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All applications for space to be made to H. A. COLLINS, 32 Birdhurst Road, Croydon. THE LONDON, EDINBURGH, AND DUBLIN PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. [SIXTH SERIES.] JUNE 1918. LIII. Molecular Frequency and Molecular Number. — Part III. Inorganic Compounds. Lindemann's Formula. By H. STANLEY ALLEN, M.A, D.Sc., University of London, King's College*. IN N the present communication are given the values of the characteristic molecular frequency, v, calculated by Lindemann's formula for those inorganic compounds for which data are available. The formula in question may written v=k be where T, is the absolute temperature of the melting-point, M is the molecular weight, and V the molecular volume. The coefficient k has been assumed constant, and Nernst's empirical value, 3.08 × 1012, has been employed. For each compound is tabulated the value of the molecular number, N, and of the product Nv x 10-12. In the majority of cases it has been found possible to express No either in the form av or in the form (+), where n is an integer and v is a constant frequency having a value about 21 x 1012 sec.-1. In the few exceptional cases where neither of the above forms is applicable the product has been expressed as (n + 1) v or (n+v, but no special significance is at present attached to such results. All the results here given must be considered in the light of the general considerations affecting Lindemann's formula put forward in Part I. of this papert. * Communicated by the Author. † Phil. Mag. vol. xxxv. p. 338, April 1918. Phil. Mag. S. 6. Vol. 35. No. 210. June 1918. 2 I Compounds containing water of crystallization have not been included, as in such cases it is often difficult to decide whether the recorded temperature is a true melting-point or the temperature at which the solid dissolves in the water of crystallization. GROUP I. Of inorganic compounds for which the density and the melting-point are known, a larger proportion belongs to the first group than to any other group in the Periodic Table. With a small number of exceptional or doubtful cases, the results show good agreement with the suggested relations. It is noteworthy that when the temperature of the melting-point is known accurately, the agreement is better than when this temperature is uncertain. VA For several of the lithium compounds the melting-point has not been determined with great accuracy, yet the values of v do not differ widely from the mean value which is 20.7 x 1012 sec.-1 The mean value for the elements, given in a former paper*, was 20.9 × 1012 sec.-1, when the same factor was employed in Lindemann's formula as that here used. It has been pointed out previously† that the chance of these results for the lithium compounds (including Li3PO4. H,O) agreeing accidentally was about 1 in 280. (a) Richards and Meldrum (1917) give the melting-point of pure lithium chloride as 613° C. This makes for better agreement, giving N,X10-12=5×206. (b) The melting-point of lithium silicate is given as a standard temperature (1201 C.) in the Smithsonian Physical Tables. * H. S. Allen, Phil. Mag. vol. xxxiv. p. 478 (1917). (a) Melting-point of sodium chloride (801° C.) has been used as a standard temperature. (b) Melting-point of sodium nitrite, 271° C. (Divers, 1899), (a) Melting-point of the anhydrous salt, 96° C., Tilden (1884). (b) The melting-point of potassium sulphate (1070° C.) is used as a standard temperature. The results for sodium and potassium compounds are specially interesting, and should be compared with one another where that is possible. There are eleven cases in |