38 B. B. Biggs — Composition of Tourmaline. 



in establishing the fact that the iron in tourmaline is chiefly 

 ferrous oxide. Rammelsberg, following in his steps, afterwards 

 confirmed the results. But from what I can learn of their de- 

 terminations they involved a correction which is of such 

 a nature as to render the results worthless as quantitative 

 results. The decomposition being invariably incomplete, the 

 undecomposed material was removed from the glass tube, its 

 amount determined, and a correction made accordingly. 



3d. The mineral was also fused with bisulphate and with bi- 

 fluoride of potash respectively in an atmosphere of carbon 

 dioxide. Though decomposition was usually effected in a 

 couple of hours, the iron was invariably all oxidized. A reduc- 

 tion of the sulphuric acid may be the cause of the result when 

 bisulphate of potash was used. No such explanation avails 

 in the case of the bifiuoride fusion. 



4th. Convinced, by the summations of some of the analyses, 

 and by comparing the loss on ignition with the corresponding 

 direct water determinations, that the iron in tourmaline must 

 be there, in large part at least, in the ferrous condition, I 

 finally heated the mineral with hydrofluoric and sulphuric 

 acids in the closed platinum crucible over the direct flame, thus 

 digesting at a moderately high temperature and a correspond- 

 ingly high pressure, and at the same time securing a constant 

 agitation of the powdered mineral — a condition of vital im- 

 portance. In these determinations a thin lead washer replaced 

 the rubber. A half hour, with these conditions, usually suf- 

 ficed to bring about complete decomposition. The crucible 

 was cooled in an atmosphere of carbon dioxide and the iron 

 determined in the ordinary way with a permanganate solution. 

 Fair results were obtained, such as to indicate that the iron in 

 tourmaline is there chiefly in the ferrous condition. 



Alkalies. — Several vain attempts were made to decompose 

 the tourmaline with hydrofluoric and sulphuric acids. As show- 

 ing the refractory nature of the mineral the following is a case 

 in point : One gram of the pale green Auburn variety, after 

 being ignited, was evaporated to dryness with 20 c.c. of hydroflu- 

 oric acid five times, and yet left an insoluble residue of 0*473 

 grams. The Lawrence Smith method was finally adopted and 

 with highly satisfactory results. The only precautions neces- 

 sary are that the mineral be finely powdered and that the mix- 

 ture with ammonium chloride and calcium carbonate be inti- 

 mate, which latter condition is only to be secured by grinding 

 the several ingredients together. "When these conditions are 

 what they should be, there is no trouble in bringing about 

 complete decomposition in the course of an hour's gentle igni- 

 tion. After the alkalies have been leached out with water the 

 residue should of course be treated with acid to test the com- 



