STUPIDITAS. _We have never known such failures to take place as you
describe. In all probability you have not_ perfectly _immersed your paper
in the saline solution. Half a drachm of muriate of soda, and the same
quantity of muriate of barytes and muriate of ammonia, dissolved in a quart
of water, forms a very excellent application for the paper, previous to the
use of the ammonio-nitrate._
H. HENDERSON. _Any application applied to your window would in a great part
obstruct the light. Brushing it over with starch might be tried._
B--Z. _Yes. Many of the very best pictures in the_ Photographic Exhibition
in Bond Street, _as we may probably take an opportunity of pointing out in
some future notice of that interesting collection, are from collodion
negatives._
PRICE OF IODIDE OF POTASSIUM. _I beg to say that the price named by me_,
i. e. 1s. 3d. _per oz., for iodide of potassium, is quoted from the list of
Messrs. Simpson and Maule, Kensington Road._