analogous in character to that of argon, but differing entirely in the position of the lines. With the ordinary discharge the gas shows three lines in the red, and about five very brilliant lines in the blue; while with the jar and spark-gap these lines disappear, and are replaced by four brilliant lines in the green, intermediate in position between the two groups of argon lines, the glow in the tube changing from blue to green. Xenon appears to exist only in very minute quantity. 155 Having obtained practically pure materials, we proceeded to study the reactions when the conditions were varied by employing hot or cold and strong or weak cupric sulphate solutions. We were met with the initial difficulty that cupric sulphate solution deposits a basic salt when it is boiled: this salt we separated and found to correspond in composition and properties to the formula 4CuSO4.7Cu(OH)2. H2O. Pickering had separated a similar salt, to which he attributed the formula 6CuO.2SO3.5H2O. Owing to the deposition of this salt complicating the products, we avoided actual ebullition in our experiments. Indeed all of these gases are present only in small amount. It is, however, not possible to state with any degree of accuracy in what proportion they are present in atmospheric argon. Of neon, perhaps, we may say that the last fraction of the lightest 100 c. c. from 18 litres of atmospheric argon no longer shows the neon spectrum, and possesses the density of argon; it may be safe to conclude, therefore, that 18 litres of argon do not contain more than 50 c.c. of neon; the proportion of neon in air must therefore be about one part in 40,000. We should estimate the proportion of the heavy gases at even less. It follows from these remarks that the density of argon is not materially changed by separating from it its companions. A sample of gas, collected when about half the liquid argon or about 1o c.c. had boiled off, possessed the density 1989; the density of atmospheric argon is 1994. But, of course, we give this density of argon as only provisional (July 30, 1898); for a final determination the density must be determined after more thorough fraction-equivalents of the cuprous oxide, the copper, and the hy ation. With a density of 9'6, and a consequent atomic weight of 192, neon would follow fluorine and precede sodium in the Periodic Table; as to the other gases, further research will be required to determine what position they hold. EQUIVALENT REPLACEMENT OF METALS. By Professor FRANK CLOWES, D.Sc. (Lond.). IT has long been known that when iron is immersed in a solution of cupric sulphate metallic copper is deposited, and an amount of iron passes into solution which is exactly able to combine with the sulphate radicle liberated from the cupric sulphate. The weights of copper and of iron which combine with the same weight of sulphate radicle have been determined by carrying out the process quantitatively. These weights are chemically equivalent to one another, for they are able to combine with the same weight of the acidulous radicle. In the case just cited, the chemical change appears at ordinary temperature and with dilute cupric solution, to follow the simple course stated. But attempts to extend this direct method of ascertaining the relative equivalents of metals cease to be direct in certain cases, owing to the complicated nature of the reactions which occur. My attention was drawn to such a complication in the case of the action of magnesium on cupric sulphate solution, and the nature of the reaction was then investigated by R. M. Caven, B.Sc., and myself. Commaille (Comptes Rendus, Ixiii., p. 556), Kern (CHEM. NEWS, xxxiii., p. 236), and Vitali (Fourn. Chem. Soc., lxx., 419), had drawn attention to the facts that during the action of magnesium on cupric sulphate solution cuprous oxide was deposited with the metallic copper, and hydrogen was evolved. These facts prove that the copper equivalent of magnesium cannot be obtained by simply weighing the magnesium which passes into solution and the deposit which was formed during the process. But we proceeded to make a fuller examination of the nature of the reaction, and to show that when it was quantitatively carried out the products enabled us to calculate the equivalents of magne. sium and copper. A Paper read before the British Association (Section B), Bristol Meeting, 1898, The action is most simple when the magnesium is im mersed in a hot strong solution of cupric sulphate. Hy. drogen is briskly evolved, a chocolate-coloured deposit forms, and green flakes are produced which disappear be fore the reaction is completed. Treatment of the brown deposit with dilute hydrochloric acid yields colourless cuprous chloride solution and a small residue of metallic copper. The hydrogen evolved was collected and measured, the metallic copper was weighed directly, and the amount of cuprous oxide was determined by dissolving it in hydrochloric acid and determining the amount of cuprous chloride thus formed by titrating it with standard permanganate solution in the presence of a sufficient amount of magnesium sulphate. As a result of four experiments the average sum of the magnesium drogen amounted to o'102 