NEWS ance of the air is increased so much in proportion to the Eighth Annual Report of the Warden of the Standards THIS report contains much valuable information, of a From it we learn that the plan of coating weights with nickel, in order to exclude the action of the atmosphere, cannot be pronounced successful. Three of the larger weights, nickelised in 1872, were found in June, 1874, to have sensibly increased in weight, "tending to show that oxidation is going on under the nickel plating." It is unsatisfactory to find that "the teaching of the metric system of weights and measures, and the decimal scale in schools, under the authority of the Education Department, "has been formally abandoned by virtue of a notice in the "New Code of Regulations of the Education Department of the Privy Council, issued in 1874." This reactionary step will decidedly retard the much needed reform of our national weights and measures. An attempt made by the Swedish Government to introduce the metric system of weights and measures into the kingdom of Sweden, has been defeated in the Lower Chamber of the Diet by a very large majority. Molecular Equilibrium of Solutions of Chrome Alum.-M. Lecoq de Boisbaudran.-A mathematical paper, which requires the accompanying diagram. Determination of the Boiling-Points of the Chlorinised Derivatives of Toluen.-M. G. Hinrichs.-The same remark applies to this paper. Bulletin de la Societe Chimique de Paris, Saccharo-Carbonate of Lime and Hydrated Carbonate of Lime.-M. L. Bondonneau.-It has been observed long ago that solutions of sucrate of saccharate of lime, treated with carbonate of lime, do not deposit carbonate of lime, but that at a certain point the liquid thickens, and is converted into an opaline mass, decomposable into its elements by excess of carbonic acid and by heat. The mass thus formed has been viewed as a combination of saccharate and of carbonate of lime. The author remarked that the quantity of carbonic acid absorbed to form this magma varied according to the density in solutions of one and the same saccharate. He was hence led to the belief that sugar merely entered into the reaction by means of the increase of density which it occasioned, and that similar thickenings might be obtained with other aqueous solutions; which experience has confirmed in case of gum, dextrin, glycerin, and even of mineral solutions, such as nitrate of soda and chloride of sodium. The thickening is due, not to saccharo-carbonate of lime, but to hydrated gelatinous carbonate of lime. Cement for Marble and Alabaster.-Mix 12 parts of CHEMICAL NOTICES FROM FOREIGN Portland cement, 6 parts of slaked lime, 6 parts of fine SOURCES. NOTE.-All degrees of temperature are Centigrade, unless otherwise expressed. Comptes Rendus Hebdomadaires des Seances de l'Academie des Sciences, No. 11, March 22, 1875. Examination of the Procedures of the Human Mind in the Investigation of the Unknown by the Aid of Observation and Experiment.-M. Chevreul.- Not adapted for abstraction. Stability of the Salts of the Fatty Acids in Presence of Water, and on the Reciprocal Displacement of these Acids.-M. Berthelot.-The author finds that the alkaline salts of the fatty acids, in presence of water, behave like compounds intermediate between the salts of the strong acids, which are not apprecially decomposed by water, and the salts of the weak acids (carbonates, borates, &c.), which are partially decomposed by water in the ratio of its quantity, and with a tendency to the simultaneous formation of an acid salt and of free base. This analogy between the fatty acids and the weak acids becomes more striking as their equivalents rise; from formic acid, which is almost as energetic as the powerful mineral acids, to the valerianic, whose neutral salts easily become acid by evaporation; and to the stearic and margaric, whose alkaline salts (soaps) are so readily decomposed by cold water. Association in the Ural of Native Platinum with Rocks having a Basis of Peridote, and the Relation of Origin which unites this Metal with Chrome Iron. -M. Daubrée.-It is very probable that serpentine was the gangue in which platinum was originally disseminated, at least in the country of Nisché-Tagilsk. New Electro-Medical Galvanoscope.-M. J. Morin. -The author states that in the therapeutical application of continuous currents the use of the common galvanometer has the inconvenience of requiring preliminary regulation, which requires care and experience on the part of the operator. His new electro-medical instrument is free from this defect. Theory of Processes for Magnetisation.