678 Transactions. — Chemistry. 



^in. square, by contrasting it with the same kind of paper that 

 has not been so treated. A few short statements showing the 

 extreme tenuity of the gold in this paper may be interesting. 

 A square inch of the paper contains £^^gr., and ^jin. 



square contains ^oooooo g^- ^^ ?>'^^^- W^^'®. ^^^ 8°^^ .^^ ^^^^ 

 paper agglomerated to a film having a like area with that 

 of the containing paper that film would be only g-^^g^^^in. 

 thick — that is, 250 of these would be the thickness of gold 

 leaf. In the paper itself (being, as it is, yl^in. thick) this film 

 (of the sooooooo ^^-) ^^ broken up to occupy a volume 400,000 

 times that which it occupies in the form of a film.* 



It follows, therefore, that the gold in this paper, volume 

 for volume, only weighs half as much as hydrogen gas. 



Broken up in this manner in the test-paper before you, it 

 is in very truth fine gold — in fact, gold divided almost to its 

 ultimate atom (if, indeed, atoms do exist) — gold in the cloud 

 form, as it were, and therefore in the best condition that I 

 know of for my purpose. Provided with a test so delicate as 

 this is, we get results in an hour that, using the gravimetrical 

 test for loss, would require several days, and so we avoid those 

 errors that are apt to creep in and vitiate our results when 

 long periods of time are required for experiments of this 

 nature. 



Placing then in a porcelain vessel a strong aqueous 

 solution of cyanogen, along with a little of this gold test-paper, 

 I closed the vessel down airtight, and on examining at 

 periodic intervals I found that even after the expiration of six 

 hours, corresponding to sixty-two days for gold leaf, there was 

 no visible diminution of the colour of that test-paper. After 

 this, however, the tint gradually faded, until in thirty hours it 

 had quite disappeared. Thirty hours to dissolve the millionth 

 of a grain of gold so finely divided as this gold was, shows that 

 if cyanogen itself does dissolve gold it is only at an extremely 

 low rate — at such a rate that ordinary gold leaf would require 

 about one year to become entirely dissolved therein. 



Now, this result is a very different one to those that I am 

 faced with both by Professor Black and Mr. Park ; still, while 

 it is clearly shown that for gold-milling the gas cyanogen as a 

 direct solvent is useless, it does show that there is an infini- 

 tesimal dissolution of gold either by cyanogen or its deriva- 

 tives, and in the interest of exact science the question has to 

 be decided which of these it is. 



Now, the cyanogen I used, though very carefully prepared, 

 had a slight acid reaction ; it contained traces of ammonia, 

 hydrocyanic, and hydrochloric acids, and this even when 



♦ The method for accomplishing this is given in the " Transactions of 

 the New Zealand Institute," vol. xxv., p. 383. 



