740 THE POPULAR SCIENCE MONTHLY. 



tion in 1794. Fourcroy, more fortunate than his greater colleague, 

 passed through this fearful period unharmed, although he was a 

 member of the Constituent Assembly, and after the fall of Robes- 

 pierre acted as Secretary of Public Instruction. He was made 

 senator by Napoleon, and died full of honors in 1809, living until 

 the decomposition of the alkalies and alkaline earths had become 

 accomplished facts. As before, I translate from the French very 

 freely : 



" Since the revolution effected in chemistry between 1774 and 

 1784'' (the period of Lavoisier's active scientific work) "by the 

 new discoveries which have entirely changed the face of the sci- 

 ence, many of the former erroneous and arbitrary distinctions 

 have been given up. The term principle is no longer used except 

 in a very general sense, and with the understanding that it applies 

 to different sorts of bodies, some of them simple and some of them 

 compound, depending on the nature of the materials from which 

 they come and on the method of analysis used. All chemists 

 agree to-day that if by principles or elements we understand the 

 original and simple bodies which constitute the primitive mole- 

 cules of substances, such bodies are wholly unknown, either as 

 regards their number or their x^roperties, and that in discussing 

 them we are yielding to theories as useless as those of monads or 

 atoms. They further agree that if we confine the word elements 

 to the last products of analysis which can not be subdivided by 

 analytical means, we must exclude from this class of bodies both 

 the so-called principles of the elder chemists and the four elements 

 of Aristotle, as many of these are compound substances, and we 

 must accept a very much larger number of elements than former- 

 ly, for we are acquainted with more than thirty substances which 

 can not be decomposed. 



" From the results of numerous and exact analyses chemists 

 know, first, that all natural substances may be divided into simple 

 and compound substances ; secondly, that the true distinction of 

 primary or simple substances is ability to resist decomposition, so 

 that the word simple is synonymous with the word undecompos- 

 able ; thirdly, that by compounds we signify substances which are 

 susceptible of analysis, or from which we can extract materials 

 more simple, or of which the complexity of composition dimin- 

 ishes in degree as the analysis is extended ; fourthly, that although 

 compounds of the same class may differ greatly among themselves, 

 it is sufficient for comparison and gives us an exact distinction if 

 we divide them into binaries or compounds formed of two ele- 

 ments, ternaries or compounds formed of three elements, quater- 

 naries or compounds formed of four elements, quinaries, sextaries, 

 etc., according as the number of the constituent elements increases; 

 fifthly, that the number of the constituent principles or compo- 



