December 30, 191 5] 



NATURE 



477 



jrvice. They may be compared to the maps 



rhich aid in the initial stages of an exploration ; 



te all maps of a partially surveyed district, they 



lay be imperfect and at times even erroneous ; 



ley indicate not only trodden paths, but suggest 



jw routes ; they serve to confirm imperfectly 



fctablished facts, and lead to the correction of 



rors. It is almost a platitude to say that nearly 



;ry new departure in science seems at the time 



^is made to have no very obvious relation to the 



;ds or conditions of our daily life. No one can 



)ssibly set a limit to the prospective usefulness 



of even the most recondite physical fact. 



In the book before us, which has occupied 

 nearly eight years in its preparation, Mr. Le Bas 

 has brought together the results of the large 

 amount of experimental work which has been 

 spent upon the subject of the molecular volumes 

 of liquid compounds since the time of Kopp, now 

 upwards of seventy years ago. Kopp was not the 

 first to attack this subject, but he was certainly 

 the first to attempt to give a definite significance 

 to the conception by seeking to establish the con- 

 ditions under which proper quantitative values 

 might be ascertained. Up to his time no 

 rational method had been suggested whereby 

 these values could be determined under presum- 

 ably comparable conditions — say, at their normal 

 melting- or boiling-points. Objections, of course, 

 may be urged against the employment of either 

 the melting point or the boiling point as a valid 

 condition of comparison, but in Kopp's time no 

 other course was open to him, and there can be 

 no question that it did serve to bring out regu- 

 larities and relationships which otherwise would 

 have been wholly obscured. Kopp's example in 

 this respect has been followed by almost every 

 subsequent worker in this special field. It is with 

 the large mass of material which has thus been 

 accumulated that Mr. Le Bas's book mainly deals, 

 and it is for the reason that the work is funda- 

 mentally based upon the principles laid down by 

 Kopp that the particular form of its title is due. 



Of course, Kopp and his immediate followers 

 suffered under the disability that present-day con- 

 ceptions of chemical constitution were wholly un- 

 known to them, and possibly even wholly 

 undreamt of. These ideas are mainly due to a 

 development of the chemistry of carbon com- 

 pounds long subsequent to Kopp's day. Although 

 Kopp made determinations of unimpeachable 

 experimental accuracy on a number of organic 

 compounds, his interpretation of the results they 

 afforded was limited, and, indeed, occasionally 

 erroneous, owing to his lack of knowledge of the 

 effect of constitutive influences. He compared 

 things between which we now know no real 

 NO. 2409, VOL. 96] . 



analogy exists, and made generalised deductions 

 from / wholly irrelevant and inconsistent data. 

 The work of his successors was more or less 

 guided by the light of contemporary theory, but,, 

 of course, even in their case it only reflects the 

 state of knowledge or speculation at the parti- 

 cular period it was undertaken. 



Now the great merit of Mr. Le Bas's mono- 

 graph is that it not only collects and groups in a 

 systematic arrangement the results of all the work 

 hitherto published on the molecular volumes of 

 liquid chemical compounds, but it discusses and 

 seeks to interpret these results with the aid of 

 all that is known or surmised concerning the 

 constitution of such compounds, however it may 

 have been ascertained. In this manner Mr. Le 

 Bas has been able to give a great expansion and 

 at the same time a greater precision to the con- 

 ception of the intimate relation which indubitably 

 exists between such a physical property as mole- 

 cular volume and chemical constitution. Thus 

 he shows, for example, that no physical property 

 is apparently so well adapted to elucidate the ring 

 structure of a compound as its molecular volume, 

 and he expresses the hope that this will hencefor- 

 ward take its legitimate place among other physi- 

 cal properties as an instrument of research. That 

 the determination of this value is readily possible, 

 and with a degree of accuracy amply sufficient for 

 its purpose as an indicative factor, had already 

 been shown by the author. He finds that the 

 values at the boiling point may be calculated with 

 approximate accuracy by the following simple 

 formula : — 



'-ir-i^-m 



the only data necessary being the density at 0° 

 and the boiling point. The mean value of the 

 constant c, as deduced from a considerable num- 

 ber of inorganic liquids investigated by the present 

 writer, is o'463. An almost identical value of c 

 is obtained for organic cyclic compounds without 

 side-chains. By means of the above formula the 

 molecular volumes of liquid compounds may be 

 calculated with an error of less than i per cent. 

 In open-chain compounds the value of c increases 

 by 0*024 for every addition of CH2. 



The book concludes with a suggestive summary 

 of the theory of molecular volumes, in which the 

 author discusses the present position of the additive 

 principle, its value, and its limitations. He clearly 

 shows, what, as he observes, had already been 

 pointed out by the present writer, that there is a 

 periodic relation in the atomic values of the vari- 

 ous elements, and he illustrates this by a diagram, 

 with special reference to the non-metallic ele- 

 ments. He summarises the discussion in the 



