42 Coward & Harden, Dalton's Lecture Sheets. 



represent the composition of "compound atoms" of the 

 most diverse inorganic and organic compounds. 



Very little of Dalton's published work deals with 

 organic compounds. The sheets show, however, that he 

 used his atomic symbols for picturing the constitution of 

 the commoner compounds of vegetable and animal origin, 

 probably for exhibition during courses of lectures on 

 pharmaceutical chemistry. The symbols were not put 

 together in a haphazard fashion ; for example, Dalton 

 introduced a " vegetable atom," composed of one atom 

 each of carbon, hydrogen and oxygen, as a constituent of 

 such different substances as citric acid, sugar and wood. 

 This conception of the radical marks an intermediate 

 stage between Lavoisier's idea and the later theories of 

 compound radicals. Dalton also clearly expressed by 

 his symbols the conception of isomerism, as shown by 

 sheet 23 (reverse), reproduced in Plate VII. , where the 

 compound atoms of two different substances are repre- 

 sented by " ultimate atoms," the same in nature and 

 number but differently arranged. 



Surprise has been expressed that Dalton could not 

 bring himself to adopt Berzelius' system of chemical 

 nomenclature. These diagrams, especially those dealing 

 with organic chemistry, render Dalton's attitude towards 

 Berzelius' system much more intelligible; for his sym- 

 bolic expression of the constitution of substances is much 

 simpler than that of Berzelius. It may indeed be said 

 that while modern chemistry has adopted the symbols of 

 Berzelius, it has used them much in the Daltonian fashion. 



Dalton's formulae for organic compounds are, however, 

 very different from those now accepted. 



One of the two sheets of atomic weights seems to 

 have been the second ever presented to the public. It 

 was prepared, together with several of the other sheets, 



