The book of lantern ; being a practical guide to the working of the optical (1888)

42 THE BOOK OF THE LANTERN. best substance for the purpose is caustic soda, or potash, Failing this, common washing soda will answer nearly as well. Caustic soda is rather an awkward thing to travel about with, for it is of a most corrosive nature ; but it should be used in preference to anything else, when gas is made at home. Fragments of disused lime cylinders will also answer well. To show that the chlorine is actually taken up by the bag and its belongings, I may mention that if the experi- ment be tried it will be found that the gas when first made, although highly charged with chlorine and inducing coughing and other unpleasant sensations if inhaled, may, after having been left in the bag for an hour or two, be breathed without any ill effect. Mr. Fleuss, whose diving and life-saving apparatus de- pends in a great measure upon a supply of compressed oxygen gas, called my attention to the above fact, and told me that he had used gas for breathing purposes which had been freed of its chlorine by remaining in the gas bag for some hours as I have just explained. I may mention that the residue left in the retort—and which I have recommended, should be washed out without delay,—consists of chloride of potash, and the manganese; the latter quite unaltered. It may be useful to point out that the difference between the chlorate and the chloride is easily seen by examining the crystals of each under a microscope. If a little chlorate mingled with water is placed on a slip of glass, and allowed to evaporate, the crystals will have a rhombic form (see A, fig. 19). But if, on the other hand, a solution of chloride of potash be examined