grm., and the average weight of magnesium used was o'105 grm. The ratios of the weights of hydrogen, copper, and cuprous oxide produced were constant only when the conditions of the experiment were precisely similar. When the hot cupric sulphate is dilute, or when it is employed at ordinary temperature, the reaction pursues at first a similar course, but it soon becomes very considerably delayed by the formation of a green basic cupric salt, intermingled with colourless basic magnesium salt. Thus the reaction on the magnesium was usually complete in ten minutes in an excess of a hot strong solution of cupric sulphate; but in weak and cold solutions it often extended over several days, and even a week. The percentage of hydrogen, compared with that which is equivalent to the magnesium employed, was in the case of the hot solution 347; with the cold solution it was 415 with weak solution, and 30'6 with saturated solution. Various explanations have been given of the causes which lead to deposition of cuprous oxide and to evolution of hydrogen. It has been suggested that the change is due to impurity in the copper salt; this we have disproved by using a salt purified by frequent re-crystallisation, and yielding 25°23 per cent of copper (theory = 25'39); we have also proved the purity of the magnesium employed. Divers suggests that the evolution of hydrogen is due to the action of the magnesium upon free sulphuric acid, which has been formed by hydrolysis of the cupric salt. This seems to us to be an insufficient explanation of the rapidity with which hydrogen is evolved. Cold cupric sulphate solution was found to give no acid reaction with methyl-orange, although it is faintly acid to litmus paper. Yet such a solution gives an immediate evolution of hydrogen when magnesium is immersed in it, the evolution of the gas being very rapid in a hot and strong solution. After carefully studying the change, we are inclined to attribute the evolution of hydrogen in small degree to the presence of free sulphuric acid formed by hydrolysis in cold solution, and in greater degree to the same cause in hot solution. This involves the formation and separation of basic salt. This reaction, however, does not account for all the hydrogen evolved, and one of us will be prepared before long to advance a further explanation to account for this. Divers further suggests that cuprous sulphate is formed and almost immediately converted by the action of the basic cupric salt into cuprous oxide; this theory we also find to be untenable. 156 Luminosity produced by Striking Sugar. CHEMICAL NEWS, The immediate separation of cuprous oxide and evolution, when in use and afterwards, that the acid may not come of hydrogen, without formation of basic salt, which occurs at the commencement of the reaction, may be represented by the equation 2Mg+2CuSO4 + H2O=2MgSO4 + Cu2O+ H2. The action of the magnesium-copper couple has been proved to be too slow to explain the rapid escape of hy drogen, and if this were the origin of the hydrogen, its escape would not immediately follow the immersion of the magnesium. ON A CONVENIENT FORM OF DRYING TUBE * A COMMON method of drying gases is to pass them through a wash-bottle containing sulphuric acid and then through a U-tube filled with fragments of pumice moistened with the same liquid. The number of corks and connections in contact with the corks; if too much acid is poured in, the bend becomes blocked by a plug of liquid; there is no means of telling when the acid has become less efficient by dilution; nor is it easy to re-charge the tube with fresh acid. The form of drying-tube shown avoids these defects. It is at once wash-bottle and drying-tube. It has one cork and stands upright; the pumice can be well drenched with sulphuric acid, the excess draining down and filling the lower part (through which the gas bubbles) to a convenient height; dilution announces itself, and the acid is easily renewed. The shape is that of a Gay-Lussac burette with a constriction about two inches from the bottom. A piece of pumice, large enough to block the constriction is first dropped in, and the tube is filled to near the top with small fragments of pumice. In charging with acid care is taken not to wet the upper part of the tube; next day the level of the acid in the lower part of the tube is marked with a strip of gummed paper. small side tube which enters the large tube near the bottom is the inlet for gas; when the moisture absorbed The has raised the level of the acid about 2 m.m. above the mark, the acid in the lower part is poured off through the small tube, and fresh acid is poured in through the pumice. The inlet and outlet tubes are made of the same height, so that a series of similar drying tubes may readily be joined together. in this arrangement increase the chance of leakage. The U-tube must be supported in an upright position both * A Paper read before the British Association (Section B), Bristol Meeting, 1898. ON THE LUMINOSITY PRODUCED BY By JOHN BURKE, M.A. WHEN two lumps of sugar are struck a flash is produced of a somewhat bluish white colour, but the light is instantaneous, and yet at the same time spreads into the sugar itself