EXPERIMENTS ON CEtUTB. 109 



Cerium, like feveral other metals, appears fufceptible of two Cerium has two 

 very diftmft degrees of oxigenation: the oxide which contains GXldes * 

 lead oxigen is white; that which is Saturated with it is of a / 

 fallow red. Though they differ confiderably in certain refpecls, 

 their quantities of oxigen are not very difiimilar, whence they 

 are readily and eafily commutable into each other. 



The white oxide expofed to the blowpipe foon becomes red,Expofed to the 

 but does not melt, or even agglutinate. With a large propor- j^^pe w ^h 

 tion of borax it melts into a tranfparent yellow globule * : with 

 lefs the globule becomes opake on cooling. On heating gently 

 a tranfparent compound of borax and oxide of cerium it becomes 

 milky like a tin enamel. i 



The white oxide of cerium becomes yellowifh in the open Takes oxigen 

 air, but never fo red as by calcination, becaufe it readily com- *"id fronTthe 

 bines wrth carbonic acid, which oppofes its union with oxigen air. 

 to the point of faturation, and becaufe it always retains a por- 

 tion of water, which diminithes its colour. 



Cauftic potalh by the alliiUnce of heat deprives the red oxide Alcalies do not 

 of part of its oxigen, and renders it white. This being dried, 3 on l ' 

 however, and urged to the ftate of fufion, becomes red again. 

 Alcalies have no other a&ion on it. £ 



Sulphuric acid diflolves the red oxide with great difficulty. Sulphuric acid 

 Equal parts of it and of lulphuric acid diluted with four times * lth the red ox " 

 its weight of water combine readily when heated : the whole 

 mafs ailuming a cryftalline form and brilliant afpect. On adding 

 frefti acid, and heating them together a long time, a complete 

 folution takes place. This folution being evaporated by a gentle 

 heat cryitallizes in very fmall needles, fome of which are Two fulphates, 

 orange +, others of a lemon colour. If evaporated quickly, 

 nothing but a yellow powder is obtained. 



50. The increafe of weight they afcribe to oxigen abforbed by the 

 iron and the cerium. ' ^ 



* Firft blood-red, then, as the heat decreafes, green, yellowilh, 

 and finally coiourlefs. If it be kept in the middle of the flame it 

 continues as clear and coiourlefs as glafs. Thefe phenomena are With a phof- 

 more evident, if a phoiphoric fait be employed. If two coiourlefs phoric fait, 

 tranfparent globules, one formed with borax the other with a phof- 

 phoric fait, be fufed together, a tranfparent compound is produced, 

 which on cooling becomes opake, and of a pearl colour. Meflls. 

 H. and B. 



f Thefe Meffrs. H. and B. confider as an acidulous fulphate of 

 cerium at a maximum of oxidation. 



The 



