CHEMICAL NEWS,

March 31, 1911

Determination.

149

Standard Method No. 1.-The filtrate from the suspended impurities determination (including the hot petroleum ether washings) is evaporated to a bulk of about 200 cc., and allowed to stand over night or twelve hours in a cool place (18-20° C.). It is then filtered from the separated insoluble metallic soaps on a Gooch crucible, washed with cold petroleum ether (boiling-point 35-50° C.), dried, and weighed.

Standard Method No. 2.-The filtrate from the suspended impurities determination is evaporated, burned, and ignited to constant weight. (a) The weight of the ash from metallic soaps thus obtained is to be reported as such. (b) Considering the ash to consist entirely of calcium oxide, it is to be calculated to normal soap, using 281 as molecular weight of fatty acid and reported as lime soap.-Journal of Industrial and Engineering Chemistry, iii., No. 1.

6. Unsaponifiable Matter. Definition. The non-fatty acid constituents of fats and fatty oils, soluble in petroleum ether (boiling-point 35° to 50° C.).

Determination.

Standard Wet Method.-Three grms. of the sample, free from moisture and volatile matter, are weighed into a 150 cc. flask, and a 30 per cent excess of strong colourless or nearly colourless alcoholic potash solution added. The contents are boiled for one hour under a reflux condenser, and then transferred to a stoppered 100 or 150 cc. cylinder and made up to 50 cc. with cold water. Add 30 cc. of re-distilled petroleum ether (boiling point 35-50° C.), and agitate vigorously. Draw off the petroleum ether layer by means of slender glass syphon. Repeat this operation with five separate portions of petroleum ether. Place the 150 cc. of petroleum ether into a Squibb's pear-shaped separatory funnel (250 cc.), and wash three times with 20 cc. of 50 per cent alcohol. Pour the contents of the funnel into a tared flask, and distil off the greater part of the petroleum ether and complete the drying on a steambath and in an oven, the latter held below 105° C.

Standard Dry Method.-Approximately 5 grms. of fat or oil are weighed into a 200 cc. capacity Soxhlet or Erlenmeyer flask, and saponified with sufficient alcoholic sodium hydrate solution to give 50 per cent excess of sodium hydrate by boiling under a reflux condenser for half-an-hour to one hour or until saponification is complete. The solution is then transferred to a 4-inch porcelain evaporating dish (the flask being rinsed with hot alcohol) and dried on a water-bath. The drying is completed in the oven at 120° C. for one to two hours. Grind the dried soap in an agate mortar with 10-15 grms. granular an hydrous sodium carbonate, and place the whole in a 33 x 80 mm. S. and S. extraction thimble, using a fat-free plug of cotton to cover the charge. Place the thimble and contents in oven, and re-dry for one hour at 110-120° C. The extraction is made with re-distilled light petroleum ether boiling from 35-50° C. During the extraction if a Soxhlet or Knorr apparatus is used the open end of condenser must be protected against atmospheric moisture by a CaCl2 tube. All connections of the apparatus must be tight. The extraction is allowed to proceed for about ten hours (if a Soxhlet apparatus is used at least 50 discharges). Transfer the extract to a weighed beaker, evaporate solvent on the water-bath and dry in an oven to constant weight. Test the extract by re-dissolving in light petroleum ether; a clear solution should be obtained if the determination has been properly carried out.

7. Metallic Soaps. Definition. The insoluble metallic soaps in the present sense are the fatty acid compounds of bases other than the alkalies. They are insoluble in water.

STRUCTURE.*

By Prof. WILLIAM J. POPE, M.A., F.R.S

LARGE numbers of chemical substances occur on the earth's surface as definite geometrical forms bounded by plane faces; these polyhedral shapes are called crystals. Inspection of the crystal forms assumed by mineral substances shows that, roughly speaking, each crystalline substance affects some specific geometrical shape which is characteristic for the material; further that, whilst crystals of any particular mineral attain vastly different dimensions and are bounded by planes which vary greatly in relative area, one geometrical feature remains constant. The angles between corresponding pairs of faces on any two crystals of the same substance are the same, notwithstanding the existence of difference in size, or in relative face magnitude between the two crystals. The constancy of interfacial angle amongst crystals of the same substance is a law of nature, and has been amply demonstrated by the very careful crystallographic measurements made by Tutton during the last twenty years.

It is, however, not essential to study mineral substances alone in order to obtain a knowledge of the laws governing crystal growth. Great numbers of laboratory products can be caused to crystallise by condensation from some fluid condition; thus, the crystals of various alums exhibited were obtained by slow evaporation of aqueous solutions of these salts.

