and came to England, entering the house of the late Andrew Ross, the founder of the well-known optician's business bearing his name. Mr. Dallmeyer's attention was at first devoted principally to the construction of astronomical telescopes, for which, in conjunction with Mr. Ross, he computed a large number of formulæ. At his death, Mr. Ross bequeathed to Mr. Dallmeyer the bulk of his optical appliances for the manufacture of telescopes. About this date (1855) photography began to be popularized by the general adoption of the collodion process. Mr. Dallmeyer quickly discovered that the photographic lenses then in use stood in great need of improvement in every direction. In rapid succession he produced lenses for landscape and portrait photography, and it is greatly owing to his efforts that English lenses now rank second to none. He was specially commissioned to provide several of the telescopes and photographic appliances used by the different Government expeditions for the observation of the recent transit of Venus, and his telescope object-glasses are in high repute among the leading astronomers. Mr. Dallmeyer died at the age of 53. One more duty falls upon me, and it is a very pleasurable one. I have to thank the Fellows of the Society for the consideration they have shown me during my three years of office, and for the manner in which they have borne with my shortcomings. In taking leave of you as your retiring President I do most sincerely congratulate you on the accession of Mr. Dallinger to the presidential chair, a position for which his great scientific reputation so thoroughly recommends him. Ser. 2.-VOL. IV. 0 V.-On the Mineral Cyprusite. By JULIEN DEBY, C.E., F.R.M.S. (Read 14th November, 1883.) IN November 1881, Dr. Paul Reinsch, through Professor Stokes, communicated to the Royal Society a note on a mineral to which he gave the name of Cyprusite, of which he had brought back to Erlangen a small specimen on his return from Cyprus. Having myself had the opportunity of visiting the same region of country during the present summer, I took advantage of it to collect numerous specimens of this substance, from many different localities. Believing that further observations relating to this cyprusite may prove of interest to petrological microscopists and others, I have drawn up a short note summing up the further history of this curious natural product, the result of my own investigations. The cyprusite is found in the shape of rocks, forming several bold superficial parallel outcrops of rather irregular longitudinal outline, running in a direction north-west to south-east in the district of Chrysophou, in the north-west portion of the island of Cyprus, and mostly distributed over the mountainous territory comprised between the villages of Poli, Lisso, and Kynussa. These outcrops extend in some cases several hundred yards in length, with a width oscillating irregularly between 30 to 100 yards. Their colour varies from a pale dirty yellow to a bright cinnabar red, with all intermediate tints. The texture of the rock varies from a quite soft friable consistency, falling to dust between the fingers, to a quite hard and compact rock. The former or softer variety is the most abundant. A careful geological examination shows that the cyprusite is imbedded in plutonic rocks, melaphyres, and wakes, containing occasionally zeolites, it occupying wide crevices in these eruptive rocks, which latter have forced their way in vast masses through the stratified tertiary fossiliferous limestones of the country. The present height above the sea of the cyprusite deposits varies from 350 to 1200 feet, the distance of the same to the north coast of the island in a straight line varying from three to six miles. The principal deposits are situated on the right bank of the Ballahusa river, and below the village of Kynussa. Having noticed that wherever cyprusite outcrops were to be seen traces of ancient mining and heaps of old slags were also to be discovered in the vicinity, and that the old workings penetrated in many places into the hill-sides below the yellow masses, I came to the conclusion that the cyprusite knobs and bluffs formed the outcrop ("gossan," as Cornish miners would call it) of the copper lodes so celebrated in the times of remote antiquity. A further investigation has led me to the belief that, at a certain depth, the cyprusite is replaced by iron pyrites, and that lower down still these pyrites become cupreous, and that these constituted a portion of the mineral which was worked by the Phoenicians, Greeks, and Romans in the island of Cyprus. I observed in several places below the cyprusite the efflorescences mentioned by Dr. Reinsch; their composition is as follows: This mineral had a whitish, slightly greenish tinge and semicrystalline structure, and looked exactly like weathered sulphate of iron. It consists, however, essentially of sulphate of alumina (nearly 2 Al, 03.5 SO3 + 25 H2 O) coloured by copper. The cyprusite was submitted for complete analysis to my friend Henry Fulton, Esq., the late well-known and able chemist to the Rio Tinto Company, now of Aguilas, Spain, to whose kindness I am indebted for the greater part of the chemical determinations in the present communication. A first experiment consisted in simply drying the mineral to from 100 to 115 degrees Centigrade, when slight vapours which coloured litmus blue were given off. Another portion was next submitted to a red heat in a platinum crucible for six hours, until the fumes ceased to colour litmus paper, when it was found by analysis that 17 19 per cent. of sulphuric acid had been given off. At the same time the colour had passed from yellow through bright red to a dark purple. The average of several carefully made analyses of the yellow or typical and most abundant variety of cyprusite, after separation of the insoluble portion, which, as we shall see, does not enter into the chemical composition of the mineral, was found to be: The mineral is thus seen to constitute a normal sulphate of alumina with anhydrous ferric tribasic sulphate, the whole having the formula, Al, 03. 