far be. neath the struck surface. An almost continuous luminosity, however, has been produced by a hammer striking automatically the rim of a rapidly rotating wheel of sugar (obtained by cutting up a sugar-loaf into a number of discs); the wheels or discs being about an inch thick, so as to stand the violent hammering; the hammer, being of the nature of a pendulum about four feet in length, which was drawn aside by an electro-magnet and then let go. Curiously enough, if the impact is given when the wheel is stationary, so that only an impulse is given without rubbing, or if, on the other hand, the wheel is set spinning and the hammer is stationary and merely allowed to rub up against the wheel, the phenomenon is insignificantly small compared to that obtained when both rubbing and knocking take place together; that is, when the wheel and hammer are both working. The spectrum of the luminosity is confined to the more refrangible end of the spectrum, commencing somewhere about F, but it is difficult to say exactly. One difficulty in the way of observing the spectrum— and still more of photographing it-is the rapid rate at which this sugar wears out; and to overcome this the whole apparatus is fixed on rollers moved slowly along at a suitable rate to compensate for the change in the position of the sparks which would otherwise take place, and by this means the sparks or flashes of luminosity, which appear almost continuous, are made to take place always along the axis of the collimator of the spectroscope. The fact that the less refrangible part of the spectrum is absent shows undoubtedly that the luminosity cannot be due to the particles of sugar becoming red-hot or whitehot by the impacts, but seems to show that the light produced is due either to some change in the configuration of the crystals of sugar or to some sort of chemical action * Abstract of a Paper read before the British Association (Section A), Bristol Meeting, 1898. CHEMICAL NEWS. Preparation and Properties of Hydride of Calcium. set up between the sugar and the surrounding air at the freshly formed surface. To test the latter hypothesis, the spark has been produced by dropping a lump of sugar in a tall receiver, and it was found that the colour and intensity of the flash were independent of the pressure of the air-between 76 c.m. and 2 c.m. And likewise when coal-gas was substituted for air it was also found that wetting the surface of the sugar did not alter the effect; and when two lumps of sugar were struck in water, the interesting result was obtained that the light was-so far as could be judged by merely looking at it-precisely similar to that obtained in air and coal-gas. The fact that the surrounding medium does not seem to affect either the colour or intensity of the luminosity suggests that the effect is not due to any influence of a chemical nature of the surrounding medium on the sugar, but favours the former hypothesis that the luminosity is due to the peculiar structure of the sugar itself. The experiments are being pursued further. 157 independence of body and base renders it possible to pro duce the furnace at a lower cost than usual and facilitates packing and transport, and it has the further advantage that the cracking which takes place with all internallyfired fire-clay furnaces is less than in those made in one piece. For roasting, heating platinum and other small crucibles, cupelling, scorifying, and general muffle work an extra door is supplied, through which a muffle passes. The second figure shows this appliance, the body of the furnace having been removed from the base to show the arrangement more clearly, and the small door which closes the muffle aperture being shown drawn aside. The back of the muffle rests on a removable block, as shown. This furnace, which is about 13 inches in length, is found to be suitable for all the ordinary work of a laboratory, the various improvements in its construction also greatly facilitating the work done with it. NEW LABORATORY GAS FURNACE. OUR illustrations show a new fireclay gas furnace manufactured by Messrs. J. J. Griffin and Sons, on lines suggested by Mr. G. T. Holloway, for use by assayers, &c., or for performing any of the furnace work required in a chemical laboratory. FIG. I. From the first illustration it will be seen that the furnace base extends forward beyond the body, and forms a convenient stand for hot crucibles, &c., and for the doors when they are drawn forward. The deep flanges on the doors serve as handles for moving them when the FIG. 2. furnace is in use, and also support them in position and render them reversible. The base and body are made in independent parts, so that either may be replaced at small cost, and the base may reversed when spoiled on one side by slags, &c. This THE PREPARATION AND PROPERTIES OF By HENRI MOISSAN. Preparation.