It will be seen that the lines (EE', FF', and GG', &c., of Fig. 2) joining points represented on curve A B of Fig. I do not intersect at a common point; also the solids, upon examination, showed a great resemblance to yttrium hydroxide. Therefore the precipitates along this line can only be solid solutions. Lines joining any points along the curve B C (Fig. 1) meet at a common point x, which corresponds to a definite hydrated basic nitrate of yttrium possessing the formula 3Y2O3.4N2O5.20H2O. The basic nitrate consisted entirely of small crystals, which were rapidly decomposed by water. The compound, however, was not affected by continued washing with absolute alcohol, and, since the normal nitrate is very soluble in this liquid, it could be entirely separated from the basic nltrate. The solids from several bottles along the curve B C were filtered upon a Hirsch funnel, washed with absolute alcohol, air-dried, and analysed. The results obtained were as follows:- : For this compound the authors offer the following complex formula :— (NO3)2Y—O—Y-O-Y-O-Y-O-Y~O~Y(NO3)2 +20H2O NO3 NO3 NO3 NO3 NO, NO3 From the foregoing work the following conclusions are drawn: First, that the basic compound mentioned by Bahr and Bunsen does not exist. Their results were undoubtedly due to adherent normal nitrate. Secondly, the only basic nitrate that does exist at 25° is the one corresponding to the formula 3Y203.4N2O5.20H2O. Thirdly, this compound is stable in air, and can exist in contact with water containing more than 33 grms. of yttrium nitrate to 100 grms. of water.-Journal of the American Chemical Society, xxxii., No. 7. THE use of lead in the foundry goes back to the remotest period of human industry. Its general properties are well known, and when by intent or carelessness they are violated, the founder soon discovers his mistake without much difficulty; its application within very narrow limits is well understood by all practical metal workers. So important a factor has lead become in every foundry where a diversified range of castings is made that it has been deemed necessary to determine the percentage of that element in any form of alloy in which lead may be present. To accomplish this end chemists have made exhaustive researches to discover assay methods that should be accurate, easily conducted, and conclusive. In this paper the methods of assay referred to apply to the alloys into which lead enters in the course of foundry practice rather than to the ores in which lead occurs. A Paper read before the American Brass Founders' Association. From the Chemical Engineer, xii., No. 6. Gravimetric Methods. Alloys not containing tin may be proceeded with directly for the determination of lead, but if tin be present the alloy is dissolved in nitric acid, evaporated to dryness on the water-bath, diluted, allowed to settle, filtered, and the filtrate treated with 2 to 3 cc. of H2SO4, evaporated until fumes of SO3 are driven off, cooled, diluted with 20 to 30 cc. of water, washed with dilute H2SO4 or alcohol, the filter, the paper and the precipitate ignited separately, or both, dried in the steam-bath, precipitate detached from their ashes united, a drop of nitro-sulphuric acid added, gently dried, and re-ignited and weighed as PbSO4, or the precipitate is filtered through a Gooch crucible and dried at 105° C. to constant weight. This method is very old, but is reliable only in the most skilful hands. In the incineration of the paper-filter there are two sources of loss, the oxidation and volatilisation of lead, and the difficulty of re-converting every particle of the lead reduced by the carbon of the filter back to the form of a sulphate. To overcome these difficulties the Gooch crucible is resorted to. Dr. Bollenbach (Zeit. Ann. Chem., 1908, p. 690), states, however, that this sulphate reaction is not very convincing because the precipitate is soluble in strong nitric acid, and he proposed the precipitation of lead as a peroxide in an ammoniacal solution by means of bismuth, and gives his method in detail. In his paper on the volumetric assay of lead Dr. J. F. Sacher (Chem. Ztg., Dec. 2, 1909, p. 1257) states that the precipitation of lead as lead molybdate offers an advantage over that of the sulphate method, as the molybdate salt is less soluble in water than the sulphate. In a nitrate solution of an alloy not containing arsenic, arsenates, nor phosphoric acid, ammonium molybdate may be used directly as a reagent for the quantitative separation of lead. Jannasch (Ber., xxvi., 2329) has proposed a gravimetric separation of lead