556 
SUMMARY OF CURRENT RESEARCHES. 
The metal surface is smeared with the cement and then pressed on the 
glass, the superfluous cement being removed with some suitable instru- 
ment. The cement dries very quickly and becomes very hard. 
Blackening Finely Polished Brass.* — (1) Dip in copper-vitriol 
solution, allow to dry, and then immerse in solution of sodium sulphide : 
bright blue-black film of copper sulphide. 
(2) Smear with thin solution of mercuric nitrate, then (after drying) 
with sodium sulphide solution, causing a bright black deposition of 
mercury sulphide. 
(3) Gold chloride and metastannic acid dissolved hot, then applied 
to the metal. 
Photographic Developer.! — Herr E. Merck states that pyrocatechin 
sublimatum is increasing in popularity as a developer, as it keeps well 
in solution, is simple and easily manipulated, and quickly produces 
pictures of great clearness and distinctness. The following solution is 
recommended as a developer : — water 1000 ccm. ; crystallised sulphite 
of soda 25 ccm. ; crystallised carbonate of soda 50 ccm. ; pyrocatechin 
10 ccm. 
Tauxe’s Photographic Paper.! — Prof. J. Amann calls attention to 
a new paper made by Tauxe of Lausanne, which he has found to possess 
great advantages for scientific and especially for photomicrographic 
photography. The finest details of the negative are faithfully and 
vigorously reproduced. No special treatment is required for copying, 
toning, or fixing. The copies may be retouched, written on, or painted 
with ink, Indian ink, water- and oil-colours, without any trouble. 
* Cent. Zeit. f. Opt. u. Mech., No. 6, 1899, p. 55. 
t Zeitschr. f. angew. Mikr., v. (1899) p. 24. 
X Zeitschr. f. wiss. Mikr., xv. (1899) p. 445. 
