156 
Mr Herschel on the Hyposidphurmis Acid. 
metallic mercury. The action of water resolves this, as is well 
known, on a super and sub salt. The crystals being ground in 
a glass-mortar with repeated effusions of distilled water, the 
powder preserved its brilliant whiteness till the third or fourth 
affusion, when suddenly,* while grinding and mixing it with 
fresh water, it passed to a sombre greenish-yellow hue, almost 
in an instant. I continued to grind it, and the colour height- 
ened ; but, to my great surprise, having desisted a few moments, 
my attention being taken off, I found, on resuming the grind- 
ing, that the yellow-green colour had again disappeared, and 
the powder had passed to a light ash-grey, almost white, and 
seemed to have become rather more bulky and crystalline. In 
its chemical properties it had undergone no change, dissolving 
readily, as I had expected, in dilute nitric acid, and affording a 
solution similar in all respects to that obtained by water in the 
course of the washing and grinding. 
As the quantity operated on was rather considerable (perhaps 
2 oz.), and the change of colour simultaneous over the whole 
mass, there is little doubt of a sudden subversion of equilibrium 
and a new arrangement of the molecules accompanying this phe- 
nomenon, though why it should take place at this precise epoch, 
seems difficult to explain, the abstraction of the acid having 
been going on gradually from the beginning. 
Slough, \ 
Nov. 1819. 1 
Art. XXIX .— of a Mlneralogical Journey through 
Souths North and East Iceland by Mr John Menge of 
Hanau f. In a Letter addressed to Professor Jameson. 
At the foot of the Eyafialla-Jokulls, I satisfied myself that 
the Westmanna Islands, which are eighteen English miles from 
* We regret that want of time forces us to delay the map illustrative of Mr 
Menge’s route, until our next Number. — E d. 
•j* Mr Menge embarked at Copenhagen for Iceland on 19th May 1819, and 
reached the Westmanna Islands, off Iceland, on 9th June. After a short stay 
there, he landed on Iceland, and proceeded to Reikiavig, examining the country as 
he went along. From Reikiavig, he crossed the whole island to Skagafiord, a jour- 
