M. C. Lea—Ammonia-argentic Lodide. 379 
ing around the basal segments of the first pair. leon six- 
jointed; uropoda short, biramous, each ramus two-jointed, the 
outer more slender than the inner, half its length and bearing 
a long bristle at the tip. Length 25mm. - | 
This species was taken along with P. dimicola and unfortu- 
nately only a single specimen is as yet known, 
Yale College, April, 1878. 
Art. LVL.—Ammonio-argentic Iodide ; by M. Cary Lexa. 
WHEN silver iodide is exposed to ammonia gas it absorbs 
3°6 per cent, and forms Bets to Rammelsberg a compound 
in which an atom of ammonia is united to two of Ag] Liquid 
ammonia instantly whitens AglI, every trace of the strong lemon- 
yellow color disappears. The behavior 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 AgI for ammonia is very slight. If the 
white compound be thrown upon a filter and washed with 
water, the ammonia washes quickly out, the yellow color re- 
appearing. If simply exposed to the air, the yellow color 
returns while the powder is yet moist, so that the ammonia is 
held back with less energy than the water. So long, however, 
e€ ammonia is present, the properties of the iodide are 
entirely altered. 
Agl precipitated with excess of KI does not darken by ex- 
posure to light even continued for months. But the same 
iodide exposed under liquid ammonia rapidly darkens to an 
intensé violet-black, precisely similar to that of A 
to light, and not at all resembling the greenish-black of Agi 
exposed in presence of excess of silver nitrate. (This differ- 
ence no doubt depends upon the yellow of the unchanged AgI 
mixing with the bluish-black of the changed, whereas in the case 
of the ammonia iodide the yellow color has been first destroyed.) 
the exposure is continued for some time, the intense 
violet-black color gradually lightens again, and finally quite 
disappears, the iodide recovers its original yellow color with 
perhaps a little more of a grayish shade. This is a new reac- 
tion and differs entirely from anything that has been hitherto 
observed. It has been long known that darkened AglI washed 
over with solution of KI and exposed to light, bleached. This 
ast reaction is intelligible enough for KI in solution expo 
washed well with water (during which operation it passes 
