1 38 Mr. W. N. Shaw on the Atomic 



the dissociation of acetic acid from (C 2 H 4 2 )» into w(C 2 H 4 2 ) 

 no longer conjectural. 



If it be granted that our thesis is proved, that the molecules 

 of stable liquids are not more complex than those of their 

 gases, it follows that the difference between liquids and gases 

 is one of degree, not of kind ; is quantitative, and not quali- 

 tative. 



University College, Bristol, 

 November 18, 1886. 



Eerata in article in January number : — Page 62, lines 5 and 4 from bot- 

 tom, for p=a-\-boc t +cfi t read log p = a-\-b» t -\-c/i t ; for p^a+boc* read 

 log p = a+bat. Same correction on p. 64, fifth line below table ; and 

 p. 68, line 1. P. 64, line 3 below table, for 25-54 millim. read 26*54 

 millim. P. 68, line I, for log =0-5784772 read log 6=0-5784772. 



XVI. On the Atomic Weights of Silver and Copper. 

 By W. N. Shaw,' ' M.A* 



IN the table of atomic weights given by Landolt and Born- 

 stein in their Physikalisch-Chemische Tabellen, p. 1, that 

 of copper is quoted as 63*18 from L. Meyer and K. Seubert, 

 and as 63*17 from Clarke. These numbers give the chemical 

 equivalent of dyad copper as 31*59 and 31*585, respectively. 

 If we take the value of the atomic weight of silver as 107*66, 

 we get for the ratio of the chemical equivalents of silver and 

 copper 3*4080 or 3*4086. 



The atomic weight of silver is given as one of those whose 

 accuracy is of the first order, with a possible error less than 

 *05 ; that of copper is, on the other hand, placed in Class III., 

 for which the possible error may reach 0*5. The possible 

 limits assigned by this to the ratio of the chemical equivalents 

 are 3*381 and 3*435. The principal determinations of the 

 atomic weight of copper are bv Berzelius, Erdmann and Mar- 

 chand and Hampe ; and the methods used may be called strictly 

 chemical. Hampe used an electric current to extract all the 

 copper from a solution of the metal, and further tried to de- 

 termine the ratio of the equivalents by comparing the electro- 

 lytic deposits of silver and copper in the same circuit ; but he 

 abandoned the method as unsatisfactory. I have communi- 

 cated to the Electrolysis Committee of the British Association 

 the details of a number of experiments carried out at the 

 Cavendish Laboratory under my direction, designed to deter- 

 mine the amount of copper deposited in cells with different 

 current-densities from a nearly saturated solution of copper 



* Communicated by the Author. 