and copper from a nitrate solution by means of the hydrogen peroxide method, of lead from tin and zinc, metals which are of vital importance, and while these methods are of great importance to the research chemist, they are, on account of limited use in the everyday routine of the foundry. the difficulties incurred in the ignition for weighing, of About the best example that can be offered of the importance of the gravimetric method is that of the determination of lead in babbit metal by Messrs. Walker and Whitman (Fourn. Ind. and Eng. Chem., August, 1909). Dissolve to i grm. of alloy in a 250 cc. beaker until the sample is in complete solution. Evaporate to with 20 cc. HCI, 5H2O, and add HNO3 a little at a time dryness on a steam-bath, add 5 cc. strong HCl (if sample contains 10 per cent or more lead add 10 cc. HCl), warm a few minutes, stir in 150 cc. of 95 per cent alcohol, allow to stand at room temperature for two hours, filter through a Gooch crucible, wash with about 100 cc. of 95 per cent alcohol, dry crucible in air-bath for one hour at 105° C. Weigh as PbO2, add o'0085 grm. to the weight of the precipitate, and multiply by o'74473 to find the weight of metallic lead. Volumetric Methods. Numerous methods have been proposed for this determination; the three most prominent are Alexander's molybdic acid method, as modified by Low, the ferrocyanide method, and the permanganate method. Alexander's original paper was first published in Berg- u. Huttenm. Ztg., 1893, p. 201; Low's modification in Journ. Am. Chem. Soc., xv., 550. He employs a solution of 4:25 grms. of the salt to the litre, which if grm. be weighed out for the assay corresponds I cc. to 1 per cent of lead. Dissolve o 2 grm. of pure lead in HNO3, evaporate with H2SO4, filter off the lead sulphate, and wash with dilute H2SO4. The sulphate is decomposed with 25 cc. strong HCl, add 15 cc. HCl and 25 cc. water, and saturate with 25 cc. strong ammonia (sp. gr. o'90). Finally, acidify with strong acetic acid, dilute with 200 cc. of water, heat to ebullition, and titrate, CHEMICAL NEWS Jan. 27, 1911 } Determination of Lead in Non-ferrous Alloys.. The ferro-cyanide method is carried out with a lead acetate solution acidified with acetic acid, and titrate with a ferro-cyanide solution which contains 10 grms. of this salt to the litre. One cc. of solution for a i grm. assay corresponds to about 1 per cent of lead. Titrate till a drop taken out with a drop of saturated uranium acetate solution gives a characteristic brown colouring upon a porcelain plate. Low digests the lead sulphate with saturated ammonium carbonate solution to convert the sulphate into a carbonate, cools, filters, and dissolves the carbonate in a mixture of 5 cc. concentrated acetic acid and 25 cc. water, dilutes 100 cm. water, and titrates. If Sb or Bi are present then the lead sulphate is first of all treated with 10 cc. H2SO (1:1) and 2 grms. of Rochelle salts, add 40 cc. water, and boil. Dr. Bollenbach's method is a modification of the permanganate method (Zeit. Anal. Chem., 1907, p. 582), but his method is a reversal of all former procedure. In a hot solution of potassium permanganate he adds the lead solution, made alkaline by NaOH, drop by drop to complete discoloration, adds some barium sul phate to facilitate the titration; but his method has recently been studied by Dr. J. F. Sacher, who states that the behaviour of BaSO, towards KMnO4 is completely indifferent, and that the method proposed is unreliable. Dr. Sacher advocates the adoption of the molybdate_method (Chem. Ztg., December 2, 1909, p. 1257), which he modifies as follows:-To conduct the titration there is required an ammonium molybdate solution of which I cc. corresponds to o'or grm. Pb and a 3 per cent tannin solution. In addition there should be a lead nitrate solution containing 16 grms. of Pb(NO3)2 in water to the litre, of which I cc. corresponds exactly to o'or grm, of Pb, and ready for the back titration when necessary. With this solution the rest of the molybdate titration may be quickly controlled. The tannin solution must be freshly prepared, as it is not unalterable, a 2 per cent addition of acetic acid will prolong its sensitiveness toward the molybdate solution for one week; alcoholic tannin is more permanent, and is suitable as an indicator. Applied to a bronze alloy, for example, the procedure would be to dissolve about o'5 grm. in from 4 to 5 cc. of HNO3 (sp. gr. 142), evaporate to dryness, dilute with water in the usual way, filter off the metastannic acid, precipitate the copper with the electric current