-Pure crystallised calcium, prepared by the method we described in a previous communication (Comptes Rendus, cxxvi., p. 1753, June 20, 1898) is put into a nickel boat in a glass tube traversed by a current of pure dry hydrogen. The hydrogen is purified by being passed through two porcelain tubes at a red heat,-one filled with copper and the other with pure boron. It is then dried with fused potash and phosphoric acid, previously calcined in a current of oxygen. At the ordinary temperature calcium does not react on hydrogen. When the tube containing the nickel boat has been well swept by a rapid current of hydrogen, the end of the tube is sealed and the hydrogen is kept in it at a pressure of from 30 to 40 c.m. of water. The temperature of the boat containing the lime is then slowly raised, and when it reaches a dull red heat we can see it take fire in the atmosphere of hydrogen. The gas is absorbed with great rapidity, and we obtain, in place of the metal, a white substance, which is hydride of calcium. If we perform this experiment on I or 2 grms. of calcium it may be done in a glass tube, but the great disengagement of heat produced by this combination may give rise to the reduction of the glass by the alkaline earthy metal, producing black spots on the glass by the setting free of small quantities of silicon. have already described, it is advisable not to work on When the reaction is carried out in nickel boats, as we more than 5 or 6 grms. of material at a time, or else the temperature becomes too high, and we more frequently find a crystallised alloy of nickel and calcium at the line of contact with the metallic nickel. When we wish to get a higher return of this hydride we can easily do so by putting several boats containing calcium in the tube, so that the reaction will be performed successively. The metallic tube is then placed on a gas furnace with eight jets, and by using three boats we can easily work with 15 grms. of calcium. If the hydrogen contains nitrogen, we notice that the hydride takes a greyish yellow tint and gives off ammonia by its decomposition with water. Properties.-Hydride of calcium is a white body, and after fusion has a crystalline fracture. Examined under the microscope it appears in thin transparent layers, some of which are again covered by very small crystals. It does not perceptibly dissociate up to a temperature of 600° in vacuo. Its density taken in essence of turpentine is 1'7. 158 Preparation and Properties of Hydride of Calcium, In hydrogen gas we have kept hydride of calcium intact up to a temperature of the melting-point of Bohemian glass; there was neither any absorption of gas nor apparent decomposition of the hydride. In a current of chlorine, hydride of calcium does not change to any perceptible extent in the cold; but as soon as the temperature is slightly raised, long before any sign of redness, it burns with a flame, certainly not very bright, but giving off fumes rich in hydrochloric acid. After this reaction there remains a mass having all the properties of chloride of calcium, but not containing any sub-chloride. When heated in the vapour of bromine at a dull red heat the reaction is much stronger, and the hydride decomposes with a brilliant incandescence. This same reaction occurs with iodine; a brilliant light is suddenly produced at a red heat, and at the same time there is a production of hydriodic gas. When heated on a sheet of platinum in free air, hydride of calcium undergoes no apparent change, even at a red heat, but if heated before an oxy-hydrogen blowpipe it burns with great brilliancy, producing at the same time a flame of hydrogen. After this experiment there remains only quicklime which has been raised to its melting-point. This residue treated with water forms at first a hydrate | of lime, which disintegrates forming a greyish powder, which on further treatment with water gives off hydrogen. In this strong combustion of hydride of calcium in air, a layer of lime is formed, which-on account of the heat given off by the reaction-melts, and thus covers a part of the hydride and prevents complete oxidation. When thrown into the flame of a Bunsen burner, powdered hydride of calcium gives brilliant sparks, as does lime. In a current of pure oxygen the hydride takes fire below a red heat, and continues to burn with strong incandescence. The heat given off is so great that one can distinctly observe the fusion of the lime produced. Examined under the microscope this lime appears to be covered with small crystals. We have already shown, by our experiments with the electric furnace, with what facility lime crystallises at a high temperature. Hydride of calcium, either in powder or in small lumps, when heated in the vapour of sulphur to a dull red heat. forms only a small quantity of sulphide, the decom. position not being complete. But if we heat a fragment of the hydride in front of the blowpipe, the reaction takes place immediately with brilliant incandescence; at the same time an abundance of sulphuretted hydrogen is given off. At the temperature of the melting-point of glass, hydride of calcium does not react on the vapour of sele. nium. When heated under a glass cover filled with nitrogen, hydride of calcium undergoes no change, even when the experiment lasts two hours. After cooling the volume of gas has not altered, and a sensitive litmuspaper gives no appreciable indication of ammonia. Thus, at a dull red heat nitrogen is without action on this hydride. On the other hand, hydride of calcium is decomposed by