Experiments made by Professor Miers and Miss F. Isaac have shown how, by measurements of the refractive index, it is possible to determine for a supersaturated solution the temperature at which it passes from the metastable condition, in which it can only crystallize by inoculation with a crystal of the salt (or of a substance isomorphous with it), to the labile condition, in which it may (and often does) crystallize spontaneously. In a diagram in which concentrations are taken as ordinates and temperatures a abscissae the solubility curve represents the limit between the unsaturated and the metastable state; and the limit between the metastable and the labile state is represented by a similar curve, to which they have given the name ‘Supersolubility curve’.

For many years past Mr. R. H. Solly has been accustomed to spend each succeeding summer in the quest of mineral specimens in the neighbourhood of the village of Binn, Switzerland, particularly of those occurring in the white crystalline dolomite of the Lengenbach quarry, and his patient energy has been rewarded by the discovery, not only of material which has thrown fresh light on previously known minerals, but also of specimens which on examination proved to represent species new to science. Especially important was the discovery in 1903 of small, and often minute, blood-red crystals which differed both in colour and in streak from realgar, a common mineral in the quarry.

In a paper communicated to this Society in March, 1903, it was shown that antimonite is fairly transparent to radiations of long wave-length and that its behaviour between crossed nicols is consistent with orthorhombic symmetry. At the same time it was pointed out that it would be of interest to determine the wave-lengths of the radiations transmitted and the principal indices of refraction of antimonlte for these radiations. On undertaking this investigation it was soon found that antimonite was quite sufficiently transparent to the rays at the extreme red end of the visible spectrum to enable visual observations to, be made, and in a verbal communication to the Society on March 22, 1904, it was stated that the indices of refraction for red light were 4.129 for rays vibrating parallel to the axis Z and 3.873 for rays vibrating parallel to the axis X.

During the investigation of a zeolite it became necessary to separate small quantities of zeolitic material from a mixture of calcite and other heavier minerals; this could be done most easily by using a liquid of such density that the zeolite just floated, while all the other minerals sank to the bottom. A solution of potassium-mercuric iodide could not be used, as this reacts chemically with zeolites and alters their composition ; acetylene tetrabromide diluted with benzene was therefore chosen, and in consequence the apparatus had to be made entirely of glass. Certain dittlculties were found in using the ordinary form of glass separating apparatus, and to overcome these the form here described was devised.

In a previous paper the author pointed out the advantages of a goniometer possessing three graduated circles, and described an instrument of this type which had resulted from the addition of a two-circle arrangement to an ordinary reflective goniometer with a single (horizontal) circle. As was remarked in that paper, the adapted instrument has unavoidably the disadvantage that measurements can be made through little more than a right angle in any particular zone, with the single exception of the zone of reference, without readjustment of the vertical and third circles. The zone may, indeed, be completed by measuring from the diametrically opposite pole in the zone of reference; but difficulties occasionally arise in practice, and it is convenient to be able to measure through at least two right angles round the free end of the crystal by rotation of the horizontal circle only.

A preliminary notice of this new mineral, named in honour of Dr. Arthur Hutchinson, Demonstrator of Mineralogy in the University of Cambridge, was read before the Cambridge Philosophical Society in October, 1903. The material was first found, in the white crystalline dolomite of the Lengenbach quarry, during my visit to the Binnenthal in the summer of 1903. More material was received in November of the same year, and a further supply was obtained in 1904.

During the last twelve years I have communicated to this Society, often in collaboration with Dr. G. T. Prior, several papers descriptive of Bolivian minerals. These papers have dealt primarily with the species augelite, andorite, argyrodite, stannite, and chaleostibite, though many others have been examined and in some cases incidentally mentioned. The latter, as being of lesser general interest, or as not having led to sufficiently important results for separate publication, are now collected together in the present notes.

As has been mentioned in the preceding communication, a supersaturated solution, which is cooling or evaporating, passes successively into the metastable condition, in which an introduced crystal can grow in it, and then into the labile condition, in which it may crystallize spontaneously. The transition is indicated by a sudden change in the refractive index of the solution. It seems possible that in these two distinct states of the solution there may be a difference in the mode of growth of the crystals. In the following experiments an attempt was made to find evidence of such a difference by the examination of thin drops of solution crystallizing under the microscope: and potash-alum was found to be a convenient substance for the purpose.