The examination of a crystal shows that many of its physical properties differ according to the direction in the crystal in which the property is determined; the hardness of crystals, the speed at which light travels through them, and many other properties, are commonly dependent on the direction in which the material is examined.

The dependence of crystal properties on direction indicates the most essential feature of the crystal to be a definite and orderly arrangement of its ultimate particles; this arrangement is referred to as the crystal structure. Further evidence that crystals possess an arranged structure is furnished by the observation that crystallisation is not necessarily a spontaneous process. Thus, on melting benzophenone and rapidly cooling the clear molten mass, the liquid state is retained for many hours at a temperature far below the normal melting point of the compound. But on inoculating the liquid with a trace of crystalline benzophenone crystallisation immediately commences and rapidly becomes complete. The introduction of a small particle of crystalline or arranged material into the liquid mass provides a hucleus upon which the molecules are able to deposit themselves in a similar crystalline arrangement; the process thus started quickly becomes propagated throughout

Many substances are capable of crystallising in two or more distinct crystalline forms of which one is, in general the more stable at any particular temperature. The physical properties of the several crystalline modifications of any one substance are quite distinct and characteristic for the particular crystalline form and, in many instances, even the colours of the several modifications are different. An example of this is afforded by pouring boiling water into a beaker coated with cuprous mercuric iodide; the brilliant scarlet crystalline form stable at ordinary temperatures, when heated in this way, becomes converted into another crystalline modification which is nearly black. The change is a reversible one, and the differences between the properties of the two crystalline modifications are to be attributed to differences in the mode of arrangement of the molecules in the two cases; the two modifications, in fact, possess different crystalline structures.

Although vast numbers of observations, such as the preceding, lead to the conclusion that crystals are arranged structures, it is not essential that the crystal should be a solid substance; during recent years large numbers of crystalline liquids have been discovered. On allowing melted cholesteryl chloride to cool rapidly a brilliant display of interference colours is seen, owing to the particles of the substance assuming crystalline or orderly arrangement whilst still retaining the liquid condition.

Having very briefly reviewed some of the many reasons for concluding that crystals are structured edifices, the nature of the architecture which they exhibit may now be considered. All the properties of crystalline solids harmonise with one simple assumption as to the manner in which the parts of the structure are arranged; this assumption is that the structure is a geometrically "homogeneous" one,| that is, a structure the parts of which are uniformly repeated throughout, corresponding points having a similar environment everywhere within the edifice. The assumption of geometrical homogeneity as the characteristic of crystalline solids leads at once to the great problem solved by the crystallographers of the nineteenth century. This consisted in the inquiry as to how many types of homogeneous arrangement of points in space are possible, to the study of those types and to their identification, in symmetry and other respects, with the known systems into which crystalline solids fall. This work was commenced by the German crystallographer Frankenheim in 1830, and completed by the English geometrician Barlow in 1894. Briefly stated, the final conclusion has been attained that 230 geometrically homogeneous modes exist of distributing material, or points representing material throughout space, and that these 230 homogeneous types of structure, the so-called homogeneous "point-systems," fall into the 32 types of symmetry exhibited by crystalline solids. Models of a number of homogeneous point systems illustrating some of these types are exhibited.

It is, however, obvious that the limitation of the possibilities of solid crystalline arrangement to 230 types marks but one stage in the determination of the nature of crystal structure, and throws no direct light on the relation between crystal structure and chemical constitution.

learnt that corresponding points of the units of crystalline structures form homogeneous point-systems, the great problem still remained of determining what are the entities which become homogeneously arranged, for what reason they become so arranged, and in what way the conclusions drawn by modern chemistry are reflected in crystal structure. This problem was a legacy to the twentieth century, and it now remains to indicate briefly the extent to which it has been solved and the results of chemical importance which have accrued during its investigation. The problem may be most easily visualised in connection with some comparatively simple case, that, for instance, presented by the crystalline forms assumed by the elements themselves. It is generally admitted that an elementary substance consists of identical atoms, each of which acts as a centre of operation of attractive and repulsive forces. In a solid crystalline structure the atoms are obviously not free to travel through the mass, each, if not indeed fixed to a particular spot, being retained within a certain minute domain; each of these domains must be regarded as possessing a centre which marks the mean position of the atom.

