150 Mr. H. Robinson. A ReJetermination of [June 1'.', 



depend on any peculiarity in tho animal, but simply on tbe reaction 

 of its urine at the time. 



Tho original view of the author, which led to his making the 

 numerous observations above mentioned, which also be enunciated in 

 his communication of February, 1883, appears to be fully verified by 

 them ; and the conclusion may fairly be drawn that, under ordinary 

 circumstances, the absence of uric acid from the urine of the adult 

 horse is not due to the non-formation of this acid, but to the destruc- 

 tion which it undergoes when formed, so that, if at any time the 

 destructive influence is removed by the fluid assuming an acid reac- 

 tion, uric acid appears in the urine. 



Lastly, we may derive from the above observations an explanation 

 of the fact that uric acid is present in the urine of the suckling 

 herbivorous mammal, for in such animals the urine is found to be 

 acid in reaction. 



XIII. " A Redetermination of the Atomic Weight of Cerium." 

 By HENRY ROBINSON, B.A., Assistant to the Professor of 

 Chemistry in the University of Cambridge. Communicated 

 by Professor LIVEINU, F.R.S. Received June 11, 1884. 



Having worked a good deal during the last few years on the pre- 

 paration of pure compounds of the cerium and yttrium metals, I was 

 led to seek some method by which I might obtain their anhydrous 

 chlorides in such a state of purity that it would be possible to make 

 from them redeterminations of the atomic weights of the metals. In 

 April last year, I succeeded in preparing anhydrous cerium chloride 

 (and in this paper I shall confine myself to that metal) by passing 

 dry hydrochloric acid gas over what I may call air-dry cerium 

 oxalate, heating it at first gently, so as not to char the oxalate, and 

 then, as the operation proceeded, increasing the temperature to 

 a full red heat. The chloride so obtained was perfectly white, 

 and, when thrown into water, dissolved, with a hissing noise and a 

 considerable evolution of heat, to a clear and colourless solution. I 

 obtained the chloride so easily on the first attempt, I supposed I could 

 repeat the experiment at will, but such did not prove to be the case, 

 and, being much occupied with other duties, not much more was 

 done towards the attainment of my object until the commencement of 

 the present year. I had previously prepared a considerable quantity 

 of pure cerium oxalate, in the following manner, from a crude yellow 

 sulphate obtained from Schuchardt. It contained much didymiumand 



