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TEE POPULAR SCIENCE MONTHLY 



3. Several compounds of this series, 

 which theoretically may exist, are un- 

 known. Thus, between arachidic and 

 behenic acids there is no acid corre- 

 sponding to Ch). Between behenic 

 and lignoceric there is none corre- 

 sponding to C22. Similarly, several 

 acids are missing between cerotic and 

 melissic. 



4. The vacant places are all found 

 in the lower part of the series, i. e., 

 among the heaviest molecules. 



5. Isomeric forms occur in the se- 

 ries, e. g., butyric and isobutyric, ca- 

 proic and isobutyl acetic acids. 



6. In a homologous series in gen- 

 eral, the melting points, boiling 

 points and specific gravities change 

 uniformly and progressively with in- 

 crease in molecular weight. In this 

 particular series (considering, as be- 

 fore, only the acids with normal struc- 

 ture) the boiling points and specific 

 gravities show this progressive change, 

 and the melting points do also from 

 caprylic acid on. 1 



7. The acidity decreases with in- 

 creasing molecular weight. 



3. Many elements which theory pre- 

 dicts should exist are unknown in the 

 Periodic Table. Thus, elements are 

 missing between silver and gold, be- 

 tween cadmium and mercury, etc. 



4. The vacant places all occur in 

 the lower part of the Periodic Table, 

 i. e., among the heaviest atoms. The 

 first four periods are complete (ex- 

 cepting the manganese family). In 

 the last three periods many empty 

 places appear. 



5. Allotropie forms occur in several 

 of the families, e. g., the various 

 forms of phosphorus, of sulphur, of 

 carbon. 



6. Generally speaking, the melting 

 points, boiling points and specific 

 gravities change progressively and 

 uniformly in each family of the ele- 

 ments with increase in atomic weight. 



7. The oxides of the elements be- 

 come successively less acidic (or more 

 basic) in each family with increasing 

 atomic weight. 



The above relations show that a family of the elements possesses all 

 the characteristics of a homologous series. There is evidently some 

 identity of principle in the two things compared. We know that in 

 the one case there is in the whole series a common plan of molecular 

 structure, the differences in the structures of the successive normal acids 

 being due to the constant and progressive addition of the same group 

 of atoms, CH 2 ; and hence it seems reasonable to suppose that there is 

 likewise in each family a common plan of atomic structure, 2 to which 

 are due the properties common to a family. 



1 The physical constants here used (as well as the tabulation of the acids) 

 are those given by Leathes, ''The Fats," pp. 10-11. Other authors include 

 several acids (e. g., pelargonic, undecylic) not mentioned by Leathes. 



3 For example, grouping of electrons, according to the well-known theory of 

 J. J. Thomson. 