or as a sulphocyanate, and determine the lead in the filtrate from the neutralised nitrate solution. Add 5 cc. ammonia, dilute to 100 cc. with hot water, allow to stand on water-bath two to three minutes, add 5 cc. of 80 per cent acetic acid, and titrate hot with ammonium molybdate. The volume of the titrated fluid is carefully measured, and the excess in molybdate corresponding to this volume, which occasioned the first yellow colouring with the tannin solution, is deducted from the cc. of molybdate_solution found. A concentration below o'15 per cent Pb is to be avoided, because such a condition makes the end-point indistinct. In such a case the colorimetric method is preferable. The best results are obtained if the precipitate is allowed to settle on the water-bath from two to three hours. To be filtered cold, wash with water till the filtrate shows no more turbidity with the neutral lead solution, dry at 100° C., ignite gently after separate incineration of the filter, and weigh after cooling as PbMo04. A large percentage of iron in the alloy interferes with an accurate result. This may be avoided by precipitating the excess of iron as a hydroxide in the presence of acetic acid. A new and simple volumetric method has recently been proposed by Dr. Rupp (Chem. Ztg., Feb. 8, 1910, p. 121), as follows:-Twenty or 25 cc. of a half normal solution of potassium cyanide is rinsed into a 100 cc. flask, mixed with a suitable volume of lead solution (1 to 5 per cent) free from acid. Fill up to the mark, mix thoroughly, filter after five to ten minutes, and titrate 50 to 75 cc. of the filter with quarter to half normal acid to determine the excess of alkaline cyanide. Use methyl-orange as an indicator. If the lead salt solution contains any acid in a 45 free state it is made exactly neutral with dilute NaOH in The cyanide solution may be standardised against a pure metallic lead or pure metallic copper in the usual way, using 98 to 99 per cent pure potassium cyanide. The accuracy of the method is ensured by the absence of free acid in the lead solution. For an alloy containing a small amount of lead, say, less than o'15 per cent, the colori. metric method has no rival for accuracy, neatness, and dispatch. Iron, however, in the ferric state introduces an inaccuracy. The solution should be dilute neutral and a nitrate. The method is based upon the comparative colour intensity of two liquids of the same concentration and volume, of an unknown with a known value. This analysis may take place in one of two ways :-A known solution of a definite volume and known concentration may be compared with an unknown solution having the same volume, and, if it have the same concentration, it will have the same depth or tint of colour that the known solution exhibits. With coloured fluids that are stable a series of concentrated solutions may be kept in readiness as a basis of comparison. In the second method, use is made of the fact that two solutions of different volume densities appear to be equally coloured if their concentration is inversely proportional to the intensity of their colour. In a special colorimetric apparatus the height of the column of the liquid is altered until both have the same intensity of colour, and calculate the desired concentration from the proportion of the depth of the two columns. Method.-Mix the given lead solution with an excess of sulphide solution, and select from a series of similarly treated comparative solutions of various but of known constitution which has been previously prepared from a pure lead nitrate, the one which appears to have the same colour for the same volume. Its concentration will be the same as that of the solution which is being tested. Execution.-Use a colorimetric apparatus if possible. Dry at 120° a re-crystallised sample of purest merchantable lead nitrate, weigh out o'o160 grm. of it, and dissolve in a measuring flask. Dilute to 1 litre. With the solution (A) containing o'or mgrm. of Pb per cc., fill up a burette. In graduated cylinders put 40, 30, 20, and 10 cc. of this fluid, dilute each to 50 cc. Prepare in addition four other solutions (B, C, D, and E), which contain o·008, 0·006, 0'004, and o'002 m.grm. of lead per cc. In one of ten about equally wide and high reagent glasses place upon a label a mark removed about 3 cc. from the edge, and indicate exactly the same (measured from the bottom) height in the same way, in the rest of the nine glasses. Fill up No. 1 with the lead solution to be tested; Nos. 2 to 6 with the comparison solutions A, B, C, D, and E. Fill up No. 7 with