* 
CB; Himes— Preparation of Photographic Dry-Plates. 17 
gallic acid developer, is about the same as that of ordinary 
tannin plates, whilst the results are perhaps more certain, and 
the negatives cleaner. 
The principal advantages of the preceding method lie in the 
complete division of the operations. The plates can be brought 
to the tanninizing stage leisurely, and comfortably, at any 
time, in an ordinary well-lighted and well-ventilated room; an 
the confinement to the dark room, with its damp and unhealthy 
them with ammonia, as in the ordinary paper | eens process, 
show that it possesses a decided sensitizing effect, but that the 
ness under development with the pyrogallic acid developer, 
after exposure in the camera; and those fumed for the longest 
time, as well as those for the shortest time, were less sensitive 
than those acted on for an intermediate length of time. In 
the process recently suggested. by Krone, the operations are 
also conducted in daylight, the effect of which is prevented in- 
of removed. This is accomplished by taking advantage 
of the well known fact, that argentic iodide, formed in the 
aie of excess of potassic iodide, is insensitive to aght, 
ut may be rendered sensitive. The plates are coated with a 
collodion containing argentic nitrate, and immersed in a bath 
of potassic iodide, or in some cases of potassic iodide and 
bromide, and are then washed, and dried, and subsequently 
sensitized with argentic nitrate solution. Organic matter is 
added to all the solutions, including the collodion, in the form 
Am. Jour. Sc1.—Tatrp VIII, No. 48.—Juty, 1874. 
2 