Lengenbachite is one of the interesting minerals which occur in the dolomite of the Binnenthal, and we owe our knowledge of it, as of many other new species, to the careful investigations conducted in recent years by Mr. R. H. Solly at that remarkable locality. The crystallographic and physical characters, so far as they have proved capable of determination, have been already described by Mr. Solly in the pages of this Magazine (vol. xiv, p. 78). The material which he kindly placed in my hands for chemical examination consisted of cleavage-plates, exhibiting brilliant metallic lustre, and of foliated aggregates of thin greyish-black crystals. Some of the crystals were partially covered with a thin, white incrustation readily removed by boiling dilute hydrochloric acid, a reagent which appeared to be without action on the lengenbachite.

The first form of refractometer, in which a reference-scale was substituted for the rotational parts and graduated circles of the more complex instruments, was designed in 1885 by Professor E. Bertrand who at the same time was the first to suggest the employment of a hemisphere of dense glass in place of the prism and cylinder previously used. The original instrument and others on the same principle which have hitherto been constructed do not give satisfactory results, because no attempt has been made to compensate for the curvature of the focal surface of the hemisphere, and the determinations obtained are, therefore, far from trustworthy. In the refractometer described in this paper a corrective lens is placed in the path of the rays emerging from the hemisphere, and the field thus produced is rendered very nearly plane.

Flexible mineral fibres appear to have been well known to the Greeks, who spun them into thread, which they wove into cloth or employed as wicks for lamps.

Pausanias, who lived in the second century of the present era, tells us that Kallimachos made for the statue of Minerva in the Acropolis at Athens a lamp of gold, the wick of which was of ‘karpasiau flax’, which he states is the only flax inconsumable by fire. Some have interpreted the words ‘karpasian flax’,——as meaning mineral flax from the Karpasos, the north-eastern promontory of Cyprus, but apart from the fact that there is no record of the occurrence of asbestiform minerals in that locality, it seems clear that the word is derived from (feminine in the singular, but neuter in the plural ), which properly signifies cotton, being identical with the Sanskrit , though it has been used for a fine variety of flax produced in Spain, as well as for other European plants.

The formula 2PbS. Sb2S3, given for jamesonite in all the textbooks, does not belong to jamesonite at all, but to the ‘Federerz’ (‘feather-ore’) from Wolfsherg in the Harz analysed by H. Rose in 1829, and for which the mineralogical names wolfsberglte (Huot, 1841) and plumosite (Haidinger, 1845) have been proposed. Rose's formula for the cleavable jamesonite from Cornwall was 3PbS. 2Sb2S3. In 1860 Rammelsberg united these, together with heteromorphite, under the name jamesonite and with the formula 2PbS. Sb2S3 a : this has since been followed in the textbooks, but, as will be pointed out below, it is very probable that there are here three distinct mineral species.

One of the peculiarities of Bolivian tin-ores is the frequent occurrence of cindery and cellular masses of cassiterite, which is presumably of secondary origin. But, apart from impressions of quartz crystals, definite crystal-forms are rarely shown by this pseudomorphous cassiterite.

The pseudomorphs to be now described are from the Tres Cruces district, and were collected by my son, Mr. A. W. Pearce. The crystallographic determinations have been made by Mr. L. J. Spencer, and the specimens examined by him have been presented to the British Museum. The material consists of cavernous masses of dark brown, finely crystalline and granular cassiterite, associated with which is a pale yellow, ochreous substance.

Anatase.—Some very brilliant and highly modified crystals of a light brown colour were obtained from the Ofenhorn in 1908. The largest crystal measures nearly an inch across. The. form {313} is largely developed; other forms present are {100}, {110}, {111}, {331}, {221}, {223}, {835}, {112}, {118}, {117},and also a new {h k l} plane close to (110) and (221), which is probably (24.14.7). These crystals resemble Seligmann's fig. 3.

In 1902 some much smaller, dark brown crystals of a different habit, with the form {117} largely developed, were obtained from another part of the Ofenhorn. They resemble Klein's fig. 3. Three new forms were observed, namely {553}, {35.8.5}, and {40.3.5}.