Chapter C: B. (Birmingham). If the hyposulphite of soda is not thoroughly

removed from a Photograph, it will soon become covered with reddish spots, and in a short time the whole picture may disappear. If cyanide of potassium has been used, it is requisite that the greatest care should be used to effect its removal entirely._

W. L. (Liverpool). _A meniscus lens of the diameter of four inches should have a focal length of twenty inches, and will produce perfect landscape pictures fourteen inches square. It is said they will cover fifteen inches; but fourteen they do with great definition. We strongly advise_ W. L. _to purchase a good article. It is a bad economy not to go to a_ first-rate _maker at once._

J. M. S. (Manchester). _You will find, for a screen to use in the open air, that the white cotton you refer to will be far too light. "Linsey woolsey" forms an admirable screen, and by being left loose upon a stretcher it may be looped up so as to form drapery, &c. If you cannot depend upon the collodion you purchase in your city, pray use your ingenuity, and make some according to the formulary given in_ Vol. vi., p. 277., _and you will be rewarded for your trouble._