282 J. E. Whitfield — Natural Borates and Borosilicates. 



hydrochloric acids, in an atmosphere of carbonic acid, heating 

 to a temperature of about 100° C. in a tightly sealed platinum 

 vessel, devised and used expressly for such determinations. 

 When the mineral was thoroughly decomposed, which is gene- 

 rally the case after standing twelve hours with occasional 

 shaking, the solution was titrated with permanganate of potas- 

 sium. This method is undoubtedly superior to that employed 

 by Rammelsberg and Tschermak in their analyses. The direct 

 estimation of the water was made, after drying the mineral at 

 104° C, with the apparatus devised by Dr. Gooch,* by which 

 the errors caused by calculating the water from ignition and 

 oxidation of the ferrous iron are eliminated. The silica in 

 every case has been corrected by evaporation with hydrofluoric 

 and sulphuric acids and the residue added to the precipitate of 

 iron and alumina. 



Colemaxite, from Death Valley, California. — Of this min- 

 eral there were put at my disposal two specimens very different 

 in appearance. One of them, designated as A, was a large, 

 transparent crystal of the ordinary type, to all appearances per- 

 fectly clear and free from impurities. 



By analysis the following resuhs were obtained, and I insert 

 for comparison the analysis by Mr. J. T. Evansf and the theo- 

 retical composition calculated from the formula given below : 

 A. J. T. Evans. Theory. 



H 2 21-87 21-835 21-9 



B 2 3 50-70 50-990 50-9 



' CaO 27-31 27-175 27-2 



MgO -10 



99-98 1UO-000 100-0 



The molecular ratios from analysis A are CaO : B 2 8 : H 2 — 2 r 

 3 : 5 — resulting in the simple formula 2CaO . 3B 2 8 . 5H a O, the 

 calculated composition of which does not differ much from the 

 results of the analysis. Mr. Evans calculated the same formula 

 from his analysis in which the boric acid was determined by 

 difference. 



The second specimen, B, was from the same locality, but 

 was in the form of a deposit implanted on gangue, and con- 

 sisted of small blade-like crystals, almost white, but in some 

 lights appearing of a greenish cast. Two analyses yielded the 

 following result : 



B. 



1. 2. 



H 2 22-66 22-70 



B 2 3 49-56 49-62 



CaO 27-36 27-40 



MgO -25 -26 



Si0 2 . -44 47 



100-27 100-45 



* Am. Chem. Jour., ii, 247, 1880. f Proc. Cal. Acad. Sci., No. 1. 