pure distilled water to the mark. Now, in each of the seven glasses add from 3 to 4 drops of colourless (i.e., 10 per cent) ammonium or natrium sulphide solution, shake or stir the fluids thoroughly, compare the colours. In making the comparison hold or place the two vessels against a background of opaque white glass. The examination should take place in a diffused light of uniform illumination. As soon as it is established between which of the concentrations the unknown lead solution lies, then prepare three additional comparison solutions of intermediate concentration, so that the lead constituent of one to the other bears the relation of about o'0005. Pour this into reagent glasses Nos. 8, 9, and 10, and compare them likewise with the solution of unknown strength. Set their colours (for example, between those of C and D, i.e., o'006 and 0.004 mgrm. per cc.); thus the new solutions have o'0055, 0.0050, and 0.0045 mgrm. per cc. Therefore the 27°5, 25, and 22.5 cc. of the solution A are to be diluted up to 50 cc. Repeat this until constant results are obtained; the concentration up to o‘o005 mgrm. of Pb is exactly determined. If the lead constituent in the given solution rises above o'or mgrm. per cc., then the sulphide addition causes too great a darkening for the comparison, and the fluid is correspondingly diluted. Mgrms. of lead should be expressed in cc. Woudstra (Zeit. Anorg. Chem., lviii., 168) states that the method by H2S is inexact in the presence of Fe. In the Fourn. Soc. Chem. Ind. (Jan. 15, 1910, p. 7) J. M. Wilkie takes exception to the use of a sulphide salt alone as a source of colour comparison; he prefers to add a solution of KCy or hydrocyanic acid to the lead solution previously made alkaline with ammonia. Iron present must be in a ferrous state, and ferrous hydroxide must be precipitated under conditions that ensure its intimate contact with KCy. Sodium sulphite is used as a reducing agent. The solution to be tested must be colourless before the alkaline sulphite is added. If the solution to be treated is not acid it is to be acidulated with a few drops of acetic or other acid to a distinctly acid reaction, I cc. of a 10 per cent solution of KCy is then added, and finally a considerable excess of ammonia, if colourless add the sulphide. If the iron is present originally in the ferric state add a few drops of N/10 sodium thiosulphate, heat slowly to incipient boiling, allow to stand until the colour suddenly bleaches out, then add KCy and NH4OH as usual. Centrifugic Method. In the Chemiker Zeitung Repertorium of Feb. 13, 1909, there was published an account of the "Centrifugic Method" used successfully by an Italian chemist in the works of Ansaldo, Armstrong, and Co., in Cornigliano, Liguria. According to the supposed lead constituent he weighs out from 0.5 to 5 grms. of the alloy to be tested, treat with HNO3 in the same way as in a solution for the determination of lead sulphate, filter off the metastannic acid, evaporate the filtrate with H2SO4 until white fumes appear, cool, dilute with 20 cc. of water. Use a centrifugal apparatus. The tubes used are graduated somewhat similar to that of a burette. A certain factor dependent upon the weight taken is used in obtaining results. If 2 grms., for example, have been weighed out and the tube reading is at the twelfth division, then by multiplying this reading by the factor o'2274 the lead content becomes 2.728 per cent of Pb. Frank Castek (Osterr. Zts. Berg- u. Huttenm., 1909, Ivii., 665-684) uses a phosphorus centrifuge machine, and prefers the ammonium molybdate precipitation of lead to that of the sulphate. His conclusion is, that applied to ore containing less than 35 per cent, using I grm. for a determination, the results are concordant, but somewhat too high; 14 tests could be made in five hours. Planimetric Method. The planimetric method of assay of lead in non-ferrous alloys may safely be described as the latest to arrive among us. It is essentially a microphotographic method. In a non-ferrous alloy containing many ingredients it would be necessary to eliminate tin, copper, antimony, and arsenic in the usual manner, and reduce the alloy if possible to such a state as to contain but two metallic ingredients, preferably zinc and lead. Obtain a sulphate solution, evaporate to dryness until fumes of SO3 escape, and transfer the same to a porcelain crucible, reduce and ignite to a prill or button of lead, allow to cool, remove the prill, flatten carefully, and etch with dilute nitric or sul phocyanic acid, and take an enlarged microphotograph