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The amount of knowledge now required for a boy to be successful in the above professions is very great, and can only be acquired by his taking a regular course from an early age.

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THE CONSTITUTION AND STRUCTURE OF ATOMS. (Continued from Chemical News, October 11, 1907).

BEAM, 6 ins. CAPACITY, 200 grms. SENSITIVENESS, 0.5 mgrm. Agate knife-edges and planes.

7-8, Idol Lane, Great Tower St., London, E.C., Licensed Trader in Alcohol and Spirits of Wine. Stock kept in suitable packages ready for immediate use.

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I grm. of hydrogen occupies 11160 cc.), is given by

VOL. CI., No. 2625.

A NEW METHOD FOR DETERMINING VAPOUR DENSITIES.*

By PHILIP BLACKMAN.

Apparatus.

A LONG glass measuring-tube (a disused burette serves the purpose excellently) has one end sealed off, and the other open end has a projecting rim or lip (Fig. 1). A one-holed rubber stopper, to fit the measuring-tube, is fitted with a glass N-tube of narrow bore (2 or 3 mm. internal diameter) of the shape shown in Fig. 2; its end must be flush with the stopper as shown. A small glass-stoppered weighingbottle, best of the shape and size shown in Fig. 3, because it will lie conveniently across the measuring-tube without jamming (it is supplied by Messrs. F. E. Becker and Co., Ltd., 17-27, Hatton Wall, London, E.C.) is used for weighing out the substance to be experimented upon.

Method.

1. The measuring-tube, placed upright, is filled with dry clean mercury, and any air-bubbles are carefully removed. 2. The stoppered weighing bottle, completely filled (to exclude air) with the known weight of the substance to be experimented on, is placed upon the mercury in the measuring-tube, and the rubber stopper, fitted with the N-tube, is forced into the neck. The weighing-bottle is thus forced inwards, causing the excess of mercury to fill the N-tube and some to escape (Fig. 4). The stopper should be tied on to the lip round the neck of the measuringtube with a little soft wire.

3. The whole is now inverted. If the weighing-bottle does not rise upwards, gentle tapping on the tube-wall will cause it to do so.

4. The tube is next surrounded with a suitable heating jacket, and heated in the vapour of some liquid boiling at a temperature above that at which the substance vaporises at ordinary atmospheric pressures (Fig. 5).

5. When the volume of the vapour in the measuring-tube remains constant, the position of the mercury-meniscus is noted, and the difference in height, m, measured in mm., between the mercury levels in the N-tube and measuringtube is measured.

6. The measuring-tube is removed, emptied of mercury, and, without removing the weighing-bottle, water is poured in from a burette to reach the position the mercury occupied; the volume, v, of the water represents the volume of the vapour.

7. The atmospheric pressure, p, measured in mm., and the heating temperature, to, are required known.

8. w is the weight of the substance experimented on.

Theory.

The volume of the vapour reduced to o° C. and 760 mm. pressure

=

273(p+m)v

760 (273 +t)

;

and the density of the vapour is therefore this quantity divided into w; or, the vapour density, compared with hydrogen at o° C. and 760 mm. pressure (taking that

*The author's descriptions of "A Simple Method for Determining Vapour-densities and for Analysing Binary Mixtures" in the CHEMICAL NEWS, 1909, c., 13, 129, 174, have met with such favour that he has yielded to several requests to compile this complete summary of his rather scattered papers upon the above mentioned subject which appeared in the Berichte, 1908, xli., 768, 881, 1588, 2487, 4141; and Journal of Physical Chemistry, 1908, vii., 679; xiii., 433.

=

d =

11160 × 760 w (273+t)

273 (pm) v

(the formula to be used in practice)—

31068 w (273+t). (p±m) v

A, The weighing bottle. B, Transverse section of the measuringtube, with the weighing-bottle lying on the mercury.

Precautions and Observations.

the various quantities, no difficulty should be found in 1. If every precaution be taken to measure accurately obtaining results practically in accordance with the required theoretical values.

2. A successful experiment should occupy forty-five to sixty minutes.

3. When any substance, other than steam, be used as the heating medium it should be recovered by means of a suitable condenser and receiver in proper connection with the heating jacket.

4. If the N-tube be replaced by a short U-tube, and a long wide glass tube attached to it by aid of a short thick piece of rubber pressure tubing, mercury can be poured in so as to vary m (Fig. 6).

