606 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



These last three determinations were very kindly made by Dr. H. G. 

 Parker immediately after the completion of the magnesium work, and all 

 the precautions discussed in that description were heeded. It is a pleasure 

 to express my indebtedness to Dr. Parker for this assistance. 



The analysis of the three fractions of crystallized salt were made by 

 comparison with silver, using solutions at least as dilute as decinormal, 

 and determining the end point by observing with the help of the nephe- 

 lometer when the supernatant mother liquor contained equal concentra- 

 tions of silver and chlorine. 



A preliminary experiment with salt of less purity need not be de- 

 tailed. The table below contains the essential data and results of the 

 four consecutive final determinations, the only ones which were made. 



The Ratio of Strontic Chloride to Silver. 



If silver is assumed to have an atomic weight of 107.93, and chlorine 

 35.455, according to usual custom, the atomic weight of strontium cal- 

 culated from these results becomes 87.697. This result, greater by 0.033 

 than the value found from the bromide, indicated the presence somewhere 

 of an unknown source of error; and the results were left unpublished for 

 ten years because of the doubt therefore attaching to them. 



This doubt has now been wholly dispelled by the discovery of an 

 error in the assumed atomic weight of chlorine. It now appears that if 

 silver is taken as 107.93, chlorine must be 35.473 ; * and the atomic 

 weight of strontium calculated upon this basis becomes 87.661, a value 

 essentially identical with that found from the bromide, 87.663. 



* Riciiards and Wells, in an investigation now being published by the Carnegie 

 Institution. The somewhat lower value, 35.467, which was first announced as tlie 

 outcome of this work, was the result of preliminary experiments only. 



