592 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



Barium and strontium were looked for in the precipitated calcium oxalate after 

 ignition, and estimated by the method given by Bunsen in his treatise on Mineral 

 Water Analyses; the purity of the resulting compounds of these elements was ascer- 

 tained by means of the spectroscope. 



When a rock was examined merely to ascertain the presence or absence of 

 barium, a considerable portion (10 grams) was decomposed with hydrofluoric and sul- 

 phuric acids, the soluble salts were extracted with water after expulsion of the hydro- 

 fluoric and excess of sulphuric acids, the residue was fused with sodium carbonate, 

 extracted with water, and the insoluble part collected on a filter. After solution in 

 hydrochloric acid, the barium, if present, was thrown down with sulphuric acid, the 

 precipitate ignited and weighed, and after decomposition with sodium carbonate, tested 

 spectroscopically.^ 



For the estimation of the alkalies, decomposition was effected in the earlier anal- 

 yses by hydrofluoric and sulphuric acids; in the later by heating in a platinum cruci- 

 ble with calcium carbouate and ammonium chloride. The potassium was thrown down, 

 after weighing the mixed chlorides, as potassium-platinic chloride, and calculated from 

 the weight of the latter, the sodium being found by difference. Lithium could never 

 be detected spectroscopically in the potassiumplatinic chloride, but occasionally iu 

 the sodium salt. 



Chlorine was determined by fusing with alkaline carbonate, extracting with 

 water, acidifying the filtrate with nitric acid, and precipitating with silver nitrate. 



Phosphorus pentoxide was always determined in a separate portion of the pow- 

 der, and water by ignition in a hard glass tube and absorption in a weighed calcium 

 chloride tube. The loss in weight by treatment with acid in a suitable apparatus gave 

 the carbon dioxide. 



For the detection and estimation of lead, large quantities (30-50 grams) were 

 employed. Pyrite and other soluble salts were first extracted with nitric or niiro- 

 hydrochloric acid; the filtrate, together with copious washings, evaporated nearly to 

 dryness several times with nitric acid ; the residue digested with dilute nitric acid, 

 and the solution and undissolved matter separated by filtration. As the insoluble 

 part might contain a trace of lead sulphate, a warm ammoni.ical solution of ammonium 

 tartrate was passed repeatedly through the filter, and to the filtrate ammonium sul- 

 phide added. Through the previous nitric acid solution a strong current of hydrogen 

 sulphide gas was passed for a considerable length of time, the precipitate, mainly sul- 

 phur from reduction of iron salts, collected on a filter, well washed, dried, and ignited 

 gently with the filter paper to volatilize the sulphur. A few drops of nitric acid were 

 then added, and heat was applied to dissolve the lead, mostly reduced to the metal- 

 lic state by the carbon of the filter paper. The solution was filtered onto a watch- 

 glass, and to this was added the nitric acid solution of any lead sulphide that might 



' Later investigation by the writer seems to indicate that baryta may be a far more frequent con- 

 stituent of eruptive roclis than has hitherto been supposed. The failure to detect it in the ignited cal- 

 cium oxalate, where it is usually looked for, cannot bo regarded as a proof of its absence from the erup- 

 tive rock examined. Experience in a number of cases has shown that where baryta and lime are in 

 solution in as high a proportion as 1 of the former to 4 or 5 of the latter, in presence of considerable 

 ammonium chloride, an almost complete separation of the two is effected by double precipitation of the 

 lime by ammonium oxalate. The solubility of barium oxalate appears to be increased by the presence 

 of magnesium salts. An ordinary spectroscope repeatedly failed to show the faintest evidence of barir.m 

 in the ignited calcium oxalate. This subject will be more fnlly investigated. (W. F. H.) 



