322 Dr. T. Oarnelley on the 



somewhat uncertain. — As a case in point, wo liavo uranium, to 

 which the atomic weight 120 was formerly assigned. Men- 

 deljeff, however, pointed out in his original memoir that the 

 true atomic weight of this element ought to be 240 ; and this 

 number is now generally adopted. 



(5) To the Completion of our Knowledge of the Combination 

 forms of Chemical Compounds. 



Meyer's Curve of the Elements. — In December 1869, shortly 

 after MendeljefF proposed his periodic law, Lothar Meyer 

 published a very interesting article in Liebig's Annalen " On 

 the Nature of the Chemical Elements as a Function of their 

 Atomic Weights," in which he showed that by taking the 

 atomic weights as abscissae and the corresponding atomic 

 volumes as ordinates, a curve is obtained which is a visible re- 

 presentation of the fact that not only the atomic volume, but 

 also all the properties of the elements are a periodic function 

 of their atomic weights. As the atomic weight increases, the 

 atomic volume increases and decreases regularly in such a way 

 that the curve which represents these periodic changes is 

 divided by 5 maxima into 6 divisions, each of which has the 

 form of a suspended chain. Of these divisions, the 2nd and 

 3rd, and likewise the 4th and 5th, are very similar to one 

 another, and are of nearly equal dimensions. The 6th divi- 

 sion is at present incomplete. The 2nd and 3rd divisions cor- 

 respond to MendeljefFs short periods, viz. Li to F and Na to 

 CI, and the 4th and 5th divisions to two of his long periods, 

 viz. K to Br, and Kb to I. 



As a general rule, those elements standing in correspond- 

 ing parts of the curve have similar properties. In divisions 

 2 and 3 the atomicity increases regularly as we pass from left 

 to right down the curve till we come to the lowest point, 

 where the atomicity attains a maximum; and then, on rising up 

 on the opposite side of the curve, the atomicity gradually de- 

 creases again till it becomes unity. In the other divisions of 

 the curve the atomicity increases as we pass down the curve 

 from left to right, but in this case comes to a maximum half- 

 way down the curve, after which it decreases again, and attains 

 a minimum at about the lowest point ; and then as the curve 

 rises again, the atomicity undergoes exactly the same changes 

 as it did on the falling portions of the curve. Metals which 

 are easily expanded by heat lie at or near the maxima, whilst 

 those with a small coefficient of expansion stand at or near the 

 minima. Heavy brittle metals occur just before the minima 

 on the falling portions of the curve. All those elements which 

 occur on the rising portions of the curve are brittle non- 

 metallic elements. 



