Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/692

and in cases of tetanus it is employed to produce muscular relaxation, Its antagonism to strychnia was first pointed out by Liebreich (Gompt. rend., 1870, Ixx. 403). When administered to rabbits it has been found to be a remedy for poisonous dosss of strychnia (Bennett, Edin. Med. Journ., 1870, xvi. 262); but Ore" has shown (Gaz. Medic, de Paris, 1872, p. 401) that the hypodermic injection of that drug is of no avail in the case of rabbits poisoned with fatal doses of chloral hydrate. Numerous experi ments have led to the conclusions that " chloral hydrate is more likely to save life after a fatal close of strychnia, than strychnia is to save life after a fatal dose of chloral hydrate ; " that after a dose of strychnine has produced tetanic convulsions, these convulsions may be reduced in force and frequency, and life may be saved, by means of the influence of chloral hydrate ; but that though the effects of a poisonous dose of the hydrate may be mitigated, the coma produced by its action an the brain is not removed by strychnia (Bennett, Report in Brit. Med. Jour., 1875, 1, 97; Ogiivie Will, Edin. Med. Jour., April 1875, 907). Chloral hydrate modifies the action of a fatal dose of extract of Calabar bean, but is of little service if given some time after the latter. The effects of chloralism are

combated by provoking emesis, and by stimulating freely.

Among the very numerous contributions to the history of chloral, in addition to the above-given, may be mentioned the following : Liebig, Ann. Ch. Pharm., i. 189; Dumas, Traitede Chimic, t. v. 599 ; Stadeler, Ann. Ch. Pharm., cv. 293, cvi. 253 ; Bouclmt, Gompt. rend., Ixix. 966, Bull, de Ther., Ixxvii. 433 ; Sir J. Y. Simpson, Med. Times, Jan. 1, 1870; Byasson and Follet, Journ. de I Anat. ct de Physiol, 1870, 570; Hofmann, Compt. rend., 1870, Ixx. 906; Personne, ibid., Ixxi. 227; Paul, Pharm. Journ. and Trans. (3), i. 621 ; Hausemann, Schmidt s Jahrb., cli. 81 ; Jacobsen, quoted in Journ. Chem. Soc., ix. 257; Eokitansky, Strieker s Jahrbuchcr (iii. and iv. Heft), 1874.

(p. h. b.)

CHLORINE, one of the chemical elements (symbol, Cl), discovered by Scheele in 1774. It was long regarded as a compound ; Scheele termed it defthlogisticated muriatic acid, and Berthollet about 1785 gave it the name of oxygenized muriatic acid, which Kirwan contracted into oxymuriatic acid. In 1809 an abstract of a paper was published by Gay-Lussac and Thenard, in the 2d vol. of the Memoires d Arcueil, in which they demonstrated the possibility of the absence of oxygen from oxymuriatic acid. The atten tion of Davy being drawn to the subject, he in 1810 com municated to the Royal Society a paper in which he showed that there was no evidence in support of the opinion that oxymuriatic acid contained oxygen ; and in a paper published in the following year he comes to the conclusion that oxymuriatic acid is an uncompounded substance, and gives to it the name of chlorine, on account of the greenish colour it possesses. Chlorine and its combinations with other elements having been already treated of under the heading Chemistry, it will be necessary here only to give some account of the more important commercial chlorine compounds hydrochloric acid, bleaching powder, and potassium chlorate, and of the methods of preparing them.

Hydrochloric Acid (HC1).—Practically, the whole of the hydrochloric acid now employed in the manufacturing arts is obtained as a collateral product in the celebrated soda process of Leblanc. The first stage in that process consists in treating common salt with sulphuric acid in the salt-cake roasting furnace, by which sodium sulphate and hydrochloric acid are formed:—2NaCl + H 2 SO 4 ? Na i> S0 4 + 2HC1.

Till the year 1863 the acid fumes given off in alkali works were allowed to escape freely into the atmosphere, and being dissolved and brought down by every shower, destroyed or seriously damaged vegetation for miles around the works. In that year the Alkali Act was passed, by which manufacturers were obligsd to condense not less than 95 per cent, of the total amount of hydrochloric acid evolved in their establishments ; and since that time great attention has been paid to the condensation, so that now in many works practically no acid fumes escape. The hydrochloric acid gas liberated in the roasting furnace is conveyed through a range of stoneware pipes, in connection with which are various devices for cooling it in its passage. It is then conducted into condensing towers—long wide funnels packed with coke—through which a stream of water is made to percolate from the top, an enormous surface of moisture being thus presented to the acid fumes. The solution of the gas in the water constitutes the hydrochloric acid, muriatic acid, or spirit of salt of commerce. So prepared, the acid always contains several impurities, such as arsenious acid, ferric chloride, and sulphurous acid ; but these do not interfere with its application to the prepara tion of bleaching powder, in which it is chiefly consumed. Without any purification it is also employed for " souring " in bleaching, and in tin and lead soldering.

Bleaching Powder, or Chloride of Lime.—The history of the application of chlorine to bleaching purposes before the introduction of the so-called chloride of lime will be found under the article Bleaching. Bleaching powder is made by exposing pure slaked lime to an atmosphere of chlorine till the lime will absorb no more of the gas. Many plans for the preparation of the chlorine have been proposed, and various important processes adopted, since the manufac ture of bleaching-powder was established by Messrs Tennant and Co. The original process was as follows. A mixture of native peroxide of manganese ground to a fine powder, common salt, and sulphuric acid was put into a large, nearly spherical, leaden vessel furnished at the top with an air-tight lid. In this vessel an agitator was placed by which its contents could be from time to time stirred up. From the lid a lead pipe conveyed the liberated chlorine into the chamber in which the lime to be saturated was spread in a thin layer. The exterior of the leaden vessel was cased with an iron covering, space for the circulation of a current of steam between it and the covering being left. Upon the charging of the still chlorine was at first given off without heat ; but after some time a current of steam was made to circulate around the still, so as to maintain a sufficient temperature to disengage all the chlorine. The materials used consisted of common salt, manganese peroxide, and sulphuric acid, and the resulting products were manganous sulphate, sodium sul phate, water, and chlorine:—

Mn0 2 + 2NaCl + 3H,SO 4 = MnS0 4 + 2NaHSO, + 2H 2 + C1 2 .

Through the development of Leblanc s well-known soda process large quantities of hydrochloric acid became available for the manufacture of chlorine, in place, as formerly, of a mixture of common salt and sulphuric acid ; and for many years hydro chloric acid alone has been used. Coarsely ground manganese oxide is placed within an oblong stone still, into which the necessary charge of strong hydrochloric acid is admitted. Steam is then allowed to circulate in the outer case of the still till the temperature of the mixture is raised to about 180 Fahr. When this point is reached, steam at a pressure of 20 to 25 lt>. is blown through the charge at intervals for about six hours, after which the reaction is complete the whole occupying about twenty-four hours. The chemical changes that take place are expressed in the following equation:—

MnO s + 4HC1 = MnCL, + 2H 2 + Cl s .

Native binoxide of manganese being an impure and variable com pound has to be used in quantities proportionate to the 31n0 2 it contains.

For each molecule of chlorine obtained by the above reaction, it will be observed that one of manganous chloride is foiTned, a sub stance that was formerly run off as a waste product. Apart from the nuisance thereby created, the drain on the supply of manganese ore became serious, supplies diminished, and prices rose in proportion. It became therefore an object of much importance to obviate the waste of manganese, and this was sought in two different directions.