-M. J. M. Gaugain. Not suited for abstraction. sand, and I part of infusorial earth, and make up into a thick paste with silicate of soda. The object to be cemented does not require to be heated. It sets in twentyfour hours, and the fracture cannot be readily found. Certain New Bleaching Processes.-M. A. Brackebusch.-The methods generally used are not satisfactory, and hence attempts are being made to supersede them. (1) Cotton and linen tissues are brought in contact with oxide of zinc, dissolved in lye of potash or soda. There is no bleaching, properly so-called. The oxide of zinc combining with the textile fibre merely masks the natural colour of the latter. Possibly it may form colourless compounds with the colouring matters present. The alkaline liquids employed may affect the tissues. (2) It has been proposed to bleach wool and silk by immersion for an hour in a solution of 1 part common salt, and I part of oxalic acid in 50 of water. The influence of the oxalic acid is certain, though not explained. (3) Tessié du Motay takes about equal parts of permanganate of soda and of sulphate of magnesia, and dissolves them in luke-warm water. The tissues, previously freed from grease, are plunged into this bath till they are covered with a brown coating. They are then placedi na bath of sulphuric acid at 4 per cent, and rinsed after the brown matter is removed. They may be finally passed through sulphurous acid. (4) Ramsay forms his bleaching bath by sprinkling with water equal parts chloride of lime and sulphate of magnesia, when hypochlorite of magnesia is formed. This last process is highly recommendable. Use of Red Sanders.-Sanders-wood, despite its cheapness, is not much used in dyeing. The red matter is accompanied by a brown colour, which must be comculty. The principles found in sanders are―(1) A bitter, pletely eliminated-a process not unattended with diffibrown extractive matter, sparingly soluble in cold water, but readily soluble at a boil. (2) A red matter, santalin; insoluble in water, soluble in alcohol, strong boiling acetic acid, caustic alkalies, and hot alkaline carbonates. It undergoes a change if exposed to the air in a moist state, and is oxidised, especially in presence of alkalies. (3) Santalidin, one of the oxidation-products of santalin, is less insoluble in water than santalin, but dissolves more freely in the other solvents. Ths powdered wood, exhausted in boiling water to remove the brown matter, is 186 Chemical Notices from Foreign Sources. digested in a cold clear solution of chloride of lime as long as this becomes coloured. When this is done, it is carefully washed in cold water, and the dye-bath is prepared. A hot, but not boiling, solution of carbonate of soda is prepared, into which is put the wood contained in a linen bag, and the pan is tightly covered. Heat is applied without bringing it to a boil. When the bath has acquired a bright red colour with a violet tint, it is ready for use. The goods (woollen, cotton, or linen), mordanted in an acid bath, are plunged into the sanders beck till they have the wished for shade, and are then returned to the acid beck. Shades are thus obtained not inferior to madder work in brightness and solidity.-Muster Zeitung. [We copied this process from the notebook of a friend sixteen years ago, and are therefore much interested to find that it has been re-discovered.] Liebig's Annalen der Chemie und Pharmacie. Band 177, Heft 1, Feb. 27, 1875. {CHEMICAL NEWS, carbonates by fusion with bichromate of potash, to dry Les Mondes, Revue Hebdomadaire des Sciences. In noticing the death of Sir C. Lyell, M. Moigno remarks, "We have found, to our happiness, that in the last edition of this work ("The Antiquity of Man") the arguments which he had previously developed in favour of the indefinite antiquity of man have lost much of their value !" Determination of Glycerin and Succinic Acid in Wines.-M. Maumené.-The author holds that the quan Researches from the Laboratory of Prof. F. Beil-tity of these bodies, as produced by the fermentation of stein, of Petersburg. These researches comprise a paper on sulpho-butyric acids, by W. Hemilian; one on the bromine derivatives of ethan, by N. Tawildarow; and a note on the connection of substituted benzols and phenols, by F. Beilstein and A. Kurbatow. Chlorinised Xylidin obtained from Crystalline Xylol.-Pau! Jannasch.-The chlorinised xylidin (paraamido-xylol) is crystalline base, fusible at 92° to 93°, of faint unpleasant odour, resembling that of toluydin. It is extremely soluble in ether, alcohol, and benzol; scarcely soluble in cold, but moderately so in boiling water, from which it separates in fine foliaceous crystals. It evaporates readily along with watery vapour, and when heated in a hot current of steam it fuses to dull yellow drops. It combines with acids, forming a well-characterised and finely crystalline series of salts, which, however, in consequence of its feeble basic properties, are not very permanent. Communications from the Laboratory of the University of Erlangen.