of the same. Prepare several standard micrographs of leadzinc alloys or lead alone, or lead and tin, or lead and copper, or lead and antimony, or lead and arsenic, with the planimeter in the usual way, measure the lead area shown by the microphotograph, and by the method of proportion compare the areas of lead in the unknown compound with the areas of the known compound. To anyone familiar with operating a planimeter the method becomes exceedingly fascinating, and if the buttons or prills of a known composition are carefully prepared and clearly photographed to scale, the results are accurate and con Lead is deposited from a strong nitric acid solution at the anode as PbO2. To facilitate the deposition, the anode should revolve about 500 revolutions per minute. The current density should be about 5 ampères, and the terminal pressure between 3 and 4 volts; after ten minutes, interrupt the current for some seconds in order to accelerate the reduction of the metallic lead separating at the anode, and repeat this once again towards the close of the assay. After thirty minutes, test the solution for lead with ammonium sulphide. When the work is finished, shut off the current, dip the anode wire or gauze in hot water and then in alcohol, and dry for an hour at 230° and weigh. The weight of the PbO2 found multiplied by 0.866 according to H. J. S. Sand and E. F. Smith, by 0-8643 according to A. Staehler, but by o'857 according to Hollard and Bertiaux. This discrepancy is due to differences of the thoroughness in the expulsion of the water from the deposit. The question has been carefully studied by H. J. S. Sand. He dried the deposits in a specially contrived drying oven where he could maintain a temperature almost constant between 230° and 240° C. It is my conviction that this empirical factor must be established by a series of experiments that apply to the oven itself and the conditions under which the assay is conducted. igniting the PbO2 to PbO as suggested by Treadwell, which can be done if a platinum dish be used as the anode, this difficulty of drying at a constant temperature may be overcome and with more accurate results. In conclusion, the writer would say that the last method is the best of all for rapid accurate work. By REPORT ON CHEMICAL CONSTITUTION AND THE ABSORPTION OF LIGHT.* By W. W. STRONG. A Method of Chemical Analysis. RESEARCH along many lines in science is often very much stimulated by the requirements of technology. This is especially true in connection with many branches of organic chemistry, and a good example is furnished by the pure food laws. In regulating the use of various colouring and preserving matters added to foods, it is necessary that the examiners shall be able to recognise various compounds easily and quickly. Many organic compounds possess very characteristic colours, and it has often been asked whether the absorption spectra of these compounds would aid in their analysis. Our present knowledge of absorption spectra is mostly limited to the visible region of the spectrum. Before this method of analysis can reach its full service to chemists it will be necessary to measure the absorption throughout the region of the infra-red. At present the absorption spectra of a few potassium salts have been explored to regions of wavelengths as long as o'i mm. (Electro-magnetic waves having wave-lengths between 8000 m. and 6 mm. have been produced). The analysis of inorganic compounds is probably less hopeful, although the absorption spectra would often help to identify compounds. A great many of the inorganic cations show characteristic absorption in the visible portion *This Report is based upon an article by H. Ley, entitled " Ueber die Beziehung Zwischen Lichtabsorption und Chemischer Konstitution bei Organischen Verbindungen." See Jahrbuch der Radioaktivität und Elektronik, 1910, vi., 274. From the American Chemical Journal, xliv., No. 1, CHEMICAL NEWS, Jan. 27, 1911 Chemical Constitution and the Absorption of Light. of the spectrum and practically all have bands in the infra-red. J. Formanek has suggested that the presence of metals in metallic compounds of alkannin could be determined from the absorption spectra of these compounds ("Die Qualitative Spectralanalyse Anorganischer Körper"). The following measurements of the absorption bands of the different compounds of alkannin show the effect of the metal upon the position of the bands : An 47 Our present theory of the mechanism of the absorption and emission of radiations is very simple. Light and heat are electro-magnetic radiations, and