153 



of carbon, which all appear to have the same structure as 

 iphitc itsrll. He found that the carbon-atoms are placed hen- in tin- 

 n UTS of regular hexagons arranged in parallel strata, the fourth 

 Irmy of the carbon-atom being reduced to an extremely weak 

 1 1 1 is fact seems to prove that the carbon-atom can act as a centre 

 of jour, or of three equal valencies, and the phenomena ob- 

 give to some extent an explanation of the possible occurrence 

 drd vatives of /n'valent carbon (as triphenylmethyl, etc.) and of 

 specific nature of the "aromatic" nucleus with its "paralysed" 

 inu-ies. 



27. Without going into further details of these highly important 

 ivestigations, or into the discussions and problems which they entail, 

 may bring to the fore the following salient points from the above : 

 i). Direct experimental proof is given of the correctness of the view 

 it the component particles in crystals are arranged in space-lattices, 

 i was already foreshadowed by crystallographers some sixty years ago. 

 b). Direct proof is given of the correctness of the other view 

 John eke, Groth 1 ) that the unlimited regular structures we call 

 jstalline substances, may be considered as being built up by the 

 ilar interpenetration of such space-lattices, each of which con- 

 of one and the same kind of atoms. These atoms plainly preserve 

 jrefore their individuality as constituents of such crystalline 

 ibstances. 



Because of the periodical character of these unlimited regular 

 stems, it is from a mathematical and crystallographical point 

 view absolutely arbitrary, in which way we wish to imagine these 

 )ms to be combined into larger units, although we have at present 

 idea, in what way and by what forces the "chemical molecule" 

 preserved in such a structure 2 ). 



The notion of "crystal-molecule" as a structural unit has therefore 

 st its significance from a crystallographical standpoint: the whole 

 stal, endlessly extended in all directions, is one single gigantic 



1) P. Groth, Ber. d. d. Chem. Ges. 47. 2063. (1914); Zeits. f. Kryst. 54. (1915). 

 According to this author the interatomic connections must remain, even if from 

 a crystallographical point of view the chemical molecule as such has lost its 

 significance. Many crystals have symmetry-elements, the special nature of which 

 is obviously closely related to the atomic structure of the chemical molecule itself. 

 This can only have any significance, if the latter remains present in the crystal. 



) Most recently J. Beckenkamp (Centralbl. f. Miner. (1917), p. 97110 

 has made some suggestive suppositions about the preservation of "chemical mole- 

 cules" in crystalline media 