5. Still greater advantage will be obtained, though rather more difficulty in manipulation may be encountered, if the N-tube or U-tube be originally replaced by a straight tube, and joined on to a long wide glass tube by means of a thick rubber pressure tubing, when very great variations in m (m) can then be effected (Fig. 7).

6. If the measuring-tube be properly graduated in cc. and tenths cc. (from the closed end), the volume of the vapour (less the volume of the weighing-bottle) can be read

NEWS

the curvature of the mercury-meniscus and for the expansions of the glass tube and mercury.

10. It is possible that through want of sufficient care a few air-bubbles may be found in the measuring-tube after it has been fitted up ready for heating. This does not at all necessitate the repetition of the operations. The tube is tapped slightly to cause all these air-bubbles to rise to the top; the position of the mercury meniscus is noted, so that, at the end of the experiment, the volume (v1) of this air can be determined (allowing, of course, i.e., minus, the volume of the weighing-bottle), or if the tube be graduated this quantity (vi) can be read directly; at the same time, the difference in height, mi, measured in mm., between

off directly, and thus a troublesome operation may be avoided. (Messrs. F. E. Becker supply these graduated tubes).

7. By using the modification in Precaution 5 it is possible, by sufficiently reducing the pressure (i.e., by making ma sufficiently large minus quantity), to vaporise substances at temperatures far below the temperatures at which they vaporise at ordinary pressures.

8. It is best to have a thermometer suspended within the heating jacket to indicate the exact vaporising temperature.

9. For very accurate work allowance must be made for

FIG. 7.

the mercury-levels in the tubes is measured, and the room temperature, t° C., and atmospheric pressure, pi, measured in mm., are determined.

The calculation is then effected by means of the final formula here shown derived :

Let w the weight of the substance;

=

=

P2 the atmospheric pressure, measured in mm., at the end of the experiment (generally p1=P2);

m2= the difference in height between the mercurylevels when the substance has been vaporised (measured in mm.);

v2 = the combined volume of the air and vapour; = the temperature of the vapour.

t2°

(pi±mi)vi (273 +t2)

(P2 ± m2) (273 +tı)

;

A Study of some Reactions of Tellurium, Selenium, with Special Reference to the Tellurium Minerals. Tellurium and Gold Solutions.-In 1828, N. W. Fischer (Pogg. Annal., xii., 502) found that tellurium reduces the salts of gold, silver, platinum, and palladium, when introduced into their solutions. He considered the reduction as incomplete in all cases, but that the reaction of gold solutions was the most rapid, the reaction in this case being stopped by the tellurium becoming coated with metallic gold, which prevented further action, even at high temperature. It has been found (Lenher, Journ. Am. Chem. Soc., xxiv., 355) that when metallic tellurium is treated with a chloride of gold solution, metallic gold is deposited according to the equation 4AuCl3 +3Te=4Au+3TeCl4. The reaction is greatly accelerated by warming the solution, and if the gold chloride is in excess, and sufficient time is allowed, the tellurium completely passes into the solution, leaving fine gold as a precipitate. On the other hand, if tellurium is introduced into a gold chloride solution in greater quantity than that necessary to precipitate all of the gold, the yellow gold solution will soon become completely bleached, and on examination will be found to contain no gold. The action of the tellurium on the gold solution is fairly rapid; warming the solution a few minutes will bring down sufficient gold to colour the tellurium yellow, but in order to insure a complete reaction two or three hours continuous heating are necessary, or several days contact at room temperature. In order to obviate the difficulty of incomplete reduction noted by Fischer, it is only necessary to reduce the tellurium to a fine state of division and allow a sufficient time for reaction. When such conditions are fulfilled, the deposition. of metallic gold by elementary tellurium is quantitative from either acid, neutral, or alkaline solution.

Tellurium and Silver Solutions.-The reaction (Hall and Lenher, Journ. Am. Chem. Soc., xxiv., 918) between silver salts and elementary tellurium results in the formation of silver telluride. Silver nitrate solution in contact with elementary tellurium which has been reduced to a fine state of division will in eight or ten days yield silver telluride according to the equation

* From Economic Geology, 1909, iv., No. 6.

123

4AgNO3+3Te = 2Ag2Te+Te(NO3)4. The reaction proceeds more rapidly if the solution is kept boiling or is maintained at a temperature of 80°. Silver chloride dissolved in ammonia will on contact with tellurium produce silver telluride thus: 4AgCl + 3Te = 2Ag2Te+TeCl4.