-Prof. von Gorup Besanez.-These comprise a paper on ratanhin, by Dr. B. Kreitmair; on peucedanin and its products of decomposition, by Dr. Gottlieb Heut, containing an account of the preparation and properties of peucedanin, and its behaviour with potash, with dilute sulphuric acid, with the halogens, and with nitric acid, and an account of oxy-peucedanin; further, a paper on the occurrence of thallium in carnallit, by Dr. F. Hammerbacher. From this it appears that Boettger had already demonstrated the presence of cæsium, rubidium, and thallium in the salts of the Nauheim brine springs. The author, therefore, examined carnallit and other Stassfurt salts containing potash in the same manner. In carnallit he found thallium, rubidium, and cæsium; in sylvin the two latter were recognised, but no thallium; polyhalit and kainit showed no traces of either thallium, rubidium, or cæsium. The Erlangen researches further contain a paper by R. Hornberger, C. Mutschler, and F. Hammerbacher on the ash of the fruits of Lithospermum officinale, and the wood of Calamus rotang and Bambusa arundinacea; and a notice by Prof. von GorupBesanez on ditain, a substitute for quinine, recently introduced into commerce, and obtained from Echitas scolaris. Behaviour of the Solutions of Certain Substances with Polarised Light.-O. Hesse.-A long and important paper; not capable of useful abstraction. glucose simultaneously with alcohol, will be proportionate to the latter, and that the exact knowledge of their amount may thus indicate the quantity of extraneous alcohol added to wine. He prepares hydrated oxide of lead by decomposing a soluble salt of that metal with potash, and after washing it well, suspends it in water. To half a litre of wine, concentrated by evaporation to 335 c.c., he adds oxide of lead enough to cause every trace of colour to disappear. A grey precipitate is formed. Filter, wash the precipitate, and evaporate to dryness in the waterbath. Treat the evaporated residue with absolute alcohol, holding a little hydrated oxide of lead in suspension. Stir, leave the mixture to stand for some hours, and filter. The liquid thus obtained is colourless. If submitted to a current of carbonic acid it grows turbid, but becomes clear again on filtration. It is dried at 110° C., and weighed as pure glycerin. To determine succinic acid, treat a litre of wine with albumen, or raw hide, in sufficient quantity to remove all the tannin. Mix with hydrated oxide of lead (after concentration) till the colour is entirely removed, and preserve the filtrate for the determination of glycerin. The precipitate is kept for a long time in contact with boiling water, containing about 10 per cent of nitrate of ammonia. The clear liquid, obtained on fresh filtration, contains all the succinic acid in the state of succinate of lead, besides other salts of the same base. It is treated with sulphuric (sulphurous?) acid, and filtered again, when we have a perfectly colourless liquid containing free succinic acid. After having heated to expel the excess of sulphuric (sulphurous ?) acid, the liquid is concentrated to about 100 c.c., and neutralised with ammonia. Heat sufficiently to expel any excess of ammonia, and add a few drops of ferric chloride, which has been previously kept for a long time in contact with sesquioxide of iron, so as to ensure the absence of free hydrochloric acid. Finally, collect the deposit of succinate of iron which forms, wash it well, ignite, and weigh the residual sesquioxide. This weight, 1978, gives the quantity of succinic acid existing in the quantity of wine analysed. MISCELLANEOUS. Lectures by Dr. Frankland.-Six lectures by Professor Frankland, on "How to Teach Chemistry," originally delivered to science teachers, will shortly be published by Messrs. Churchill, from notes taken and Methyl-Aldehyd, and Formic Acid Methylester.-edited, with Dr. Frankland's sanction, by Mr. George J. Volhard. The author obtains the former by means of Chaloner, F.C.S. a Davy's lamp fed with methylic alcohol, and the latter by distilling over formiate of lime wood spirit, saturated with hydrochloric acid. The same compound is obtained by decomposing hydrocyanic acid with hydrochlorated wood-spirit. Determination of the Carbonic Acid in Carbonates. -Julius Hessert.-Persoz proposed to decompose the Metropolitan Gas.-Dr. Le heby, the Chief Gas Examiner under the Board of Trade, has recently reported to the Corporation of the City of London, and to the Metropolitan Board of Works, the results of the daily testings of the gas supplied to London by the Chartered, the Imperial, and the South Metropolitan Gas Companies during the quarter which ended on the 31st of March last. April 23, 1875. Metropolitan Gas. 187 Now ready, Second Edition, price 38. 