360 Transactions. — Chemistry. 



by native iridescent minerals is caused by the action of thin 

 films of matter upon light — in fact, by what is termed inter- 

 ference. In order, therefore, to beautify with colour where 

 nature had stopped at form, it was necessary to find an inso- 

 luble substance, unaffected by either air or moisture, but at the 

 same time transparent, and capable of attaching itself firmly 

 in smooth coherent films on those minerals which are the 

 best reflectors of light. 



It gives me great pleasure to inform you that my efforts 

 in this direction have been completely successful, as may be 

 seen by an inspection of the exhibits on the table. I shall 

 now proceed to place before you the results of my investiga- 

 tions. 



While experimenting with hyposulphite of copper for 

 another purpose, I observed that a portion of the cupric sul- 

 phide whicli I had precipitated therefrom by heat had 

 attached itself in a continuous transparent film to the vessel 

 containing the solution. The idea of utilising such films for 

 chromatic purposes at once suggested itself, and I accordingly 

 plunged various fragments of metallic sulphides into the boil- 

 ing solution of cupric hyposulphites, and was gratified to find 

 that in a few minutes they had all become enfilmed to such an 

 extent as to appear in the sunlight of a ruby-red colour. I 

 also found that by longer immersion all the colours of the 

 spectrum could be obtained. 



The films producing these colours, even while wet, were 

 found to adhere to the sulphides so tenaciously as not to be 

 removed w'ithout the aid of solvents. To test the cohesion of 

 the film as applied to galena, I gummed a piece of paper on to 

 it, dried it thoroughly, and then tore it off forcibly, without 

 the least injury to the film. In the case of stibnite similarly 

 treated, inuch of the film came off with the paper. On this 

 account I am inclined to think that the surfaces of the galena 

 had chemically united with the inner surface of the cupreous 

 film, thus forming a compound sulphide. 



To produce the very best effects with these films it is 

 necessary to operate upon the fresh surfaces of opaque 

 crystals, as these are the most highly reflective of any mineral 

 surface that we know of. So far as I have yet pushed my 

 experiments, the best minerals to use for this purpose are 

 arseno-sulphide of nickel, misiDickel, galena, and stibnite. 



Specimens of the last two, both in their natural and 

 artificially-coloured states, are on the table. The more 

 lustrous of our cokes also take on a very brilliant green. 



After repeated experiments for other substances capable 

 of forming adherent films on glass or native minerals, I find 

 that the following do so as precipitated from alkaline hypo- 

 sulphites : sulpho-arsenide of silver, sulpho-arsenide of coj)per, 



