8 On Isomeric Transmutation^ and the Nature of 



bility, specific gravity, &c., was always occasioned by difference 

 at least in the proportion of ingredients, and in most cases by 

 difference also in their nature ; and this is still acknowledged as 

 true in regard to the majority of substances ; water, e.g. is the 

 only body containing oxygen and hydrogen, in the proportion 

 of eight parts by weight of the former to one of the latter ; com- 

 mon salt is the only substance, with thirty-five parts of chlorine 

 to twenty-three of sodium, and so with other compounds. But 

 within the last few years many bodies have been discovered 

 containing the same elements, in the same proportion, and yet 

 differing in every physical and chemical property. A striking 

 example of this may be found in a group of organic substances 

 particularly referred to by Liebig in his Familiar Letters : — 

 " A great class of bodies," says he, " known as the volatile 

 oils, oil of turpentine, essence of lemons, oil of balsam of co- 

 paiba, oil of rosemary, of juniper, and many others, differing 

 widely from each other in their odour, their medicinal effects, 

 their boiling points, their specific gravity, &;c. are exactly 

 identical in composition ; they contain carbon and hydrogen 

 in the same proportions ;"* viz. five atoms of carbon to four 

 of hydrogen. Bodies which possess this peculiarity are termed, 

 in relation to each other. Isomeric (from /cog, equal^ and [J^z^og, 

 part), which may be Englished equiproportional, and marks 

 their possession of an equal proportion of the same elements. 

 The unexpected discovery of this curious law, while it has 

 shewn chemists that the greatest dissimilarity in the proper- 

 ties possessed by bodies may accompany the most perfect coin- 

 cidence in proportional composition, has, at the same time, 

 directly led to the conclusion, that the elementary bodies may 

 form a group, or a series of groups, related to each other iso- 

 merically, or equiproportionally, as the volatile oils referred 

 to, are. Who first detected the applicability of the law of Iso- 

 merism to the possible solution of the problem of the true 

 nature of the chemical elements, I do not know ; nor do I 

 profess to offer any historical sketch of the progress of specu- 

 lation on this subject. I need only mention, that three of our 

 living chemists have published views on the possible Isomerism 



* Familiar Letters on Chemistry, by Justus Liebig, pp. 47; 48. 



