X INTRODUCTION. 



suits was not discovered until recently. A large number of 

 computations had been actually finished, involving, among 

 other things, the greater part of Stas' work, when Dumas 

 published his investigation upon the occlusion of oxygen by 

 silver. Here it was shown that a very great number of 

 atomic weight determinations must have been vitiated by 

 constant errors, which, though constant for each series, were 

 probably of different magnitude in different series, and, 

 therefore, could not be systematically corrected for. At the 

 time of the announcement of this discovery of Dumas my 

 work was so far under way that I thought it best to com- 

 plete my discussion without reference to it, and then to 

 study its influence in the appendix. In the chapter upon 

 aluminum, however, it will be noted that Mallet eliminated 

 this error in great part from his experimental results. 



Necessarily, this work omits many details relative to ex- 

 perimental methods, and particulars as to the arrangements 

 of special forms of apparatus. For such details original 

 memoirs must be consulted. Their inclusion here would 

 have rendered the work unwarrantably bulky. There is 

 such a thing as over-exhaustiveness of treatment, which is 

 equally objectionable with under-thoroughness. 



Of course, none of the I'esults reached in this revision 

 can be considered as final. Every one of them is liable to 

 repeated corrections. To my mind the real value of the 

 work,' great or little, lies in another direction. The data 

 have been brought together and reduced to common stand- 

 ards, and for each series of figures the probable error has 

 been determined. Thus far, however much my methods 

 of combination may be criticized, I feel that my labors will 

 have been useful. The ground is now cleared, in a measure, 

 for future experimenters ; it is possible to see more distinctly 

 what remains to be done ; some clues are furnished as to the 

 relative merits of different series of results. I hope to be 

 able, from time to tinfe, as new determinations are published, 

 to continue the task here begun, and perhaps, also, to add, 

 in the near future, some data of my own establishing. 



In addition to the usual periodicals the following works 