The crystalline condition of an element may consequently be defined as one of equilibrium between forces of attraction and repulsion emanating from or referable to a flock of points homogeneously arranged in space, that is to say, of points of a homogeneous point-system. Under these conditions, the space occupied by a crystalline element, a homogeneous assemblage of identically similar atoms, may be partitioned into identically similar cells in such a manner that the boundaries of a single cell shall enclose the entire domain throughout which a particular atom exercises predominant influence. Since it is postulated that every point in the space is subject to the dominating influence of some next neighbouring atomic centre, it follows that the cells fit together so as to occupy the whole available space without interstices. Nothing is here said about the shape of the cells; but since, in the case of an elementary substance, the atomic centres are all alike, so too will be the cells. Before proceeding to discuss the actual shapes of the cells referred to, it will be convenient to illustrate more graphically the mode of treating the problem which is here introduced with the aid of a particular point-system connected with the crystalline structure of elementary substances.

The point-system in question may be derived in the following manner. Space is first partitioned into cubes by three sets of parallel planes at right-angles to one another (Fig. 1); a point is then placed at each cube corner and at the centre of each cube face. The cubes of the partitioning, having served their purpose, may now be removed, leaving one of the 230 types of homogeneous point-systems (Fig. 2). Imagine next that each point of the system expands uniformly in all directions until it touches its neighbours a system of spheres packed together in contact is thus obtained (Fig. 3), and, on examination, it is found that no way exists of packing these equal spheres more closely together than the one thus derived. The system is therefore termed the 'cubic closest-packed assemblage of equal spheres and, being derived in the manner described, still retains the high symmetry of the cube; the fragment shown, in fact, outlines a cube. Three directions at right angles in it, those which are parallel to the three cube edges, are seen to be identical in kind; this identity in kind in the three rectangular directions, a, b, and c, is conveniently expressed by the ratio, a: b c = 1: 1: 1.

On removing spheres from one corner of the cubic closestpacked assemblage of equal spheres a close triangularly arranged layer is disclosed, and, by similarly treating each corner of the fragment of assemblage, the cube outline gives place to one of octahedral form. The assemblage is now seen to be built up by the superposition of the disclosed triangularly arranged layers, the hollows in one layer serving to accommodate the projecting parts of the spheres in adjacent layers. When this operation is per

The final step in the treatment of the closest-packed assemblages of equal spheres consists in converting them into the corresponding assemblages of cells fitting together without interstices which have been already mentioned; it may be carried out in these, and in all other cases, by causing the component spheres to expand uniformly in all directions until expansion is checked by contact with the expanding parts of neighbouring spheres. The cubic closest-packed assemblage then becomes a stack of twelvesided polyhedra, rhombic dodecahedra, which are so fitted together as to fill space without interstices. It is now seen that the even rate of expansion from each point of the original point-system which gives rise to the closely packed stack of rhombic dodecahedra, symbolises an even radiation in all directions of the forces of which the atom is the centre of emanation. On applying the same operation of expansion to the spheres present in hexagonal closest-packing, each becomes converted into a dodecahedron, although of symmetry different from that of the rhombic dodecahedron. In each of the two cases the system exhibits the important property that, with a given density of distribution of the centres, a maximum distance prevails between nearest centres; these two systems thus represent the equilibrium arrangements of the postulated forces of repulsion exerted between near centres, the repulsions between more distant ones being neglected.

It will be sufficiently evident from what has been said that the function of the spherical surfaces in the closest packed assemblages of spheres, as representing crystal structures, is merely a geometrical one; these surfaces are employed only as so much scaffolding by the aid of which may be derived arrangements exhibiting a maximum number of equal distances between neighbouring centres, and no physical distinction is to be made between portions of space lying within the spheres and portions forming part of the interstices between them. Insistance on this point is necessary, because many investigators have made use, quite illegitimately, of spheres for the representation of atomic domains, piling the spheres together in what they have termed open packing; this term seems to imply that some physical difference can subsist between the portions of space lying within the spheres and those lying without. The one kind of space is apparently regarded as susceptible to atomic influence in some sense not exhibited by the other. To state this view in any definite manner probably suffices to demonstrate its superficiality; the question of ascertaining what proportion of the total space is available for atomic occupation by the use of assemblages of spheres does not arise because the spheres used are solely the geometrical instruments for producing equality amongst the atomic distances, and so determining the prevailing equilibrium conditions.

So far as the enquiry has been carried, it would seem that the elements should crystallise either in the cubic or the hexagonal system, and that in the latter case corresponding dimensions in the horizontal and vertical directions should be in the ratio of a: c = 1:08165. The facts are summarised in Table I.

