188 GEOLOGICAL RECONNOISSANCE 



METHODS OF ANALYSIS. 



■o- 



In the following pages, I propose giving a short exposition of the 

 methods employed in the analysis of the ores and rocks described in this 

 Report; not for the purpose of serving as a guide to those engaged in 

 similar investigations, but merely to furnish those who are able to judge 

 with a scale, by which to measure the reliability of the results. For this 

 reason, I shall forbear entering into details, and confine myself to giving 

 a general outline. 



SMITHSONITE, 



Impurities: insoluble silicates; iron; alumina, lime; magnesia. 



I. The pulverized mineral is treated with hydrochloric acid, the solution 

 evaporated to dryness over a water-bath, residue treated with dilute 

 hydrochloric acid, and insoluble silicates collected on filter. 



II. The filtrate is oxidized with nitric acid, excess of acid partly 

 removed by evaporation, solution nearly neutralized with carbonate of 

 soda, then iron and alumina precipitated with carbonate of baryta; pre- 

 cipitate collected on filter, dissolved in dilute hydrochloric acid, baryta 

 removed by sulphuric acid, and iron and alumina precipitated with 

 ammonia; the ignited and weighed precipitate is dissolved in hydrochloric 

 acid, the solution reduced with metallic zinc, and the iron determined 

 volumetrically with chamaelon mineral. 



III. The filtrate from the treatment with carbonate of baryta is precipi- 

 tated with sulphuric acid, to remove baryta, the solution neutralized with 

 ammonia, and precipitated with sulphhydrate of ammonia; liquid with 

 precipitate allowed to rest (in a well-stoppered bottle) for about 24 hours, 

 sulphuret of zinc collected on filter, washed with water containing sulph- 

 hydrate of ammonia, dissolved in hydrochloric acid, and precipitated with 

 a hot solution of carbonate of soda (from the washings, traces of zinc 



