CHEMICAL SCIENCE. 181 



which is stated to be of great advantage from its accuracy, and from 

 the ease and facility with which it is conducted. It is based, he says, 

 upon the decoloration of an aminoniacal solution of copper, by fine 

 cyanide of potassium or sodium, or ammonia, or hydrocyanic acid, in a 

 free state ; but I prefer to use cyanide of potassium, as being less sub- 

 ject to decomposition, and more readily obtained in a state of purity in 

 commerce than the other substances named. 



The method of operating is as follows : Take a given quantity of 

 pure copper, (say, for instance, 13 grains,) place it in a flask, and dis- 

 solve in nitric acid ; add ammonia in excess, and then make it into a 

 bulk of about 2500 grs. by measure by the addition of water, although 

 this is not absolutely necessary. Dissolve 1 oz. (Avoirdupois) pure 

 cyanide of potassium, free from ferro-cyanide or sulphuret of potassium, 

 iu 5 ounces by measure of water, filter, if necessary, and place the solu- 

 tion in a well-stoppered bottle, till required for use. I then ascertain the 

 quantity of this solution of cyanide of potassium required to decolorize 

 the solution of copper by taking a given quantity, in any graduated 

 vessel, as a burette, and pour it by degrees into the solution of copper, 

 adding the last quantity drop by drop till decolorized. This is very 

 easily perceived, as there is no precipitate to interfere ; and the opera- 

 tion is conducted at the ordinary atmospheric temperature. I mark 

 down the quantity required (say 500 grains by volume.) After having 

 established this date, it is very easy to estimate the quantity of copper 

 contained in any ore or cupriferous product, by simply dissolving a cer- 

 tain quantity, (say 20 grains in nitric or nitro-muriatic acid,) with the 

 assistance of heat, if required, as in the case of some sulphurets the 

 addition of ammonia in excess is necessary ; and if any considerable 

 quantity of iron, or alumina, was present in the sample, it should be 

 allowed to digest at a gentle heat, under ebullition, to make sure that 

 all the copper is taken up by the ammonia ; filter into a flask, wash the 

 precipitate with water, and make into a bulk of 2500 grains, as when 

 taking the standard of the solution of pure copper. All that now re- 

 mains to be done is to allow it to get cold, and add the cyanide of 

 potassium, until decolorized, noticing the quantity taken. I will sup- 

 pose it required 400 grains by volume of the cyanide solution ; then 

 from the proportion 500 grs.KCy. : 10 Cu. : :"K Cy. 400 : Cu. 8 

 the quantity of copper contained in the 20 grains of material taken for 

 analysis, or 40 per cent. If the ore taken was a sulphuret, it is some- 

 times advisable to filter, in order to separate the sulphur, before adding 

 the ammonia, or else to use a dilute solution of ammonia, and a gentle 

 heat when digested, or small particles of sulphuret of copper might be 

 re-produced, especially when the precipitate produced by the ammonia 

 is a bulky one. 



When manganese is present in the ore easily ascertained by pre- 

 liminary examination by the blow-pipe it is best to employ carbonate 

 of ammonia ttf form the ammoniacal solution, as the carbonate of man- 

 ganese is very little soluble in this re-agent. The reason for this 

 modification is, that, on adding cyanide of potassium to an ammoniacal 

 solution of copper containing that metal, it assumes a slightly yellow- 



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