156 



are taken to prevent loss of heat by conduction, this high temperature 

 can be produced by the ordinary blowpipe operating upon flames of this 

 description. 



Art. XXXIV. — -On the Application of Iodine and Bromine, for the detection 

 of Gold when in minute quantities. By W. Skey, Analyst to the 

 Geological Survey of New Zealand. 



{Read before the Wellington Philosophical Society, November 13, 1869.] 



The large number of non-auriferous, or but slightly auriferous, specimens of 

 quartz and pyritous rocks, which have lately been submitted here for examina- 

 tion for gold, has rendered it very desirable that some quicker, less laborious, 

 and, if possible, more exhaustive, method of analysis, than the current one 

 (that by amalgamation), should be employed. 



In recognition of this I have frequently been urged by the Director of this 

 Department to attempt some other process, and after several preliminary 

 experiments I turned my attention, especially, to the use of iodine or bromine 

 for this object. 



Both of these substances differ from chlorine especially in their relatively 

 feebler affinities for hydrogen, so there would be the less to fear, that from the 

 generation of hydra-acids, any great preponderance of other matters would be 

 dissolved along with the gold we wish to separate from the sample under 

 examination. 



Iodine, indeed, has already been used with advantage in the analysis of 

 certain meteorites, for the separation of the iron and nickel existing therein in 

 a metallic state ; these it combines with, leaving the associated silicates, iron- 

 oxides and sulphides intact. 



It was this comportment of iodine with other substances, that determined 

 me to the trial of both it and bromine for the purpose named. 



The results of my experiments certainly show that either of these agents 

 may be safely and advantageously employed for the separation of gold from 

 its matrices. 



The following are the particulars of a few of these experiments, which 

 besides their present use, will, I think, be iiseful in showing what is, 

 approximately, the smallest quantity of gold that can be positively separated 

 and identified, by a certain course of analysis operating upon a limited quantity. 

 The first time, I believe, anything of this kind has been attempted. 



1st. 2 grammes of roasted " buddle headings" from a quartz mine at the 

 Thames, known from previous analysis to contain gold at the rate of one ounce, or 

 so, to the ton, was well shaken for a little while with its volume of alcoholic solu- 

 tion of iodine (tincture of iodine, of chemists), then allowed to subside. A piece of 

 Swedish filter-paper was then saturated with the clear supernatant liquid, and 

 afterwards burned to an ash ; the ash, in the place of being white, as it would 

 be if pure, was coloured purple ; the colouring matter was quickly removed by 

 bromine — a clear indication of the presence of gold. The time occupied by the 

 whole process was twenty minutes. 



2nd. 1 gramme of the same "buddle headings," mixed with such a quantity 

 of soil as to reduce the proportion of gold present to 2 dwts. per ton, was allowed 

 contact with its volume of the tincture for two houi'S, with occasional stirring ; 

 a piece of filter-paper was then saturated with the tincture, and dried, five 

 times consecutively, and finally burnt off as before ; in this case, also, the 

 colour of the residual ash was purple, and it gave the reaction of gold. 



3rd. 32 grammes of siliceous hematite, finely -pounded, was thoroughly mixed 

 with precipitated gold to the amount of 2 dwts. per ton ; then ignited, and 