In studying these reactions in ammoniacal solution it has been observed that if silver nitrate dissolved in ammonia is allowed to stand for several days, or if the solution is kept warm for a considerable length of time, a black deposit which is probably a nitride of silver separates out. When silver chloride in ammonia is used in this reaction an excess of ammonia is desirable, and the reaction is best carried out at room temperature. With silver nitrate in aqueous solution a greater range of temperature is possible; in fact, the solution can be boiled continuously. The resultant precipitate, if extracted several times with ammonia, will lose any silver telluride held mechanically or formed in the reaction. With due regard to the above precautions it is possible to obtain a good preparation of silver telluride by the action of elementary tellurium on silver solutions.

Selenium and Gold Solutions.-Pure selenium acts with gold solutions in a manner similar to that of tellurium, the reaction being, however, very much moderated. The fused variety of selenium does not reduce gold at the ordinary temperature. Indeed, one experiment was made allowing the selenium to remain in contact with the gold solution for three months without visible change. At the boiling temperature the reaction proceeds nearly as rapidly as with tellurium, and takes place in a perfectly analogous manner, the reaction being expressed, 3Se+4AuCl3 = 3SeCl4 +4Au. In order to secure complete action it is necessary that the selenium shall be in a fine state of division, and that sufficient time shall be allowed in order that complete contact may be assured. It is necessary for the solution of the gold to be boiled with the seleniumi for six to eight hours, or the gold solution should be allowed to be in contact with the selenium for two or three days at from 70° to 80°. The reaction then between selenium and gold solutions results in the quantitative precipitation of metallic gold.

Selenium and Silver Solutions.-Parkham (Chem. Cent., xxxiii., 813) observed that red selenium is blackened in a solution of silver nitrate, selenious acid being formed at the same time; after the latter had been removed by sodium hydroxide, the black powder remaining contained selenium and silver, but no unchanged selenium could be detected with the microscope. Senderens (Comptes Rendus, civ., 175) found that selenium would reduce a boiling solution of silver nitrate, either dilute or concentrated, with the formation of silver selenide and selenium dioxide. The statement of Parkham is obviously in error in regard to a precipitate of selenium dioxide in aqueous solution inasmuch as selenium dioxide is really soluble in water.

The action of selenium on silver solutions is quite similar to that of tellurium, but is not as energetic. Selenium reduces solutions of silver nitrate or of the chloride in ammonia, either in the cold or on heating, with formation of silver selenide. As might be expected the reaction is materially accelerated by heat.

Reaction of Tellurium Minerals with Gold Solutions.The tellurium gold minerals, calaverite, hessite, nagyagite, as well as native tellurium, all precipitate metallic gold from a solution of the chloride. In fact, they deport themselves toward gold solutions precisely as elementary tellurium does. When the tellurium mineral is in excess the yellow-gold solution is bleached to a colourless solution which contains no gold, while if the gold chloride is in excess, the amount of gold precipitated is in proportion to the quantity of tellurium and selenium present.

It is obvious that these natural tellurides act toward gold solutions unlike chemical compounds of gold and tellurium, since we know of no true chemical compound that can precipitate one of its constituents in such a manner as takes place with the natural tellurides and gold

solutions.

(To be continued).

PROCEEDINGS OF SOCIETIES.

CHEMICAL SOCIETY.

Ordinary Meeting, March 3rd, 1910.

Prof. HAROLD B. DIXON, M.A., F.R.S., President
in the Chair.

MESSRS. A. J. Child, R. H. Cocks, H. H. Hughes, L. C. W. Jenkins, and H. W. Southgate were formally admitted Fellows of the Society.

Certificates were read for the first time in favour of Messrs. Oscar Lisle Brady, B.A., 51, Upper Bedford Place, W.C.; Henry Leslie Farmer Buswell, B.A., 169, Queen's Gate, S.W.; Thomas Patrick Cheetham, Vrijheid, Natal, S.A.; Thomas William Dickson, B.A., 153, Finborough Road, South Kensington, S.W.; Harold Albert Goldsbrough, Churchside, Herne Hill, S.E.; James Kenner, Ph.D., B.Sc., 61, Marlborough Road, Sheffield; Sea-Kwain Kwoh, 125, Acomb Street, Manchester; Samuel Lamb, May Villa, Birmingham Road, West Bromwich ; Knowles Preston, Newhaven, Camden Avenue, Feltham, Middlesex.