3 SO3 + 18 H2O + 8 (Fe2 03. SO3), the theoretical composition of which would be as follows: differing from the result of Dr. Reinsch's essay, as published by him in the 'Proceedings of the Royal Society' for 1881, No. 217. The most interesting facts connected with the cyprusite are, however, revealed by a careful microscopic examination of the mineral. It is then found to consist of a loose to compact aggregate of very minute, translucent, very slightly coloured crystals, the microscopic "projection" of which is generally more or less regularly hexagonal. These crystals vary in diameter from 1/120 to 1/300 of a millimetre 8.30 μ to 3·32 μ = 0.00032 of an inch to 0.00013 of an inch. These are entirely soluble in hydrochloric acid, but insoluble in water. Calcining converts these crystals into an opaque substance, which generally retains the previous outline. Crystals are frequently found irregularly formed, as also occasionally compound or twin-crystals. Under the polariscope the micro-crystals, if examined dry or immersed in water, would, by a superficial examination, be taken for isometric, an appearance which is due to the hexagonal disks, all presenting this same face towards the optical axis of the instrument, but if mounted in thick balsam so as to lie in various positions to the observer, they are found, small as they are, to be beautifully anisotropic, the hexagonal sections alone remaining obscure under the crossed Nicols, so that the crystalline system may be safely laid down as rhombohedral or hexagonal. This determination is further supported by the fact that some of the larger crystals seem to present apical modifications which are multiples of three. It will be remembered that the ordinary alums, as also copperas, crystallize in the monometric system, so that cyprusite seems to constitute a really good and distinct mineral species. I may add that cyprusite is insoluble in water, and that analysis has failed to detect in it either lime or magnesia. The specific gravity is 1.8. Completely immersed in this bed of minute crystals of cyprusite are to be found scattered numerous silicious organic remains (non-polarizing) to the extent, on an average, of about 16 90 per cent. of the whole bulk, along with a very few small grains of quartz sand, which last are readily distinguishable under the micro-polariscope. The Microscope shows that these silicious organic remains, invisible to the naked eye, consist of the skeletons of marine polycistins (Radiolaria) in a tolerable state of preservation, along with many smaller débris of the same, as also of a few sponge spicules, but I could discover no diatoms among them. The cyprusite polycistins belong principally to the group comprising the Heliosphæridæ, but a curious elongate conical form of a Polycyrtida is not uncommon in the deposit as well as representatives of some other families. The insoluble residue of the mineral after treatment by acids consists almost entirely of these organic remains. Ehrenberg's and Haeckel's works not being at my disposal at my present residence in Spain, I cannot determine the species nor even the genera of these Radiolaria, nor can I establish if these forms are still living in the present surrounding seas. I must, in consequence, leave this work for others better situated, and to whom I will be glad to communicate the necessary material on application. One thing is certain, namely, that at one time or another, the cyprusite beds must have existed under the level of the sea. The origin of the cyprusite is a subject of some difficulty, and lies, to a certain extent, within the realms of scientific speculation. Its chemical production, as well as its geological genesis, may, however, I believe, be explained theoretically by reference to the following considerations: It is well known that a solution of a ferrous sulphate, exposed to the air, undergoes oxidation. According to F. Muck,* in the earlier stages of the oxidation, the solution contains normal ferric sulphate Fe, 03.3 SO3, and even free sulphuric acid, but ultimately the basic salt Fe, 03.2 SO, distinguished by its deep brown colour. At the same time the deposit becomes progressively richer in acid, without, however, attaining the composition 2 Fe2 03. 3 SO, assigned to it by Wittstein.t The products of the oxidation vary with the continually changing composition of the solution, and cannot therefore be reduced to any simple expression. As a rule, ferric sulphates, occurring as natural products, are partly precipitates of this kind, and partly dried up mother-liquors. The tribasic ferric sulphate Fe, 03. SO3 Fe2(SO4)3 2 Fe2 03 is produced artificially as a reddish yellow powder, containing about 3 at. water, by dissolving the basic double salts of potassic sulphate and sesquibasic ferric sulphate in water, and heating the solution (Soubeiran). If potash or soda be added to a concentrated solution of ferric sulphate till the precipitate no longer redissolves, the filtered solu * Journ. Pr. Chem., xcix. p. 103; Jahresb. 1866, p. 241. |