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WITH PREFACE AND ADDITIONAL Chapter, BRINGING THE With Two Chapters on the Future Wheat Supply of the IN the course of recent bacteriological work it was found necessary to estimate small quantities of phenol, or allied bodies, in presence of comparatively large quantities of organic matter. It is then cooled, and when rendered alkaline with concentrated ammonia, is matched against a standard solution of phenol-sulphonic acid which has been nitrated and made alkaline in a similar manner. This method of estimation does not claim to be extremely accurate, but with care it will yield sufficiently accurate results for ordinary purposes, and is sensitive enough to estimate o'ooo1 gr. phenol. The method may be extended, and a- and ẞ-naphthols and salicylic acid may also be estimated in a similar manner. The Frankland Laboratory, The University, Manchester. IRIDOSMINE FROM THE NEW RIETFONTEIN MINES: The phenolic solutions had been subjected to bacterial action, and contained, in addition to the phenol, which was only present in very small concentrations, comparatively large quantities of peptone, and other protein bodies. On this account the usual methods for the estimation of phenol were found to be unsuitable, and it was necessary By C. BARING HORWOOD, B.Sc (Lond.), A.R.S.M., A.M.I.C.E. to devise a method of estimation to suit these unusual conditions. In the literature at the author's disposal the only methods for the estimation of phenol were : 1. The method based on the formation of the bromine compound. 2. The method based on the complete oxidation of the phenol. It was hardly to be hoped that either of these methods would give reliable estimations under the conditions required, and upon experiment this was found to be the case. It was therefore necessary to devise some method by which the organic matter could be destroyed while the phenol remained to be estimated. It occurred to the author that the well known method for the estimation of nitrates might be adapted as a method for estimating phenol. This method is based on the principle that phenol sulphonic acid is readily nitrated, and that the resulting nitro body, on being made alkaline with ammonia, is changed to ammonium picrate, the bright yellow colour of which lends itself readily to colorimetric estimation. The procedure was therefore inverted, the phenolic solution being first sulphonated by warming with concentrated sulphuric acid; the phenol sulphonic acid thus formed is then nitrated, and the solution boiled to destroy completely the organic matter present, the sulphonic acid, when nitrated, not being appreciably volatile in steam. When the organic matter has thus been destroyed, the total phenol originally present in solution is still there as nitrated phenol sulphonic acid. If the solution is now made alkaline with ammonia, the bright yellow ammonium picrate is formed. By experiment it has been found that no appreciable quantity of phenol is lost, and that the destruction of the organic matter is sufficiently complete to prevent it interfering with the yellow colour of the ammonium picrate. The actual details of the method are as follows: A suitable volume of the phenol containing liquid is taken and warmed with a few cubic centimetres of concentrated sulphuric acid to 80° or 90° C.; if this tempera ture is not exceeded or maintained for more than a minute there is no loss of phenol, while this time is fully sufficient to sulphonate the phenol completely. The next step is to nitrate it and, at the same time, to destroy the organic matter. This is conveniently performed by running in to the warm solution a volume of to per cent potassium nitrate solution sufficient to oxidise the organic matter present, while at the same time the phenol sulphonic acid will be nitrated. The whole is then warmed, and if necessary boiled, to destroy the organic matter. ITS OCCURRENCE, ANALYSIS, AND GENESIS.* (Concluded from p. 245). Genesis (continued). THE original home of the metals of the platinum group, often with some gold and chromite, is admittedly the ultra-basic and basic igneous rocks (Note 20), in which they usually occur as primary segregations formed by magmatic concentration, which as Vogt (Note 21) remarks clearly indicates their original presence in minute proportion in these rocks (Vogt, loc. cit., p. 640). Thus, the original home of the platinum metals in other parts of the world, and the minerals with which they are here associated, at once suggest that at the Rietfontein mines they are not an original constituent of the banket, but were introduced at a later date, their original source being the big basic dykes which are so much in evidence in these mines. The arguments in support of this may be summarised as follows: 1. The iridosmine, and the gold with which it is associated, is crystalline, and does not show evidence of being water worn, as one would expect it to do, if it were an original constituent of the banket. 2. It is reasonable to assume that these basic dykes contain minute traces of the metals of the platinum group. Thus Vogt (Note 21) has called attention to the original tenor in the magma of the small proportion of platinum metals which has, in recent years, been found in the segregated sulphide ores of gabbro rocks, a fact which requires the supposition that the gabbro magma originally contained them. He writes:-"Some conception of this original tenor of platinum metals may be formed from the statement that the nickeliferous pyrrhotites of Sudbury contain, according to many analyses, from 25,000 to 90,000 times as much nickel as platinum metals; while the original proportion of nickel in the gabbro magma may be set down as about o'05 per cent. Hence on the (somewhat arbitrary) assumption that the platinum metals were concentrated from the magma to the same extent as the nickel, the magma contained, roughly, o 000001 per cent of these metals. This figure, of course, has no pretension to accuracy, but we have at least learned that even the platinum metals are among the normal constituents of the basic eruptive rocks." At the Rietfontein gold mines it took about six months to collect about 910 grains of the heavy concentrates, during which time 102,800 tons of ore were crushed, and over 52,500 ounces of fine gold were recovered. From these figures it would seem that the Rietfontein pay reefs contain about 27,500 times as much gold as metals of the platinum group (Note 22). The neighbouring • Transactions of the Geological Society of South Africa, 1912, xv, 52. |