the vapour of phosphorus at about 500°. Hydrogen is given off, and a substance of a deep chocolate colour remains, which reacts with cold water, giving phosphuretted hydrogen. At a temperature of 700° boron has no action on hydride of calcium. When heated to from 700° to 800° in a crucible brasqued with previously baked charcoal, hydride of calcium is partially decomposed, and carbide of calcium, giving acetylene gas on contact with water, is formed. Under similar conditions silicon and boron gave no results. Fluoride of potassium, first melted and then powdered, was mixed with powdered hydride of calcium; this mixture heated in a test-tube gave no active result until a temperature of 500° was reached, when the hydride reacted and gave off hydrogen and vapour of potassium, Fluoride of sodium gave the same reaction. Fluoride of silver, when ground in the cold with this CHEMICAL NEWS, hydride, became incandescent, and degration was produced by the admixture of powdered nuoride of calcium and metallic silver. The fluorides of lead and zinc are reduced with incandescence below 400°. Chloride of sodium, reduced to a fine powder and mixed with hydride of calcium, undergoes at a red heat a regular decomposition, giving off vapour of sodium, which condenses, forming a metallic mirror on the cooler part of the apparatus. Melted iodide of potassium is not attacked by hydride of calcium, while iodide of silver, when warmed, reacts with a considerable disengagement of heat. Oxidising agents, such as chlorate or bichromate of potassium when melted, or powdered permanganate of potassium, are reduced with incandescence. The chlorates, bromates, and iodates form veritable explosives with this hydride. With perchlorate of potassium the explosion takes place in the cold, by the simple grinding of the two substances in an agate mortar. If a few m.grms. of the hydride are mixed with an excess of perchlorate of potassium, the explosion is sufficiently violent to smash the tube to pieces. Sulphuretted hydrogen does not read below a red heat, but at a higher temperature sulphide of calcium and hy drogen are formed. If we heat powdered hydride of calcium in an atmosphere of binoxide of nitrogen, before a red heat is reached, a lively incandescence is produced and ammonia is given off very freely. Carbonic acid is reduced at a red heat by hydride of calcium, with strong incandescence, carbon and carbide of calcium being formed. Warm concentrated sulphuric acid is reduced by hydride of calcium. Fuming nitric acid has practically no action. On the other hand, these same acids when diluted with water have a vigorous action; a salt of lime is produced, and hydrogen is given off. Concentrated or dilute hydrochloric acid attacks hydride of calcium. This reaction is comparable with that which gives us hydride of copper. Anhydrous ethylic alcohol attacks it but slowly, and both benzine and essence of turpentine, when quite free from water, have no reaction in the cold. The alcoholic chlorides and iodides are without action at the ordinary temperature. The vapour of tetrachloride of carbon is decomposed by this hydride with incandescence, at about 400°, with the production of a deposit of carbon and a disengagement of hydrogen and hydrochloric acid. The most curious reaction of this new compound is that which takes place with cold water; as soon as hydride of calcium comes in contact with this liquid, the latter is decomposed with violence, and both the hydrogen of the water as well as that from the hydride is given off, while hydrated oxide of calcium is formed: CaH2+2H2O=Ca(OH)2 + H6. Analysis. To determine the composition of the hydride of calcium, we made the following experiment:A given weight of pure crystallised calcium is placed in a small tared glass tube full of hydrogen. The exa& weight of the metal is taken, and then it is transformed into hydride. Weight of calcium 0'3595 grms. 0'3760" Hydrogen absorbed.. 00165,, which corresponds to the following centesimal composition: Theory for CaH,. 95'23 The 0'376 grm. of hydride of calcium is placed in a large gas measurer filled with mercury; into the upper part of the apparatus a few c. c. of water are passed, which immediately decompose the hydride giving a volume of CHEMICAL NEWS. Methods of Analysis applied to Silicate Rocks. hydrogen of 437.c. (H=766 m.m. T= +20°). The purity of this hydrogen was established by a eudiometric analysis. This volume, corrected to o° and 760 m.m. =40100 c.c. Th.oretically, if we give to hydride of calcium the formula CaH2 it should have produced a volume of 399.80 c.. Two other analyses, made under the same conditions, gave us the following figures :— Conclusions. To sum up, we obtain by the direct union of calcium and of hydrogen, a transparent crystalline hy. dride, with the formula CaH2. The hydride is stable at a high temperature, and is an energetic reducing agent. By its violent decomposition when in contact with cold water it strongly resembles the definite crystallised carbide of calcium we prepared in the electric. In this compound the hydrogen is comparable to the metalloids (carbon or phosphorus) and not to the metals. Even the appearance of this hydride completely distinguishes it from the hydrides of MM. Troost and Hautefeuille and the hydrogenised palladium of Graham. In reality there are two series of hydrides, some in which the hydrogen seems to be in solution in the metals, and the others forming at a more or less elevated temperature and presenting all the characteristics of definite chemical compounds.