1">| Redetermination of the Atomic Weiyht of Cerium. [June 19, 



chloride is at once detected. The credit of originating it is due to 

 Stas. With a little practice it soon becomes eapy by observing the 

 amount of turbidity produced by each addition of the silver nitrate 

 to the chloride to know how many drops may be added the next time 

 with safety, and as one drop of the solution of silver nitrate I used 

 contained only ^ of a mgrm. of silver there was not much danger of 

 adding an appreciable excess. 



I have made seven determinations of the chlorine in cerons 

 chloride by the method I have just described. The mean of these 

 determinations gives 139*8584 as the atomic weight of cerium when 

 the atomic weight of hydrogen is taken as 1 ; if that of oxygen is 

 taken as 16 then the number for cerium becomes 140*2154. 



I have taken the specific gravity of cerous chloride by weighing it 

 in carefully purified benzene, and I find it to be 3*88 compai'ed with 

 water at 15*5. Then making corrections for weighing in air for 

 both the brass and platinum weights and for the cerous chloride, I 

 find the atomic weight in vacuo when hydrogen is 1 to be 139*9035, 

 and when oxygen is 16 to be 140*2593. I thus find the atomic weight 

 of cerium to be lower than Biihrig did, but I defer making comments 

 on the work of others who have preceded me until I have made 

 some determinations of cerous bromide. This latter compound 1 have 

 already succeeded in making by passing hydrobromic acid over cerium 

 oxalate. 



The ratios I have employed in this paper are those of Stas, and are 

 as follows : If the atomic weight of hydrogen is 1, that of oxygen 

 is 15*96, silver is 107*66, and chlorine 35*37. 



The atomic weight of oxygen being 16, that of silver is 107*93, 

 ahd of chlorine 34*457. 



The table below shows the quantities of silver and cerous chloride 

 used in each experiment, and the ratios obtained. 



