Pyrogallic acid and soda carbonate solutions will not keep many minutes; decomposition sets in directly the two are brought together. The pyro solution (No. 1) prepared with nitric acid and a small quantity of w-ater will keep good for several months, but the acid should be added first. Sulphite of soda may also be added to the pyro as a preservative, as follows. Take 8oz. of sulphite of soda (a fresh sample should be used, as after slight exposure to air it becomes sulphate and is useless) and dissolve in 30 oz. of hot water to which has been added twenty drops of nitric acid, the soda solution (No. 2) maybe prepared by dissolving fioz. of washing soda in 30oz. of water. For use, take 1 oz. each of No.l and No. 2 and add 3oz. of water. This is sufficient for a whole plate. When using the alum solution, fill the dish to within about tin. >>i the brim; this may be used till it becomes discoloured (say for live or six plates). The same quantity of fixing solution will fix three or four plates.

It is not advisable to use it for a greater number, because the hypo becomes charged with silver and does not do its work so rapidly nor so well.