Intelligence and Miscellaneous Articles. 73 



below. As the land steadily rises these mud-beds are elevated 

 above the sea. The coast is fringed with the ice-foot, forming a 

 flat terrace 50 to 100 yards in breadth, stretching from the base of 

 the cliffs to the sea-margin. This wall of ice is not made up of 

 frozen sea-water, but of the accumulated autumn snowfall, which, 

 drifting to the beach, is converted into ice where it meets the sea- 

 water which splashes over it. 



2. " On the Pabeontoiogical results of the recent Polar Expedition 

 under Admiral Sir George rTares, K.C.B., F.R.S." Bv Capfc. H. ^Y. 

 Feilden, E.A., F.G.S., and Robert Etheridge, Esq., F.R.S., F.G.S. 



XI. Intelligence and Miscellaneous Articles. 



AMMONIO-ARGENTIC IODIDE. BY M. CAREY LEA. 



Y¥THEN silver iodide is exposed to ammonia-gas it absorbs 3-6 per 

 * * cent., and forms, according to Hammelsberg, a compound in 

 which an atom of ammonia is united to two of AgT. Liquid ammonia 

 instantly whitens Agl; every trace of the strong lemon-yellow 

 colour disappears. The behaviour of the ammonia iodide under 

 the influence of light differs singularly from that of the plain 

 iodide, and will be here described. 



The affinity of Agl for ammonia is very slight. Tf the white 

 compound be thrown upon a filter and washed with water, the 

 ammonia washes quickly out, the yellow colour reappearing. If 

 simply exposed to the air, the yellow colour returns while the 

 powder is yet moist ; so that the ammonia is held back with less 

 energy than the water. So long, however, as the ammonia is pre- 

 sent, the properties of the iodide are entirely altered. 



Agl precipitated with excess of KI does not darken by exposure 

 to light even continued for months. But the same iodide exposed 

 under liquid ammonia rapidly darkens to an intense violet-black, 

 precisely similar to that of AgCl exposed to light, and not at all 

 resembling the greenish-black of AgT exposed in presence of excess 

 of silver nitrate. (This difference no doubt depends upon the 

 yellow of the unchanged Agl mixing with the bluish-black of the 

 changed, whereas in the case of the ammonia iodide the yellow 

 colour has been first destroyed.) 



When the exposure is continued for some time, the intense 

 violet-black colour gradually lightens again, and finally quite dis- 

 appears; the iodide recovers its original yellow colour, with perhaps 

 a little more of a greyish shade. This is a new reaction, and differs 

 entirely from any thing that has been hitherto observed. It has 

 been long known that darkened Agl washed over with solution of 

 KI and exposed to light, bleached. This last reaction is intelli- 

 gible enough ; for Klin solution exposed to light decomposes, and 

 in presence of Agl darkened by light gives up iodine to the Agl, 

 and so bleaches it. The above experiment is quite different. The 

 darkened substance may be washed well with water (during which 



