REMARKS ON THE ALKALIES. 199 



matter of interest to know that from whatsoever locality it 

 comes this minute quantity of rubidium and caesium occurs 

 with it. On some future occasion I hope to be able to bring 

 together certain generalities in this connection of more or less 

 interest to mineralogists. 



I have also detected rubidium in half a gramme of margaro- 

 dite and Warwick mica, and have failed to detect it in apophyl- 

 lite, thomsonite, pectolite, elseolite, chesterlite, cancrinite, and 

 other silicates. 



Warwickite. 



This interesting compound has been known for some time 

 to American mineralogists, having been first described by Prof. 

 C. XJ. Shepard under the name of warwickite, and considered as 

 a hydrated silico-titanate of magnesia, iron, and alumina. It 

 was afterward described by Mr. T. S. Hunt under the name 

 of enceladite, and in his analyses (Amer. Jour, of Science and 

 Arts, 2d series, xi, 352) considered a trititanate of magnesia. 



In the re-examination of American minerals, in which Mr. 

 Brush and myself were engaged, this mineral came up in turn 

 for examination, and to our amazement it is found to contain a 

 large amount of boracic acid, doubtless upward of twenty per 

 cent. Approximative analyses are already made, but owing to 

 the difficulty of obtaining it of sufficient quantity in a perfect 

 state of purity, its final examination may be delayed for some 

 time ; and it is for that reason thought advisable to publish the 

 present note on the subject. It is essentially a borotitanate 

 of magnesia and iron ; the metallic acid, however, has some 

 anomalies about it not yet cleared up. This is the first boro- 

 titanate known, and as such highly interesting; the smallest 

 j)ortion of it when acted on with sulphuric acid will give the 

 strongest indication of the presence of boracic acid. 



