The consideration of the nature of this important element introduces to our notice one of the most original chemists of the eighteenth century—viz., the illustrious Scheele, who was born at Stralsund, in 1742, and in spite of every obstacle, fighting his "battle of life" with sickness and sorrow, he succeeded in making some of the most valuable discoveries in science, and amongst them that of chlorine gas. It was in the examination of a mineral solid—viz., of manganese—that Scheele made the acquaintance of a new gaseous element; and in a highly original dissertation on manganese, in 1774, he describes the mode of procuring what he termed dephlogisticated muriatic acid—a name which is certainly to be regretted, from its absurd length, but a title which was strictly in accordance with the then established theory of phlogiston; and if the latter is considered synonymous with hydrogen, quite in accordance with our present views of the nature of this element. Scheele discovered the leading characteristics of chlorine, and especially its power of bleaching, which is alone sufficient to place this gas in a high commercial position, when it is considered that all our linen used formerly to be sent to Holland, where they had acquired great dexterity in the ancient mode of bleaching—viz., by exposure of the fabric to atmospheric air or the action of the damps or dews, assisted greatly by the agency of light. Some idea may be formed of the present value of chlorine, when it is stated that the linen goods were retained by the Dutch bleachers for nine months; and if the spring and summer happened to be favourable, the operation was well conducted; on the other hand, if cold and wet, the goods might be more or less injured by continual exposure to unfavourable atmospheric changes. At the present time, as much bleaching can be done in nine weeks as might formerly have been conducted in the same number of months; and the whole of the process of chlorine bleaching is carried on independent of external atmospheric caprices, whilst the money paid for the process no longer passes to Holland, but remains in the hands of our own diligent bleachers and manufacturers.
First Experiment.
As Scheele first indicated, chlorine is obtained by the action of the black oxide of manganese, on "the Spirit of Salt," or hydrochloric acid; and the most elementary and instructive experiment showing its preparation can be made in the following manner:—
Fig. 130.
a. Flask containing the fuming hydrochloric acid, which is gently boiled by the heat of the spirit lamp. b. Tube passing to the Wolfe's bottle, containing pumice-stone or asbestos moistened with sulphuric acid. c. Second tube passing into a dry empty bottle, which receives the hydrochloric acid gas.
Place in a clear Florence oil-flask, to which a cork and bent tube have been first fitted, some strong fuming hydrochloric acid. Arrange the flask on a ring-stand, and then pass the bent tube either to a Wolfe's bottle containing some pumice-stone moistened with oil of vitriol, or to a glass tube containing either pumice or asbestos wetted with the same acid. Another glass tube, bent at right angles, passes away from the Wolfe's bottle into a receiving bottle. (Fig. 130). On the application of heat, the hydrochloric gas is driven off from its solution in water, and any aqueous vapour carried up is retained by the asbestos or pumice stone wetted with oil of vitriol; the application of the latter is called drying the gas—i.e., depriving it of all moisture; sometimes the salt called chloride of calcium is used for the same purpose, and it must be understood by the juvenile chemist that gases are not dried like towels, by exposure to heat, or by putting them in bladders before the fire, as we once heard was actually recommended, but by causing the gas charged with invisible steam to pass over some substance having a great affinity for water. The dry hydrochloric gas falls into the bottle, and displaces the air, being about one-fourth heavier than the latter, and gradually overflowing from the mouth of the vessel, produces a white smoke, which is found to be acid by litmus paper, but has no power to bleach, and is not green; it is, in fact, a combination of one combining proportion of chlorine with one of hydrogen, and to detach the latter, and set the chlorine free, it is necessary to convey the hydrochloric gas to some body which has an affinity for hydrogen. Such a substance is provided in the use of the black oxide of manganese, which is placed either in a small flask or in a tube provided with two bulbs, and when heated with the lamp it separates the hydrogen from the hydrochloric gas, and forms water, which partly condenses in the second bulb. And now the gas that escapes is no longer acid and fuming with a white smoke on contact with the air; but is green, has a strong odour, bleaches, and is so powerful in its action on all living tissues, that it must be carefully avoided and not inhaled; if a small quantity is accidentally inhaled, it produces a violent fit of coughing, which lasts a considerable time, and is only abated by inhaling the diluted vapour of ammonia, or ether, or alcohol, and swallowing milk and other softening drinks. (Fig. 131).
Fig. 131.
a. The flask containing the fuming hydrochloric acid, heated by spirit lamp. b. Tube passing to Wolfe's bottle, containing the pumice-stone or asbestos wetted with oil of vitriol. c. Second tube, which passes into a wide-mouthed small flask containing black oxide of manganese, partly in powder and partly in lump; and the third tube conveys the chlorine to any convenient vessel. The double bulb tube, e e, may be substituted for the flask, the oxide of manganese being contained in the bulb m.—N.B. Any tube may be joined on to another by a bit of india-rubber tubing, which is tied by string.