360 PROCEEDINGS OF THE AMERICAN ACADEMY 



obtained by me. I have hitherto abstained from making any remarks 

 upon these researches, or from entering upon any defence of my own 

 work, from the conviction that a determination of an atomic weight, if 

 correct, would certainly be in the end received, and if incorrect, would 

 as certainly be superseded by a better. 



The equivalent found by Berzelius * was 129, when reduced to the 

 scale on which H = 1, and it is remarkable as being the only instance 

 in which a grave error has been detected in the numerous determina- 

 tions to which he devoted a large part of his life. 



Passing over the equivalent of Berzelius, which is now admitted to 

 be altogether too high, the other determinations may be divided into 

 two classes ; those of Schneider and H. Rose, which place the equiva- 

 lent at about 120, and those of Kessler, Dumas, and myself, which 

 give a number not varying much from 122. Kessler claims to have 

 been the first to show the error in the equivalent which had been uni- 

 versally adopted on the authority of Berzelius. His earlier experi- 

 ments gave 123.58 to 123.84 for the atomic weight.f 



A few months later appeared the elaborate research of R. Schneider 

 of Berlin.J A native sulphide of antimony, said by him to be free from 

 appreciable quantities of arsenic and the metals by which it is usually 

 accompanied, served as the basis of this work. The sulphide was 

 reduced, at a temperature just sufficient to fuse it, by a slow stream of 

 pure hydrogen. The loss of weight, after applying small corrections 

 for a minute quantity of quartz present, for a portion of the antimony 

 volatilized, and for a trace of sulphur retained by the reduced metal, 

 gave the necessary data for the calculation of the atomic weight. 



It is an invidious task, especially for a fellow-laborer, to examine 

 into the causes of error in a work so elaborately and conscientiously 

 executed. The results show, however, and Schneider himself ad- 

 mits the presence of, some constant error, in consequence of which the 

 proportion of antimony in the sulphide seemed to increase regularly 

 with the quantity of material operated upon. So that those determina- 

 tions gave the highest atomic weight in which the largest quantity of 

 sulphide was employed. I am inclined to think that the error may 

 have arisen in part from the action of the flame upon the glass of the 



* Schweigg. Journ., Bd. VI. S. 144, and Bd. XXII. S. 69. 

 t Fogg. Ann., Bd. XCV. S. 204. 

 t Ibid., Bd. XCVIII. S. 293. 



