Januaet 15, 1904.] 



SCIENCE. 



97 



served in 1880 by Schiitzenberger, who, by 

 the use of different atomic weights, ob- 

 tained analyses summing 101 instead of 

 100, expressed the opinion that the chem- 

 ical value of a constant weight, or rather 

 mass of an element, may vary; that the 

 so-called atomic weight of an element ihay 

 be simply the carrier of a certain amount 

 of chemical energy which is variable 

 within narrow limits. (See also Crookes.) 

 Wurtz's summary of Boutlerow's views, at 

 a meeting of the Chemical Society of Paris, 

 provoked an interesting discussion. Cocke 

 later published a statement that he had ex- 

 pressed similar views more than twenty- 

 five years before. That is, in 1855, he had 

 questioned the absolute character of the 

 law of definite proportions and had sug- 

 gested that the variability was occasioned 

 by the very weak affinity between elements 

 manifesting a fluctuating composition. 

 AYithout doubt 'The Possible Significance 

 of Changing Atomic Volume,'* in which a 

 suggestion as to the probable source of the 

 heat of chemical combination is put for- 

 ward by T. W. Richards, bears directly 

 vipon this phase of the problem. 



While the atomic mass values depend di- 

 rectly upon the ratio between the constit- 

 uents of the compounds, they rest equally 

 upon the molecular weights. Many of the 

 latter attributed to salts of some of the 

 rare earths depend solely upon the spe- 

 cifief heat determinations of Hillebrand 

 and Norton,^ Nilson and Pettersson,§ who, 

 in the light of subsequent investigations, 

 we know, worked with complexes. To be 

 sure, those elements which were apparently 

 exceptions to the law of Dulong and Petit, 

 possess low atomic weights (beryllium, 

 boron, carbon, silicon, aluminum and sul- 



* Proc. Am. A(^ad. Arts and Sciences, 27, 1, 1901, 

 and 27, 399, 1902. 



f Beiiclite, 13, 1401, 1880. 



tPofifi. Annal., 150 and following. 



^Berichte, 13, 146, 1880. 



phur') irand have for the most part been 

 brought into harmony. "The specific 

 heats of all substances vary with the tem- 

 perature at which they are measured; and 

 though the variation is often slight, it is 

 occasionally of relatively great dimensions. 

 When this is so in the ease of an element, 

 the question arises: At what temperature 

 must the measurement of the specific heat 

 be made in order to get numbers compar- 

 able with those of the other elements? No; 

 definite answer has been given to this ques- 

 tion, but it is found that as the tempera- 

 ture rises, the specific heat seems to ap- 

 proach a limiting value, and this value is 

 not in general far removed from that 

 which would make the atomic heat approx- 

 imately equal 6.4. ' '* In view of this, allo- 

 tropism, and the work of Richards ad- 

 verted to, it appears that a revision of the 

 specific heat values now taken is necessary 

 before we can accept fully this law, which 

 has been most helpful. 



Time will not admit of detailed state- 

 ments, and it is unnecessary in this presence 

 to more than call attention to the fact that 

 what has been said is not applicable to each 

 specific case. 'La critique est facile, mais 

 I'art est difficile,' as Berthelotf has said, 

 yet we must appreciate that all our laws 

 have their limitations. "Man being ser- 

 vant and interpreter of nature, can do and 

 understand so much and so much only, as 

 he has observed in fact or in thought in the 

 course of nature. Beyond this he neither 

 knows anything nor can do anything. "J 



A glance at the extensive, even censored, 

 list of claimants will evoke serious thought. 

 "Thus was the building left ridiculous. "§ 

 The difiiculties briefly outlined and the 

 causes for lack in uniformity are by no 

 means insurmountable, but will continue 



* ' Introduction to Physical Chemistry,' James 

 Walker, London, p. 33. 

 f ' Les Origines de I'Alchimie,' Paris, 1885. 

 J Bacon's ' Novum Organum,' Aphorism I. 

 § Milton, ' Tower of Babel.' 



