278 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Cerico-Molyhdates. 



When eerie fluoride, CeF4, is boiled in a platinum dish with 14 : 6 

 molybdate of ammonium, the solution quickly becomes yellow, and 

 soon deposits a fine yellow crystalline salt, which may be washed with 

 cold water, in which it is but slightly soluble. It contains molybdic 

 teroxide, eerie oxide, and ammonia. Basic eerie nitrate treated with 

 a solution of hydro-potassic fluoride, KFoH, changes character at once 

 and becomes flocky-crystalline. After washing with cold water, boil- 

 ing with 14:6 molybdate of ammonium dissolves but little, but the 

 salt becomes bright sulphur-yellow and crystalline and is practically 

 insoluble in water. The best method of preparing this salt consists in 

 first preparing pure basic nitrate of cerium* free from lanthanum 

 and didymium (neo-dymium and praseo-dymium). This is to be dis- 

 solved in nitric acid and the solution diluted. Acid potassic fluoride 

 then precipitates a nearly white flocky salt, which dissolves readily in 

 a boiling solution of 14 : 6 molybdate of ammonium to a yellow solu- 

 tion, and crystallizes from this. It will probably be better to boil with 

 a solution of an acid sodic molybdate, as this yields a soluble sodic salt, 

 the solution of which gives with ammonic chloride a yellow crystalline 

 precipitate of an ammonium salt, which will make a good starting 

 point for further investigations. 



When the eerie fluorine salt, prepared as above with KFoH, is 

 boiled with 10:4 sodic tungstate, a fine bright yellow solution is 

 formed which gives a beautiful orange crystalline precipitate with 

 nitrate of croceo-cobalt. In preparing the fluorine compound it is 

 best to add a cold filtered solution of KFgH to the basic eerie nitrate 

 diffused in cold water, and not to heat at all. Ceric hydrate dissolves 

 with difficulty in solutions of acid tungstates and molybdates, more 

 easily when precipitated from cold solutions. 



Note on Certain Tungstates, and on a new 

 Phospho-Tungstate. 



In other instalments of my work I have endeavored to show f that 

 there exists a special class of metatungstates, of which the lowest term 

 has the general formula 4 WO3 . RO, and the highest the general 

 formula 24 WO, . 11 R^O. This view appeared to be supported both 

 by my own work and by that of Marignac, but has not found favor 



* See my paper in American Journal of Science, XXXVII. 352. 

 t Proceedings of tlie American Academy, XV. 15. 



