738 THE POPULAR SCIENCE MONTHLY. 



passive principles. These elements, again, were not definite sub- 

 stances, but merely classes of products obtained by distillation, 

 the active principles being those that passed over and the passive 

 principles those that remained behind in this process — a process 

 which at the time had become the typical process of chemistry, 

 and the chemists of this period are always represented in paint- 

 ings with a retort or alembic, as were the alchemists of an earlier 

 period with a furnace and crucible. This last enumeration of 

 elements is not so different from that of the alchemists as would 

 at first sight seem, for mercury was regarded as the most active 

 of the spirits, and sulphur as one of the oils. Moreover, the dis- 

 tinction between fixed and volatile oils, which dates from this 

 period, shows the generic character of the elements then accepted. 



In his " Oedipus Chymicus," first published about the middle 

 of the seventeenth century, Becher, the author of the theory of 

 phlogiston, comes back to the elements of Aristotle, and in this he 

 is followed by Stahl, who elaborated the same theory a generation 

 later. To give an idea of the confusion of thought on this sub- 

 ject, even at a comparatively late period, I will quote from the 

 " Cours de Chimie, par M. L^mery, nouvelle Edition, Paris, 175G," 

 a work which remained one of the chief authorities on chem- 

 istry down to the time of Lavoisier. I translate freely from the 

 French : 



" The first element of compound bodies which we must accept 

 is a universal spirit, which, being universally diffused, produces 

 different results according as it is held in different matrices or 

 pores of the earth ; but as this principle is somewhat metaphysical 

 and can not be perceived by the senses, we must distinguish in 

 addition certain elements which are perceptible. I shall name 

 those commonly accepted. 



" As chemists in analyzing different compounds have found 

 five kinds of substances, they have concluded that there are five 

 principles of material things — water, spirit, oil, salt, and earth. 

 Of these five there are three which are active principles — spirit, 

 oil, and salt ; and two passive — water and earth. The first are 

 called active, because, being endowed with rajDid motion, they 

 determine the active qualities of the products into which they 

 enter ; and the second are called passive, because, being at rest, 

 they only serve to diminish the vivacity of the active principles." 



Then follows a more precise definition of the several principles 

 enumerated, to which in part I have already referred. After this, 

 L^mery remarks : 



" The term principle of chemistry must not be taken in an 

 exact sense, for the substances to which we have given this name 

 are principles only relating to our knowledge, and so far as we 

 have been unable to go further in the division of bodies. But we 