-Comptes Rendus, vol. cxxvii., No. 1. SOME PRINCIPLES AND METHODS OF Chlorine. To make sure of getting all the chlorine, it is best to fuse with chlorine-free sodium-potassium carbonate, or even sodium carbonate alone, first over the full burner, then for a moment or two over the blast, leach with water, acidify with nitric acid, and precipitate by silver nitrate. If i grm. of material has been used no precipitation of silica need be feared on acidifying or on standing. In many cases it is quite sufficient to attack the powder by hydrofluoric acid and a little nitric acid, with occasional stirring, and, after filtering through a large platinum cone, to throw down the chlorine by silver nitrate. The presence of nitric acid is necessary, since otherwise ferrous fluoride reduces silver nitrate with deposition of crystallised silver. When coagulated by heating and stirring, the precipitate is collected on the platinum cone, washed, dissolved by a little ammonia, and re-precipitated by nitric acid, when it can be collected in a Gooch crucible and weighed, or, if very small in quantity, on a small paper filter, which is then dried, wound up in a tared platinum wire, and carefully ignited. The increased weight of the wire is due to the metallic silver of the chloride which has alloyed with it. Fluorine. Fluorine can only be estimated by the method of Rose, tare being taken to use sodium-potassium carbonate as a flux, and to avoid use of the blast if possible. The use of ammonium nitrate or chloride instead of carbonate for throwing out the silica and alumina is not to be recommended, because of loss of fluorine on evaporation (Rose). If the rocks are very basic, it may happen that the amount of silica in the alkaline solution is so small that ammo. nium carbonate may be dispensed with and the ammoniacal zinc oxide solution added at once. 159 By whatever modification of the method the silica may have been separated, the alkaline carbonate must be converted into nitrate and not chloride if phosphorus or chromium, or both, are present. To remove the chromium and the last of the phosphorus, silver nitrate in excess is added to the solution containing still enough alkaline carbonate to cause a copious precipitate of silver carbonate, in order to take up the acid set free, and thus ensure a neutral solution and consequent complete precipitation of phosphorus and chromium. After heating and filtering, the excess of silver is to be removed by sodium or potassium chloride, and sodium carbonate is to be added, when the fluorine is ready to be thrown out by calcium chloride in excess. At this stage there must be no ammoniacal salts in solution, otherwise calcium fluoride may be held in solution. The well-washed and gently ignited calcium fluoride finally obtained in the course of this method should be converted to sulphate as a check upon its purity, and at the same time as a qualitative test to ascertain if it really is calcium fluoride by the characteristic odour of its gas. Should fluorine be found, and the weight of sulphate not correspond to that of the fluoride, the former should be dissolved in hot nitric acid and tested for phosphorus by ammonium molybdate solution. If phosphate is absent the impurity may have been silica or calcium silicatewhich of these it would be difficult to decide. In the former case the fluorine might be safely deduced from that of the sulphate, but not in the latter. If the rock were rich in sulphur it might happen that calcium sulphate would be thrown down with the fluoride, but this should be removed by thorough washing. If not, and it were certainly the only impurity present, the fluorine could be calculated, after conversion of the fluoride into sulphate, by the formula CaSO4-CaF2: 2F :: diff. between impure CaSO4 and CaF2 : x. It is an exceptional case when there is exact agreement between the weight of fluoride and sulphate, and with the small amounts usually met in rocks the error may be an appreciable one in percentage of fluorine, though of no great significance otherwise. There is no qualitative test which will reveal with cer tainty the presence of fluorine in rocks. Heating the powder before the blowpipe with sodium metaphosphate on a piece of curved platinum foil inserted into one end of a glass tube, or in a bulb tube, is not to be relied on in all cases. While as little as one-tenth of 1 per cent of fluorine can sometimes be thus detected with ease, much larger amounts in another class of rocks may fail to show. (To be continued). NOTICES OF BOOKS. The Extra Pharmacopæia. Revised in accordance with a small list of errata which should not be overlooked, but From the Bulletin of the United States Geological Survey, taking it altogether the author is certainly to be congratu No. 148, p. 15, 1897. lated in bringing out the present edition of a book so useful |