ELISHA MITCHEIvIy SCIENTIFIC SOCIETY. 69 



pressed upon all who desire the advancement of the 

 science. 



HOW FAR IS ACCURATE KNOWLEDGE OF THE ATOMIC 

 WEIGHTS ATTAINABLE? 



The atomic weiofhts are generally considered the 

 most important constants in chemistr}^ and A^et so im- 

 perfectly are they known and so varying the numbers 

 assigned them that it has not been possible so far to 

 settle finally whether they realh^ are constants or vari- 

 ables w^ithin narrow limits. The probability, however, 

 is so greatly against this latter view that the;.-e are few 

 who are inclined to accept it. As more than three 

 quarters of a century of work has been expended upon 

 them, work engaging the utmost efforts of the masters 

 of the science, as Berzelius, Dumas, Marignac, Stas 

 and many others, it may with perfect justice be asked 

 whether absolute accuracy is attainable. 



Some have hoped that the more perfect knowledge 

 of the chemists of the present, the better methods of 

 separation, purification and general manipulation, and 

 the fine balances, would enable them to attain to the 

 desired accuracy. There have been, of course, many 

 improvements but any one who will carefully examine 

 the determinations of Berzelius will find many of them 

 in marvellous agreement with the finest work of late 

 times and when he goes over the list and sees for how 

 many of these atomic weights the work of Berzelius is 

 still relied upon as the best, he will be less boastful of 

 the progress and less hopeful of results from it. 



Certainh% if accuracy is to be attained, then the 

 usual method of those who re-calculate these weights, 

 and in fact the only allowable method at present, 



