152 Mr. H. Robinson. A Redetermination of [Juno !'., 



centiras. of strong acid in 1000 cub. centims. of water by which 

 the cerium nitrate was decomposed into a basic nitrate which gene- 

 rally settled down readily, leaving only a small quantity of cerium in 

 solution. The clear liquid was siphoned off and saved for further 

 treatment. The basic nitrate was thrown on a filter, drained at the 

 pump, and slightly washed with dilute nitric acid. It was removed 

 from the filter-paper, transferred to an evaporating basin, and 

 thoroughly heated on a water-bath until quite dry and hard, then 

 broken up with a pestle in the dish, again set on the water- bath and 

 heated, and, while there, drenched with boiling dilute nitric acid of 

 the same strength as that used before. It was kept hot on the water- 

 bath for some time and constantly stirred, then, after standing a 

 short time, the greater part of the nearly clear supernatant liquor was 

 poured away and the precipitate transferred to a filter, where it was 

 drained by means of the pump and thoroughly washed with dilute nitric 

 acid until some of the basic nitrate taken from the filter and dissolved 

 in hydrochloric acid, so as to make a very concentrated solution, showed 

 no trace of the didymium absorption- bands. When this point was 

 reached the basic cerium nitrate containing a little lead was removed 

 from the filter and put in a flask, hydrochloric acid was added, and 

 the whole heated on a water- bath until the nitrate was converted into 

 chloride and dissolved. The greater part of the excess of hydro- 

 chloric acid was evaporated away, as the oxalate of cerium, to be 

 obtained subsequently, was found to be rather soluble when much of 

 that acid was present. The cerium chloride was dissolved in water 

 and the solution saturated with sulphuretted hydrogen, then filtered 

 from the lead sulphide ; the filtrate was boiled to get rid of the sul- 

 phuretted hydrogen, and again filtered to remove the small quantity 

 of sulphur which separated out. The warm solution was then satu- 

 rated with chlorine, and left to stand all night, so that if any iron 

 was present it might be peroxidised. The cerium was then precipi- 

 tated from the acid solution by well purified oxalic acid ; the oxalate 

 was allowed to settle down thoroughly, and the clear liquor was 

 poured away. After several washings by decantation, using a dilute 

 solution of hydrochloric acid containing about 2 per cent, of hydro- 

 chloric acid, the oxalate was transferred to a funnel which held a 

 perforated platinum plate in its neck, and well washed with boiling 

 water, then dried on the water-bath. All the cerium oxalate I have 

 used in my experiments was prepared in the way just described. 

 When I had obtained a sufficient quantity, the whole was well mixed 

 in a mortar and then placed in a rather loosely stoppered bottle. 

 From time to time a quantity sufficient for each experiment was 

 taken from this bottle. When I had prepared all the pure oxalate I 

 required, I hit accidentally on a simpler mode of separating cerium 

 from lanthanum and didymium. Instead of precipitating the cerium 



