130 RE-EXAMINATION OF AMERICAN MINERALS. 



satisfy all doubts in this matter, Prof. Silliman, jr.,* examined 

 it with direct reference to the occurrence of phosphoric acid, 

 and in none of the specimens examined could he find more 

 than a trace. Subsequently Mr. Crossley,f of Boston, analyzed 

 it, and his results confirmed the previous analyses of American 

 chemists; meanwhile Hermann J re-examined it, and found the 

 phosphoric acid to vary in different specimens from 37.62 to 

 11.90 per cent, showing that he had not obtained a homo- 

 geneous mineral. 



Considerable pains have been taken to obtain a number 

 of authentic specimens for examination, some of which are 

 direct from the locality, and others from our own collection. 

 The results show that the mineral is a hydrate of alumina, 

 (XI H 3 ), with but a trace of phosphoric acid, and in some speci- 

 mens not even a trace existed. Two analyses gave 



1 2 



Alumina 64.24 63.48 



Peroxide of iron trace trace 



Water 33.76 34.68 



Silica 1.33 1.09 



Phosphoric acid .57 trace 



■•nesia .10 .05 



100.00 99.30 



The phosphoric acid was determined by molybdate of am- 

 monia; the small amount of silica is due to the intimate 

 mixture of the mineral with allophane. From the results of 

 these examinations we are confident that Mr. Hermann has 

 not at any time analyzed pure Gibbsite. 



26. Emerald Nickel. 



We notice in the last edition of Phillip's Mineralogy that 

 Professors Miller and Brooke place this species among the 

 doubtful ones, without, however, giving any reasons for so 

 doing. To ascertain if any good reason existed for this doubt 

 we have re-analyzed it, and find the same composition as given 

 by Professor Silliman, jr., which was 



Oxide nickel. Carbonic acid. Water. 



58.81 11.69 29.49 



*Amer. Jour. Science and Arts, 2d series, vii, 411. 

 tAmer. Jour. Science and Arts, 2d series, ix, 408. 

 X J- f- pr. Chem., xlvii, 1. 