6d., MICROSCOPICAL being the Subject-Matter of a Course of Lectures delivered before the Quekett Microscopical Club. By W. T. SUFFOLK, F.R.M.S. Illustrated with Forty-nine Engravings and Seven Lithographs., London: HENRY GILLMAN, Boy Court, Ludgate Hill, E.C. Post free for 14 stamps, HOW TO MAKE MONEY BY PATENTS. BARLOW & CO., 23, Southampton Buildings, W.C. Applications to the Arts and Manufactures. Fuel: Production of Light: Secondary Products of the Gas Manu- facture. Compounds: Soda, Potash: Alkalimetry: Grease. At present there are nine testing places where the gas from the several works of these companies are daily tested by the officers appointed by the Corporation and the Metropolitan Board of Works, and the average results of the testings during the quarter have been as follows:-(1) With respect to Illuminating Power.-The common gas, when burnt at the rate of 5 cubic feet an hour from a Sugg's London argand burner, No. 1, with a 6-inch chimney, has, in the case of the Chartered Company, averaged the light of 17:37 standard sperm candles at Beckton, 16.86 candles at Friendly Place, Bow, and 16'92 candles at Ladbroke Grove, Notting Hill; while that of the Imperial Company has been equal to 16 17 candles at Carlyle Square, Chelsea, 16'04 candles at Camden Street, Camden Chemical Technology, or Chemistry in its Town, 16'93 candles at Graham Road, Dalston, and 16.22 candles at Bruce Terrace, Bromley. The gas of the South Metropolitan Company at Hill Street, Peckham, has been 15'94 standard sperm candles; and the cannel gas of the Chartered Company at Millbank Street, Westminster, has, with a Sugg's steatite bats'-wing burner, No. 7, burning at the rate of 5 feet an hour, given the light of 20'94 standard sperm candles. These results show that the illuminating power of the gas at each of the testing places has been fully equal to the requirements of the Acts of Parliament by which the companies are regulated. Purity. The gas of all the companies has been constantly (2) As regards free from sulphuretted hydrogen, and the average amounts of sulphur in other form than this have been as follows:In the Chartered gas-At Beckton, 10'97 grains per 100 cubic feet of gas; at Friendly Place, 13.18 grains; at Ladbroke Grove, 19:40 grains; at Millbank, 17.63 grains. In the gas of the Imperial Company, the proportions of sulphur have been 17:49 grains per 100 feet at Carlyle Square, 15.10 grains at Camden Street, 16-18 at Graham Road, and 10 89 grains at Bruce Terrace; while that of the South Metropolitan Company has been 18.33 grains per 100 feet. Dr. Letheby reports that the proportion of sulphur in the gas has exceeded the prescribed quantity on four occasions at Ladbroke Grove, on four occasions at Bruce Terrace, and on three occasions at Hill Street, Peckham. The excess at Bruce Terrace is reported to have resulted from accidental and unavoidable causes. all times absent from the gas of the Imperial Company at Ammonia has been at Bruce Terrace, Bromley; and the maximum amount in the same Company's gas at Graham Road, Dalston, was only 2-10ths of a grain per 100 cubic feet. At Carlyle Square it was o'7 of a grain, and at Camden Street 15 grains. In the Chartered Company's gas, the maximum amount at Ladbroke Grove was only o'4 of a grain per 100 feet; at Millbank, o'5 of a grain; at Friendly Place, 2 grains; and at Beckton, 3.8 grains. On two occasions, the ammonia in the gas at the last-named testing place exceeded the prescribed quantity of 2.5 grains per 100 cubic feet. The maximum amount of ammonia in the gas of the South Metropolitan Company was 1.6 grains per 100 feet. Silicates of Potash and Soda: Phosphorus, Borax: Nitre: Gan- Powder: Gun Cotton. Vol. I., Part 5, price 36s. Prussiate of Potash: Oxalic, Tartaric, and Citric Acids, and Appendices containing the latest information, and specifications relating to the materials described in Parts 3 and 4. BAILLIERE AND Co., 20, King William Street, Strand. South London School of Pharmacy, 325, Ken nington Road. Managing Director, DR. MUTER. Daily Lectures on the following subjects: CHEMISTRY. PHYSICS. MATERIA MEDICA. CLASSICS. The School has accommodation for 120 Students, and contains an excellent Museum and a very completely fitted Chemical Laboratory for 50 Junior and 20 Senior Pupils, with water and gas at every working bench. Registered Lodgings are provided for Country Students, where they can depend on comfort and economy. For all particulars, enclose a stamped envelope to the Secretary, Mr. W. BAXTER, at his office, Central Public