P. E. Browning — Analysis of Rhodochrosite, 375 



*• 



Aet. XLYII. — Analysis of Rhodochrosite from Franklin 

 Furnace, New Jersey ; by P. E. Beownjjstg. 



The specimen of rhodochrosite, an analysis of which is here 

 given, was collected for the Yale Museum some two or three 

 years since and was furnished to writer for examination by Pro- 

 fessor E. S. Dana. It has a massive, cleavable structure and a 

 bright pink color. Franldinite and willemite are immediately 

 associated with it. The method of analysis was, as follows : 



A portion, of the mineral was dissolved in hydrochloric acid, 

 evaporated to dryness to separate any silica present. The 

 filtrate from silica was treated either with sodic acetate or 

 ammonium hydrate and the iron separated and weighed. After 

 the separation of the iron, the zinc was precipitated as sulphide 

 by hydrogen sulphide in acetic acid solution. The filtrate 

 from sulphide of zinc was treated with bromine water, by 

 which method the manganese comes down as black oxide. In 

 two determinations ammonia was used with the bromine water 

 to bring about the same result. In all these cases the black 

 oxide was dissolved and reprecipitated to avoid any holding 

 back of lime. The black oxide in every case was dissolved by 

 sulphurous and hydrochloric acids, precipitated as phosphate 

 and weighed after ignition as pyrophosphate according to 

 Gibbs's method. The amount of manganese being large, two 

 direct determinations were also made by Ford's method, which 

 consists in boiling the mineral, after separating the silica, with 

 strong nitric acid and potassium chlorate until green fumes 

 cease to be given off. The black oxide is thus directly pre- 

 cipitated and may be treated as above by Gibbs's method. 

 These results were satisfactory in their agreement. The filtrate 

 from black oxide of manganese was evaporated to about 300 

 or 400cm 3 , made ammoniacal, and calcium precipitated as 

 oxalate, dissolved and reprecipitated in same manner. The 

 filtrate from both oxalate precipitations was evaporated (and 

 in two cases the residue was ignited to free it from great 

 excess of salts of ammonia) and precipitated as phosphate, dis- 

 solved in hydrochloric acid, and reprecipitated in same manner 

 with ammonia and a little hydrodisodic phosphate, ignited and 

 weighed as pyrophosphate. Each element was determined at 

 least three times. Five determinations of manganese were 

 made. Two analyses of the mineral were carried through in 

 platinum dishes to avoid any contamination by silica in glass 

 or porcelain. The amount of iron in ferrous condition was 

 determined by dissolving a portion of mineral in sulphuric 



Am. Jour. Sci. — Third Series, Vol. XL, No. 239. — Nov., 1890. 

 24 



