1889.] NATURAL SCIENCES OF PHILADELPHIA. 165 



separating either erbia or terbia, hence the results obtained can 

 only be considered approximate. 



The material enveloping the Gadolinite seems to be amorphous ; 

 dull, with an uneven fracture and brittle ; its color is grayish brown ; 

 streak red, when powdered bright red. 



It was found necessary the float off the suspended part in water 

 from another portion which was not decomposable by hydrochloric 

 acid, and this was repeated until a sample was wholly decompos- 

 able by that acid. The silica did not gelatinize. 



Hardness = 3. Sp. Gr. = 3-494. 



Not fusible before the blow-pipe. The fluxes indicated iron ; 

 heated in a tube it gave water. Heated with carb. soda upon char- 

 coal it afforded a dark brown slag. 



The analysis indicated great complexity of mixture : — 



f cent. O = 9-676 



The approximate O ratios of the sum of the monoxycls are equal 

 to the tetraoxyds, or about two, whilst the O ratio of the dioxyds 

 and the sesquioxyds are each nearly one, hence this general 

 expression is proposed. : — 



2 (RO+R 3 4 ) Si0 2 (R 2 3 ) 



The question whether this substance is a mixture or not, I en- 

 deavored to solve by this consideration : sesquioxydes of iron as 

 goethite, limouite, etc., are respectively soluble to some extent in a 

 strong solution of citric acid ; if any of these oxyds should be mixed 

 or occur as such in the mineral a test with that acid would indicate 

 the fact. The test was made ; for several hours the fine red mineral 

 powder was kept in contact with a strong solution of citric acid at 

 ordinary temperature, about 70° F. and agitated occasionally with 

 no effect. If heated on steam bath the effect was very slight. It 

 seems, therefore, that the substance is not a mixture, but a hyd rated 

 tribasic silicate in which the water is conceived to be substitutable 

 for any other monoxyde. 



The ittria was also tested optically for erbia with negative result. 



I am not aware that this material over the Gadolinite has been 

 named. I propose for it the name Metagadolinite. 