hence the emitter and the absorber must either be an electric charge or a magnetic pole. As free magnetic poles are unknown to us while free electric charges are known, this theory makes the electric charge the origin of all electro-magnetic phenomena. At present no positive electric charges are known to be associated with portions of matter smaller than the hydrogen atom. On the other hand, negative electrons are known to be associated with masses only about one two-thousandth that of the hydrogen atom. As far as experiment shows, these electrodes always have the same properties and the same charge (the charge is invariably considered as constant when e/m varies), no matter from what element they may come. It is for these reasons that the electron is made the basis of all electro-magnetic theory, and at present there are but few phenomena capable of any explanation which cannot be explained by this theory. Electro-magnetic radiations then have their origin in electric charges. Continuous spectra (as from hot metals) are due to free electrons, and these apparently have very little connection with the chemical constitution of the métal molecules. Fine line and band spectra are apparently due to different systems of electrons within the atom, and are greatly affected in intensity by the presence of neighbouring atoms. The electrons of this type vibrate in definite fre The use of absorption and emission spectra has been very successful in studying the elements of the rare earths, and has been very extensively applied by Crookes, Becquerel, Exner, Demarçay, and many others. account of this work is given by Böhm ("Die Darstellung der Seltenen Erden," Leipzig, 1905). Recently, Urbain (“Le Radium,” June, 1909) has employed the phos-quencies that can be changed only very slightly by changing phorescent spectra in the purification of compounds of europium, gadolinium, terbium, dysprosium, neoytterbium, and lutecium. Atomic Structure and Spectra. The greatest interest lies, however, in the relation between chemical constitution and absorption or emission spectra. The relation between flame, spark, and arc spectra and the chemistry of the emitters is not known. The source of spectra like that from the blue cone of a Bunsen burner, the Swan spectra, is at present a much mooted problem. It is probable that chemical reactions play an important role in the emission and absorption of spectra, and especially of band spectra. We usually think of most spectrum lines like D1 and D2 of sodium as coming from the metallic atoms. Fredenhagen points out that under most conditions oxygen is present (Phys. Zeit., Oct. 24, 1907). In chlorine, hydrogen, or fluorine flames, calcium, strontium, thallium, sodium, barium, and copper emit spectra that are very different from those obtained when oxygen is present. Under these conditions thallium does not emit the characteristic green line and the lines D1 and D2 are completely absent. Work on the absorption of sodium, mercury, potassium, and various other vapours show that the presence of foreign gases modifies the character of the absorption very much. Many believe that certain series or groups of lines are due to chemical reactions of various kinds. Chemical reactions and processes of ionisation and recombination are believed to place the atom or molecule in a peculiar condition, in which it can emit energy to the ether or absorb energy from it. Under ordinary conditions the atom does not seem capable of doing this. In sodium vapour, for instance, according to present theories only one atom in thousands is taking part in absorption at any one time. The problem as to how energy is transferred to and from matter is one of the most fundamental problems of science. A striking example of the fact that a few atoms under peculiar conditions have the power of absorbing an enormous amount of energy from the ether is exhibited by the iron absorption lines in the solar spectrum. An arc of carbon electrodes containing iron as an impurity emits enough iron vapour to absorb as much as the iron vapour in the sun. It is thus seen that an infinitesimal amount of iron in the very great atmosphere of the sun is sufficient to absorb a large part of the energy emitted by the photosphere. the external conditions. The Absorption Spectra of Organic Compounds. The Unit of this Absorption. In discussions concerning the colour of organic compounds it is customary to speak of the selective absorption as being due to certain ions or molecules. This is probably true in the infra-red; the electric charges absorbing these long