Laboratory, Kennington Cross, London, S.E. BER ERNERS COLLEGE of CHEMISTRY.of the late Royal Polytechnic Institution and the Royal Naval College EXPERIMENTAL MILITARY and NAVAL SCIENCES under the direction of Professor E. V. GARDNER, F.E.S., &c. and from 7 to 10 p.m. daily. The Laboratory and Class Rooms are open from 11 to 5 a.m., and Especial facilities for persons preparing for Government and other examinations. Private Pupils will find every convenience. Analyses, Assays, and Practical Investigations connected with Patents, &c., conducted. For prospectus, &c., apply to Prof. E. V. G., 44, Berners-street, W REDONDA PHOSPHATE OF ALUMINA. Fro 8.85 20'17 100'00 rom the high percentage of Phosphoric Acid and Alumina, and its cheapness as compared with other Phosphatic materials, this article is worthy the attention of Manufacturing Chemists and Manufacturers of Manure. It is also specially adapted for Sewage purposes. For further particulars, apply to the Agents of the Importers: DUNN BROTHERS, CHEMICAL AND MINERAL MERCHANTS, ANDREW BELL & COMPANY, LIMITED, 33, KING ST., COVENT GARDEN, W.C. Carr Hall Iron Works, HASLINGDEN, LANCASHIRE. WILLIAM FOX, JOHN PAGE, (Late Page & Tibbs), 47, BLACKFRIARS ROAD, S.E., Continues to supply the Trade with Phosphorus, Chlorate of Potash Pure Acids, Pyrotechnic and all other Chemicals, Pure and Commercial Wholesale and Retail Chemist, at the Lowest Prices. Makers of every description of Chemical, Colliery, Copper Ore, Gold Mining and Glass Machinery, including Crown, German Sheet, and Plate Glass Plant, as supplied to some of the largest Firms in England, Ireland, Scotland, and Wales. Makers of the latest Improved Revolving Black Ash Furnace PATENTS. Mr. Vaughan, F.C.S., British with Siemens's Patent Gas Arrangement, and as used in the Manufac Foreign, and Colonial PATENT AGENT. Special attention given to Inventions relating to Chemistry, Mining, and Metallurgy. Guide to Inventors" Free by Post.-Offices, 67, Chancery Lane, London, W.C., and 8, Houndgate, Darlington. ture of Soda. THE CHEMICAL VOL. XXXI. No. 805. ON The author next describes a form of apparatus by which NEWS. measurable results are attainable. It consists of a long glass tube, with a wider piece at the end. In it is suspended a lump of magnesium by a very fine platinum wire, the distance between the point of suspension and the centre of gravity of the magnesium bob being 39'14 inches. Near the magnesium is a platinum spiral, capable of being ignited by a voltaic battery. Observations of the movement of the pendulum are made with a telescope with micrometer eyepiece. With this apparatus a large series of experiments are described, starting from air of normal density, and working at intermediate pressures up to the best attainable vacuum. The results are given in two tables. ATTRACTION AND REPULSION RESULTING By WILLIAM CROOKES, F.R.S., &c. PART II. THIS is the second part of a paper which the author sent to the Royal Society in August, 1873. The author commences by describing improvements which he has made in the Sprengel pump, and in various accessories which are necessary when working at the highest rarefactions. Continuing the description of apparatus, the author describes different new forms which enable the phenomena of repulsion by radiation to be observed and illustrated. A bulb 3 inches diameter is blown at the end of a glass tube 18 inches long. In this bulb a fine glass stem, with a sphere or disk of pith, &c., at each end is suspended by means of a cocoon fibre. The whole is attached to the Sprengel pump in such a way that it can be perfectly exhausted, and then hermetically sealed. Besides pith, the terminals may be made of cork, ivory, metal, or other substance. During exhaustion several precautions have to be taken, which are fully entered into in the paper. To get the greatest delicacy in an apparatus of this kind, there is required large surface with a minimum of weight. An apparatus constructed with the proper precautions is so sensitive to heat that a touch with the finger on a part of the globe near one extremity of the pith will drive the index round over 90°, whilst it follows a piece of ice as a needle follows a magnet. With a large bulb, very well exhausted, and containing a suspended bar of pith, a somewhat striking effect is produced when a lighted candle is placed about 2 inches from the globe. The pith-bar commences to oscillate to and fro, the swing gradually increasing in amplitude until the dead centre is passed over, when several complete revolutions are made. The torsion of the suspending fibre now offers resistance to the revolutions, and the bar commences to turn in the opposite direction. This movement is kept up with great energy and regularity as long