The Phosphates of America. 1G1 



warmed, and reduced with pure zinc until no coloration is produced 

 when a drop of the liquid is brought into contact with a drop of 

 potassium-sulphocyanate solution. 



It is then cooled, and titrated with -| N permanganate solution, 

 until the faintest possible pink color remains constant for two 

 minutes. Every c.c. of the permanganate employed = .0056 Fe 

 in one gramme of the ore. 



Copper. 



Five grammes of the original sample are treated with concen- 

 trated nitric acid, and evaporated to dryness. The residue is 

 treated with concentrated sulphuric acid ; heated on a sand-bath 

 till the free acid is all driven off ; and then cooled, treated with 

 water, boiled, cooled again, finally treated with one-fourth its 

 volume of alcohol, and allowed to stand for twelve hours and 

 filtered. The residue on the filter is washed three times with a 

 mixture of one part alcohol and two parts water, and the dilute 

 filtrate is then saturated with hydrogen sulphide and allowed to 

 stand for some hours. The precipitated sulphides are washed 

 with a solution of H 2 S ; dissolved in aqua regia ; neutralized 

 with an excess of ammonia ; and made slightly acid again with 

 hydrochloric acid. If not clear, the solution is then filtered, and 

 the filter well washed until no longer acid. 



The solution is now boiled ard treated with 25 c.c. of a strong 

 mixture, containing equal weights of potassium sulphocyanide and 

 sodium bisulphite. The addition is made by degrees and with 

 constant stirring, and, when completed, the beaker is removed from 

 the fire and allowed to stand until quite cold, when the white pre- 

 cipitate of copper sub- sulphocyanide will have all gone down. 

 The liquid is now filtered carefully through a double-tared filter, 

 and the precipitate is well washed several times, first by decanta- 

 tion with cold water in the beaker, and finally on the filter. The 

 washing is complete when all traces of chlorides have disappeared, 

 and the precipitate is then thoroughly dried in the gas-oven. 

 When perfectly dry it is weighed, the tare of the double filter 

 is deducted from the weight, and the balance X .- gJ V 3JL = Cu in one 

 gramme of the ore. 