wave-length radiations are probably associated with masses of molecular size. But in the visible and ultra-violet portions of the spectrum the value e/m of the absorbers is invariably of the same magnitude as that of the electron. Drude (Ann. Phys., 1904, xiv., 677, 726, 936, 961) has investigated a large number of organic compounds, and shows that the absorber of all the shorter waves of the spectrum is the negative electron. Houstoun (Nature, May 20, 1909; Proc. Roy. Soc., 1909, A, lxxxii., 606) has calculated the value of e/m 1297 V K 1-0 for the absorption bands of several organic compounds, and also shows that the absorber is the electron (V is the refractive index, K the maximum value of the coefficient of extinction; A is the wave-length of maximum absorption, and A, is the wavelength for which the coefficient of extinction has a value equal to half its maximum. The formula used is based on the present theories of dispersion). The following table is from Houstoun : Compound. λο Fuchsine in alcohol.. 1-6(10) 5'4" 8.1 " Throughout the present paper the absorbers are considered as negative electrons. These electrons have certain free periods corresponding to the bands of selective absorption. These free periods are greatly modified by the presence of certain chemical radicals, and seem to be electrons that are situated either in the outer parts of the atom or between two or more atoms. Stark and others call these the valency electrons, and consider that chemical valency is due to them. Chemical bonds will then be closely associated with the electric fields of these electrons " While the theory in its present state is confronted with many difficulties, yet it seems a step towards the explanation of the more or less vague chemical bond. As an aid to our imagination, we shall consider atoms or ions as large spherical regions throughout which a positive charge is uniformly distributed. These regions are sometimes spoken of as "spheres of influence." Two atoms collide when their "spheres of influence " touch. Groups of atoms composing ions, radicles, or molecules, will have "spheres of influence. No ion can penetrate the sphere of influence of another atom or molecule. On the other hand, the electrons are very small, and bear much the same relations in size to the atom that the sun bears to the solar system. The electric fields of the electrons occupy quite large volumes, however, although the energy of this field is mostly situated in a very small space. Electrons can therefore move through ions and atoms if they have sufficient velocity. In most organic compounds it is considered that the valency electrons move in the interatomic spaces with considerable ease. In the metals a large number of the electrons are free. In organic compounds that are transparent to certain wave-lengths, the electrons in general will be held within certain regions by forces which are supposed to be elastic in their nature. ALEXANDER C. CUMMING, Esq., Chemistry Department, University of Edinburgh. DEAR SIR, I have noted with much interest your note in the CHEMICAL NEWS on " Efflorescence of Washing Soda Crystals." The presence of the extra half molecule of CO2 is difficult to explain, as in fifty years' experience I have never found "soda crystals take up CO2 from the air. I would venture to suggest a possible origin for the crystals you examined. In old days, when alkali contained much sulphate, it was easy to obtain large perfect crystals of hydrated monocarbonate of soda, but it was most difficult to prevent their falling to pieces under a shade. Therefore for exhibition purposes we used to expose them to an atmosphere of CO2, and if carefully done the bicarbonate (or sesquicarbonate as the case might be) preserved the form of the original crystal, forming an opaque pseudomorph of perfect shape. If this is the origin of the carbonic acid in these crystals, it in no wise takes away from the interest of the formation of a true sesquicarbonate.-I am, Yours faithfully, DAVID HOWARD. MONDAY, MEETINGS FOR THE WEEK. 30th.-Royal Society of Arts, 8. (Cantor Lecture). "Etching," Ir must be admitted that the author of this book had a Seeing the Invisible. By JAMES COATES, Ph.D., F.A.S. TUESDAY, by F. Wedmore. 31st.-Royal Institution, 3. "Heredity," by Prof. F. W. Mott, F.R.S., &c. Royal Society of Arts, 4.30. "Tin Resources of the "Examinations and THE sub-title of this book, "Practical Studies in "Grouse Disease," by A. E. Shipley, F.R.S. "Problems in the Career of SATURDAY, 4th.-Royal Institution, 3. the Great Napoleon," by Arthur Hassall, M.A. |