Mr. M. M. Pattison Muir on Chemical Classification. 261 



weights of tliese bodies, and also that the chemical properties 

 vary in the same manner. 



32. If the specitic volnmes of the elements in the solid 

 state (that is, the volumes occupied by masses proportional to 

 the atomic weights of the elements) be arranged in order, 

 beo^innino- with that element >Yhich has the smallest atomic 

 weight, and if these numbers be compared with the atomic 

 weights of the elements so arranged, it will be seen that the 

 former numbers increase and decrease periodically with the 

 latter. Lothar Meyer has represented this fact graphically in 

 the form of a curve. In the table annexed to the Modernen 

 Theorien the atomic weights of those elements Avhich exist at 

 ordinary temperatures, or which can be obtained, in the solid 

 state, are laid off in a horizontal line ; vertical lines, repre- 

 senting the specific or atomic volumes of these elements, are 

 also laid off; and a curve is drawn through the extremities of 

 the latter lines. By noting some of the leading physical 

 properties of the elements on this curve, Meyer shows to the 

 eye the periodic nature of the connexion between the atomic 

 weights of these elements and those properties. For instance, 

 the atomic volume decreases from lithium through beryllium, 

 and reaches a minimum in boron, from which it again in- 

 creases through carbon, oxygen, and fluorine *, to sodium ; 

 the curve then passes downwards through magnesium to 

 aluminium, where it again turns, and after passing through 

 silicon, phosphorus, sulphur, and chlorine, reaches a second 

 maximum in potassium, and so on. Lithium, sodium, potas- 

 sium, rubidium, and probably caesium, mark maxima in the 

 curve of atomic volume. Boron, aluminium, cobalt, and 

 nickel, rhodium, &c., mark minima in this curve. 



The curve of atomic volumes shows also that elements with 

 equal or nearly equal atomic volumes are possessed of very 

 different properties, according as the element having the next 

 greater atomic weight has a greater or a smaller atomic vo- 

 lume than that of ^'^ element in question. In other words, 

 that if tAvo elements have equal atomic volumes, but if one be 

 situated on an ascending portion of the curve, its properties 

 are very different from those of the other situated on a de- 

 scending portion of the curve. 



The more ductile metals are situated at the maximum and 

 minimum points of the curve, or immediately foUoAV the 

 elements Avhich are situated at these points. The more brittle 



* For the metliod by wliicli Meyer has made probable determinations 

 of the atomic vokmies of these elements, as also of hydrogen in the solid 

 state, see Ann. Chem, Pharm. Snppl. Bd. v. p. 129 etseq. 