Of the elements which have been crystallographically examined, 50 per cent are cubic; their crystal structure is simulated by the cubic closest-packed assemblage of equal spheres. Another 35 per cent belong to the hexagonal system, and that these are correctly represented by the hexagonal closest-packed assemblage of equal spheres is indicated by the fact that for the hexagonal elements the ratio of corresponding dimensions in the horizonal and vertical directions approximate to the value a : c = 1:0·8165, deduced for the model assemblage.

The task of accounting for the 15 per cent of the crystal line elements which have been examined and found to crystallise in systems other than the cubic or hexagonal still remains. A little inspection shows that the crystal

Cubic..

Complexity.

50

Number of atoms in molecules of compound inorganic substances. Organic More pounds 5. than 5. 68.5 42 5 12

com

5.8

2.5

Hexagonal
Tetragonal
Orthorhombic
Monosymmetric
Anorthic

Number of cases summarised in each vertical column ..

(The proportion of substances crystallising in each system is stated above as a percentage).

=

forms of these elements in every case approach very closely to one or other of the two of highest symmetry, namely, the cubic or the hexagonal; one example of this will now suffice. The values of corresponding dimensions in three directions in space for the monosymmetric form of the element sulphur are given by the axial ratios a : b : c~ 0.9958: I: 0.9998, 95° 46'. The slight departure of these dimensions from the corresponding values for the cubic closest-packed assemblage, in which a:b: c = 1 : 1 : 1, 8- 90°, at once suggests that the monosymmetric modification of sulphur is derived from the latter assemblage by some minute distortion. Such a distortion indicates a very trifling departure from uniformity in the influence exerted in different directions from each atomic centre, and may either arise from some want of symmetry in the individual atoms, or in a reduction of the symmetry caused by some grouping of the atoms; two or more atoms might thus be more closely connected in some way with one another than with other next neighbouring atoms.

(To be continued).

PROCEEDINGS OF SOCIETIES.

ROYAL SOCIETY.
Ordinary Meeting, March 9th, 1911.

Sir ARCHIBALD Geikie, K.C.B., President, in the Chair.
PAPERS were read as follows:-

Absorption Spectra of Lithium and Casium." By Prof. P. V. BEVAN.

This paper gives an account of the continuation of work done on the absorption spectra of vapours of the alkali metals. Difficulty was found in obtaining tubes which were not acted on by lithium vapour, and this difficulty was never completely surmounted. By the use, however, of considerable quantity of lithium in a steel tube the absorption spectrum was obtained, and twenty-seven lines of the principal series were observed. The measurements for the whole series are given in the paper, the lines from the tenth to the twenty-seventh being new. The paper further gives measurements of wave-lengths for the similar lines for cæsium. The series has been extended to include twenty-four lines, and re-measurements were made as there was pointed out by Prof. Hicks some probable errors in former determinations. The two series for lithium and, cæsium are compared with the formulæ suggested by Hicks, and it is found that the agreement of calculated and observed wave-lengths is exceedingly good, a slight change in one of the constants for cæsium being indicated.

Prof. P. V. BEVAN.

This paper gives an account of measurements of the dispersion in rubidium and sodium vapours. The work is of the same character as that on the dispersion in potassium vapour described in the Proceedings of the Royal Society, 1910, A, lxxxiv. Dispersion curves for the rubidium vapour were obtained for the region of wave-lengths 6000 to 3000. Anomalous dispersion effects were observable at the first eight members of the principal series lines. These lines being pairs, interesting curves are obtained for the second and third pairs. stants in the Maxwell-Sellmeier formula are obtained, and similar conclusions drawn from them as in the case of the paper already referred to concerning the numbers of atoms taking part in the absorption of light. Measurements of wave-lengths of the lines of the principal series are given, and these are shown to be in good agreement with the values calculated from the Hicks modification of the Rydberg formula. Similar measurements were made in the case of sodium. In this case the effects are not so large or so easily obtainable as in the cases of rubidium and potassium. Measurements were also made to see it any temperature effect could be detected in the ratios of the constants of the dispersion formula. These go to show that the ratios m1/m2, m2/m3, &c., where m1/m2, &c., are the constants corresponding to the first, second, &c., lines of the principal series, increase with increase of temperature. This result is what might be expected if the absorbing atoms are ordinary atoms to which corpuscles become attached, more complex systems corresponding to higher members of the series of lines in the spectrum.

The relative values of the con

"Ionic Solubility Product." By J. KENDALL, B.Sc. Previous investigations upon the simultaneous solubility in water of two substances containing a common ion have been confined to those cases in which the substances examined have been of the same type-i.e., either both strong or both weak electrolytes. In each case the experimental results have been considered to be consistent with

the hypothesis of a constant ionic solubility product, although, even in dilute solutions, the agreement is only approximate.