Certificates have been authorised by the Council for presentation to Ballot under By-law I. (3) in favour of Messrs. Georges Baume, 44, Quai des Eaux, Vive, Geneva; Motilal Kashalchand Shah, Byculla Bridge, Byculla, Bombay.

The PRESIDENT read the names of the Fellows recommended by the Council for Election as Officers and Ordinary Members of Council of the Society.

DISCUSSION.

Mr. MARSH, in reply to Mr. Carr, said that the salt 2KI+HgI2 did not bring about the miscibility of ether and water to the same extent as the salt KI+HgI2, nor was the effect of change of temperature so marked.

*55. "The Relation between Absorption Spectra and Chemical Constitution. Part XIV. The Aromatic Nitrocompounds and the Quinonoid Theory." By EDWARD EFFIE GWENDOLINE MARSDEN. CHARLES CYRIL BALY, WILLIAM BRADSHAW TUCK, and

It has been proved (Trans., 1908, xciii., 1747) that the nitro-group possesses a free period of vibration, and it follows that if in any compound the nitro-group is in conjunction with a system which also has a free period of vibration, the substance will show an absorption band arising from the isorropesis which takes place. Such compounds are to be found in the substituted nitrobenzenes, where the substituent groups are of the so-called positive type. For example, the nitronaphthalenes, nitrofluorene, and nitroquinol dimethyl ether all show wellmarked absorption bands. The position of the absorption bands depends on the position of the band of the group in conjunction with the nitro-group. The results described throw some doubt on the validity of the quinonoid theory, strong evidence being obtained from the nitrodimethylanilines and the nitrobenzylideneanilines. The position of the absorption band in the nitro-compounds is found to vary with the residual affinity of the solvent. An increase in the residual affinity causes a shift in the band towards the red.

DISCUSSION.

Of the following papers, those marked were read:*54. "Phenomena observed when Potassium Mercuriiodide is Dissolved in Ether and Water." By JAMES ERNEST MARSH.

The salt KI,HgI2, H2O dissolves in ether with evolution of heat, and this solution dissolves water with a further evolution of heat. On the other hand, water acts on the double salt with absorption of heat and with separation of part of the mercuric iodide; the addition of ether to this mixture brings about complete solution with evolution of heat.

A solution of one molecular proportion of potassium and mercuric iodides in seventeen molecular proportions of ether and water separates, on warming, into three layers. As the temperaure rises, the middle layer gradually diminishes in quantity and disappears. On cooling, the middle layer reappears again, and increasing in quantity as the temperature falls, eventually absorbs the other two.

A solution of less concentration than the above gives, on warming, two layers, the upper one increasing as the temperature rises, and being re-absorbed as the temperature falls. With a solution of greater concentration, two layers are also formed on warming, but in this case it is the lower layer which increases with the temperature, and is re-absorbed on cooling.

When potassium iodide and mercuric iodide in molecular proportions are dissolved in cold ether with the addition of sufficient water to form the double salt KI,HgI2, H2O, the latter crystallises on warming the solution, but re-dissolves on cooling.

In dry ether the two salts dissolve, forming a heavy liquid of the composition KI,HgI2,4Et2O, which does not appreciably dissolve in excess of ether.

was by no means improbable.

Dr. LowRY said that he was able to confirm from his own observations the migration of a band towards the visible region on displacing hydrogen by sodium, and in the opposite direction on displacing hydrogen by acetyl, and also the identity of the spectra of compounds containing the radicles NH2 and OÑa; but he did not believe that the nitro-group was capable of producing an absorption band except when acting in conjunction with other unsaturated groups. Such groups were present in nitrobenzene and in nitrostyrene, but not in nitromethane or in nitroethane; the latter compounds were, however, very unstable, and the bands (which were not produced by nitrocamphane) might be attributed to decomposition products,

The quinonoid formula for sodium o-hydroxycinnamate did not necessarily involve the attachment of sodium to carbon, as the compound might be written :O:C6H4:CH CH:C(ON)2.

Dr. MORGAN said that one interesting point in the paper which had not been referred to by previous speakers was the fact, demonstrated by the authors, that the aromatic meta-nitroamines had absorption spectra quite similar to their ortho- and para-isomerides, even when, as in the case of 2-nitrodimethyl-p-toluidine, the migration of a labile hydrogen atom could not take place. The colour of these meta-nitroamines was often more intense than that of their ortho- and para-isomerides, and this circumstance negatived the view that the colour of the ortho- and para-series was due to the existence in these compounds of ortho- and