152 POPULAR SCIENCE MONTHLY. 



THE PEEIODIC LAW. 



By Professor JAS. LEWIS HOWE, 



WASHINGTON AND LEE UNIVERSITY. 



BEFOEE the time of Lavoisier ideas concerning the nature of mat- 

 ter were mere speculations. Following the introduction, at the 

 close of the eighteenth century, of the conception of the indestructi- 

 bility of matter, and more especially with the introduction of the atomic 

 theory a decade or so later, the idea of some sixty or seventy absolutely 

 different kinds of matter received general acceptance. The unity of 

 these different elements was, indeed, held by some, but as a pure specu- 

 lation, while the evidence was all against it. It remained for the 

 Periodic Law to show that there is a connection between these different 

 elements. It is true, we are as far as ever from any knowledge of what 

 that connection is, or from any knowledge of the nature of that primal 

 substance out of which all matter is shaped, unless, indeed, the recent 

 work of J. J. Thomson and others on the electric condition of gases 

 is pointing us thitherward. 



The early attempts to classify substances from a chemical, or rather 

 alchemistical standpoint, were wholly superficial. Pliny, for example, 

 describes two forms of lead, plumbum nigrum and plumbum candidum. 

 The former term was used for lead proper, the latter for tin, though 

 these two metals have little resemblance, except in their low melting 

 points. Sulfuric acid was classed with the oils, as oil of vitriol, and 

 the name has popularly and technically remained to the present, al- 

 though the only resemblance of sulfuric acid to an oil is in its appear- 

 ance. The chlorids of antimony and of tin were known respectively as 

 butter of antimony and butter of tin, from the fact that they are semi- 

 solid substances, of much the same consistency as butter from milk. 

 Even to-day we speak familiarly of milk of lime and milk of sulfur, 

 though but for the fact that they are whitish liquids, they have nothing 

 in common with the product from the cow. Perhaps to us one of the 

 most remarkable instances of classification was the association of the 

 black oxid of manganese with the white oxid of magnesium, commonly 

 known as calcined magnesia. The only property common to these two, 

 magnesia nigra and magnesia alba, as they were early called, is that 

 both are fine powders. In the seventeenth and eighteenth centuries the 

 discovery of the different gases began, and to the workers of that day 

 all were but different kinds of air. Thus we find 'inflammable air* as 

 the name for hydrogen, 'fixed air* for carbonic acid gas, and 'dephlo- 

 gisticated marine acid air" for chlorin. That no better principle of 