The primary object of this research was to test the applicability of the theory to substances of opposite types, one strong and one weak electrolyte. Preliminary experiments showed that here also small divergences were obtained. Finally, a series of experiments on all the possible types of combination of two electrolytes was carried out, first with dilute and afterwards with more concentrated solutions, in order to ascertain the cause of these divergences and their bearing upon the solidity of the theory,

The results obtained show that the mutual solvent actions of the two substances play an important part in the equilibrium. The general rule appears to be that two substances chemically similar in character give results in excess of theoretical, while with two chemically dissimilar a diminution is observed. In dilute solutions all divergences are small, but fundamental, and in certain cases the amount due to each of the two substances is calculated. In the more concentrated solutions, where the solvent effect is greater, the three possible types of solubility curves are obtained and discussed, and it is found that in all cases experimental divergences from values indicated by the constant solubility product hypothesis can be fully accounted for by this solvent effect of the substances upon each other.

"Note on the Electrical Waves occurring in Nature." By W. H. ECCLES, D.Sc., and H. MORRIS-AIREY, M.Sc. The occurrence of a lightning stroke must, in general, give rise to either a solitary electric wave or a train of electric waves which will be propagated from the centre of discharge to unknown distances. These vagrant waves join with other natural electric phenomena to cause disturbances-technically called "atmospherics" in the

153

receiving circuits of wireless telegraph stations. Among these other phenomena may be mentioned charged hail or rain striking the air-wires, and earth-air currents. The present communication describes an endeavour to determine the proportion of atmospherics of distant origin.

The plan of attack was as follows:-One of the authors in London and the other in Newcastle arranged receiving apparatus just as for the telephonic reception of signals. and simultaneously listened, at pre-arranged times, for atmospherics. A hand record of the time and intensity of each strong atmospheric was made on paper ruled to represent ten seconds of time per inch. By arranging the periods of observation to include the midnight time signals from the Eiffel Tower or from Norddeich, the time records of the two observers could be accurately co-ordinated. The observers exchanged copies of their records, and counted the number of marks coinciding in time. The results tend to show that about 70 per cent of the atmospherics audible at two stations 270 miles apart, are due to vagrant waves propagated from electrical discharges that take place at (possibly) very great distances.

"Action of Animal Extracts on Milk Secretion." By Prof. A. E. SCHÄFER, F.R.S., and K. MACKENZIE.

Ordinary Meeting, March 16th, 1910.

Sir ARCHIBALD Geikie, K.C.B., President, in the Chair. PAPERS were read as follows:

"Gametogenesis of the Gall-fly (Neuroterus lenticularis)." (Part II.). By L. DONCASTER, M.A., Fellow of King's College, Cambridge.

"Action of the Venom of Echis carinatus." By Sir THOMAS R. FRASER, M.D., F.R.S., and Jas. A. Gunn, M.A., M.D.

"Further Researches on the Development of Trypanosoma gambiense in Glossina palpalis." By Colonel Sir DAVID BRUCE, C.B., F.R.S., A.M.S.,; Capts. A. E. HAMERTON, D.S.O., and H. R. BATEMAN, R.A.M.C.; and Capt. F. P. MACKIE, I.M.S. (Sleeping Sickness Commission of the Royal Society, Uganda, 1908-10). M.D., Imperial Cancer Research Fund. "Spontaneous Cancer in Mice." By M. HAALAND,

FARADAY SOCIETY.

Ordinary Meeting, March 14th, 1911.

Dr. J. A. HARKER, F.R.S., in the Chair.

A PAPER ON "Some Properties of Aluminium Anode Films,” by G. E. BAIRSTO, M.Sc., B.Eng., and R. MERCER, B.Eng., was read in abstract by the Secretary.

This paper gives a preliminary account of an extended investigation that is being made into some of the properties of aluminium anode-films, with special reference to the capacity of such films, and to their behaviour in several electrolytes that have not, previous to this, been used to

"form" them.

1. The differences found in the results of previous observers for the capacity of Al anodes are explained by the experimental difficulties involved in messuring the capacity of a very leaky condenser, and by the influence of the length of the period of formation.

Using Sumpner and Record's very accurate method of adapting a Sumpner wattmeter to the measurement of capacity, it was found that the capacity decreases slowly with the time of formation for several days. The higher the formation voltage, the longer is the time required for the capacity to fall to its minimum value. The product of the capacity per sq. cm. and the formation voltage is not constant, but decreases with E, ranging from 8.1 to 6.9