70 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



portions of the solution to confirm the result ; and as the depth of opales- 

 cence as seen in the nephelometer was perfectly fiat, without disturbing 

 eflections, the end point could be determined with great precision. 

 Several results obtained in this manner are given in Series II. 



SERIES II. 



These results, however, do not merit great confidence ; for the appara- 

 tus, which had become somewhat complicated, did not work smoothly 

 at first, on account of some minor imperfections which were remedied 

 later. Besides this, careful consideration led to the suspicion that the 

 towers used for drying the air and nitrogen were not efficient enough to 

 remove the last traces of water. Of necessity the towers had to be 

 charged with sulphuric acid an hour or two before their final use, and 

 during that time a large part of the acid drained out of the pumice stone. 

 This surmise was fully confirmed by later experiments ; and since this 

 was the case, the second series must be rejected in the final estimate of 

 the atomic weight. 



Third Series of Determinations. 



In order to remedy the most serious defect of the second series, the 

 arrangement for drying the air and nitrogen was much enlarged and im- 

 proved. By pouring sulphuric acid into the safety funnels at the top of 

 the many towers, from time to time, during the passage of the gas, the 

 glass beads were kept thoroughly saturated during the whole process. 

 Tlie sulphuric acid having reached the bottom of the column drained out 

 of the tubes provided for that purpose into beakers below. It will be 

 seen that by this means the efficiency of the apparatus was far greater 

 than in the previous form. As a test, a very rapid stream of wet air 



