186 GEOLOGICAL RECONNOISSANCE 
METHODS OF ANALYSIS. 
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. 
Il. 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 chamezlon mineral. 
Ill. 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 