as the candle burns. The author discusses the action of ice, or a cold substance, on the suspended index. Cold being simply negative heat, it is not at first sight obvious how it can produce the opposite effect to heat. The author, however, explains this by the law of exchanges, and shows that attraction by a cold body is really repulsion by radiation falling on the opposite side. According to the same law, it is not difficult to foresee what will be the action of two bodies, each free to move, if they are brought near to one another in space, and if they differ in temperature either from each other or from the limiting walls of the space. The author gives four typical cases, with experiments, which prove his reasoning to be correct. Experiments are described with the object of ascertaining whether the attraction by heat, which, commencing at the neutral point, increases with the density of the enclosed air, will be continued in the same ratio if the apparatus is filled with air above the atmospheric pres sure. This is found to be the case. Various experiments are described with bulb-apparatus, in which the bulb is surrounded with a shell containing various adiathermous liquids, and also with a shell of vacuum. In all cases radiation passed through, producing the normal action of attraction in air and repulsion in a vacuum. With this apparatus it was found that a candle-flame brought within a few inches of the magnesium weight, or its image focused on the weight, and alternately obscured and exposed by a piece of card at intervals of one second, will soon set the pendulum in vibration when the vacuum is very good. A ray of sunlight allowed to fall once on the pendulum will immediately set it swinging. The form of apparatus is next described which the author has finally adopted, as combining the greatest delicacy with facility of obtaining accurate observations, and therefore of getting quantitative as well as qualitative results. It consists of a glass apparatus in the shape of an inverted T, and containing a horizontal glass beam suspended by a very fine glass thread. At the extremities of the beam are attached the substances to be experimented on, and at the centre of the beam is a small mirror from which a ray of light is reflected on to a graduated scale. The advantage which a glass thread possesses over a cocoon fibre is that the index always comes accurately back to zero. In order to keep the luminous index at zero, except when experiments are being tried, extreme precautions must be taken to keep all extraneous radiation from acting on the torsion-balance. The whole apparatus is closely packed all round with a layer of cotton-wool about 6 inches thick, and outside this is arranged a double row of Winchester quart bottles filled with water, spaces only being left for the radiation to fall on the balance, and for the index ray of light to get to the mirror. However much the results may vary when the vacuum is imperfect, with an apparatus of this kind they always agree among themselves when the residual gas is reduced to the minimum possible; and it is of no consequence what this residual gas is. Thus, starting with the apparatus full of various vapours and gases, such as air, carbonic acid, water, iodine, hydrogen, ammonia, &c., at the highest rarefaction there is not found any difference in the results which can be traced to the residual gas. A hydrogen-vacuum appears the same as a water- or an iodine-vacuum. With this apparatus the effect of exposing a torsionbalance to a continuous radiation is described, and the results are shown graphically. The effect of a short (113 seconds) exposure to radiation is next described, and the results are given in the form of a table. In another table is given the results of experiments in which a constant source of radiation was allowed to act upon one end of the torsion-beam at a distance of 140 or 280 millims., various substances being interposed. The sensitiveness of this apparatus to heat-rays appears to be greater than that of an ordinary thermo-multiplier. Thus the obscure heat-rays from copper at 100°, passing through glass, produce a deflection on the scale of 325, whilst under the same circumstances no current is detected in the thermo-pile. The following substances are used as screens, and the deflections produced, when the source of radiation is magnesium wire, a standard candle, copper at 400°, and copper at 100°, are tabulated :— Rock-salt, 20 millims. thick; rock-crystal, 42 millims. thick; dark smoky talc; plate glass of various thicknesses, both white and green; a glass cell containing 8 millime • Abstract of a Paper read before the Royal Society, April 27, 1875. of water; a plate of alum 5 millims. thick; calc-spar, |