecipitation of the salt: nitrate of lead from fresh dissolved crystals was carefully added, avoiding excess, which was shewn by the clear liquor above the white precipitate undergoing no change from sulphate of soda nor hydriodic acid. The precipitate boiled, well washed and dried was after a red heat = 31.23 grains, equi-" valent to 6.246 of phosphoric acid. A solution of caustic potash was added in excess and boiled upon the black precipitate formed; this when separated and dried at a heat below redness weighed 18.1 grains, and was Copper in the same state of oxidation as in the mineral*. Now this loss would appear considerable, if we do not take into account the impossibility of having driven off all the combined water, for reasons above stated. If we consider that loss to be water, the result will stand thus, Phosphoric acid.... 6.246 = 21.687 Per-oxide of copper 18.1 = 62.847 per cent. 4.454 15.454) * The analysis was also accomplished in another manner, by adding hydrate of ammonia in such excess as to redissolve the precipitate at first formed. The phosphoric acid was then precipitated by cautiously adding nitrate of barytes, and after the liquor had been rendered acidulous by sulphuric acid, the copper was separated by a plate of iron. The method described in the text has, however, practical advantages. Now it is fair, at least, to compare all theory with experimental results; if we consider the mineral as composed of 1 atom of phosphoric acid, 1 atom of per-oxide of copper, and 2 atoms of water, the quantities per cent. will stand as below; and by the side I have placed the experimental result for comparison. It will be seen that the difference is in no case equal to unity except in the water*. If we were to represent the constitution of this mineral by the symbols of Berzelius, which being derived from the Latin are more general than the English initials of Thomson, but adopting the opinion of the latter with regard to the constitution of phosphoric acid, Its chemical sign would be CuP+2 A q. Its mineralogical There can be no doubt of Chenevix's artificial phosphate being a bi-phosphate, as stated by Thomson +; and it is rather singular that a neutral combination which has not hitherto been formed in the laboratory of the Chemist, should be the very substance formed by a natural process in the earth. * Throughout these calculations I have made use of the atomic weights recently laid down by Thomson, because in some trials of verification I found them to accord best with experiment. + Thomson's System of Chemistry, Vol. II. p. 607. 5th edit. XIII. Upon the regular CRYSTALLIZATION of Water, and upon the form of its primary Crystals; as they were naturally developed in Cambridge, January 3, 1821, and were seen during the two following days. BY EDWARD DANIEL CLARKE, LL. D. LATE FELLOW AND TUTOR OF JESUS COLLEGE; PROFESSOR OF MINERALOGY &c. &c. [Read March 5, 1821.] THE frost which took place towards the end of the last and beginning of the present year (1821), was particularly favourable for the exhibition of a phænomenon Naturalists have been often anxious to witness; namely, the perfect Crystallization of Water. This happened in Cambridge, under circumstances worthy of notice; because it exposed to view the primary form which Hydrogen oxide assumes in the solid state; and because it is a commonly received opinion, although erroneous, that to observe any appearance of this nature we must visit distant regions, liable to a much greater diminution of temperature than any part of the Island of Great Britain; such as might be found in Latitudes where Water is constantly maintained in the solid state. That the compound of which Water consists, does obey the same laws to which the particles of all other oxides, and of all other bodies, are liable, when they pass from the fluid to the solid state, is no new discovery-it is even older than the researches of those Philosophers to whom the first dawnings of the Science of Crystallography have been usually ascribed. It must have attracted the regard of scientific men as long as the ramified congelations at the surface of glass windows, during the time of a frost, have been offered to their view: the remarkable circumstance of the arrangement of the spiculæ, intersecting each other under constant angles of 120° and 60° would surely not have escaped their observation; indeed, we can prove that it did not; for the same disposition of particles, being exhibited with a striking character of symmetry in Snow, (which sometimes falls in star-like forms, with six radii, bisecting the angles of a regular hexagon,) was noticed, before the Age of Newton, by Descartes who attempted to explain the phænomenon. Mairan, afterwards in his dissertation upon Ice, compared the appearance with that of the Striæ visible upon the surfaces of some of the crystallized sulphurets of Iron; and in connecting it with a result of the laws to which the structure of all Crystals is subjected by that force which disposes the particles of bodies, when in the vicinity of contact, to combine together under geometrical forms, Mairan was not far from the truth. The same subject early excited the attention of those celebrated French Chemists, who, towards the conclusion of the last Century, were engaged in publishing an account of their transactions. Monge, afterwards President of the National Institute of Paris, in the Météréological Mémoire, with which the fifth Volume of the "Annales de Chimie" commences, alludes to this beautiful effect of crystallization in Snow; and he gives the first satisfactory explanation of the phænomenon; illustrating what passes in the vast Laboratory of Nature, by reference to an easy experiment |