CHLORINE 789 



chloride of gold is then conveyed through a trough lined with sheet-lead into the 

 precipitating-vat, which is a large wooden vessel lined with lead or with asphalt. To 

 precipitate the gold, a solution of sulphate of iron (green copperas) is employed ; 

 this is best prepared a few days before use, by pouring dilute oil of vitriol on old 

 pieces of wrought iron. A bucket or two of this solution is poured into the precipita- 

 ting-vat before the gold-solution enters, and a sufficient quantity is afterwards employed 

 to throw down the whole of the gold. This precipitated gold gradually subsides as a 

 dark brown powder, and the supernatant liquor when clear is drawn off. The gold is 

 then carefully scooped out from the vat into a clear porcelain dish, and the last traces 

 washed out by water. This finely divided gold is dried over a fire, and then melted 

 in clay crucibles ; a little borax, salt, or saltpetre being added as a flux. The use ot 

 phimbago crucibles is not advisable. The metal obtained in this way generally con- 

 tains about 995-thousandths of pure gold. F.W.B. 



CHLORINE. (Chlorine, Fr., Chlor, Ger.) Symbol, Cl. ; Atomic weight, 35'5. 

 This element was discovered by the Swedish chemist, Scheele, in 1774, and its true 

 elementary character demonstrated by Sir H. Davy in 1810. It exists, under ordinary 

 circumstances, as a greenish-yellow gas; but, when exposed to a pressure of 4 

 atmospheres, at 60 F., it condenses to a transparent liquid, which remains unfrozen 

 even at the cold of 220 F. In the first state, its density, compared to air (reckoned 

 1-00), is 2-47; in the second, its density, compared to water (I'OO), is 1-33. It is 

 generally obtained either by the action of sulphuric acid on a mixture of common salt 

 and binoxide of manganese, or by the action of moderately strong hydrochloric acid on 

 binoxide of manganese alone. In the first case, the proportions are 7 parts by weight 

 of oil of vitriol, previously diluted with 7 parts of water and 4 parts of common salt, 

 intimately mixed with 3 parts of binoxide of manganese ; in the latter, which is the 

 most convenient method, hydrochloric acid, specific gravity 1-15, is gently heated with 

 the finely-powdered binoxide, in the proportions of about three oz. of oxide to half a 

 pint of acid. The hydrochloric acid should not be more diluted than above indicated, 

 otherwise an explosion may occur, probably in consequence of the formation of one of 

 the explosive oxides of chlorine. The gas must be collected either over brine or over 

 warm water. 



In the preparation of chlorine from binoxide (peroxide) of manganese and hydro- 

 chloric acid, 43'5 parts by weight of manganese and 73 of acid yield 35'5 parts of free 

 chlorine. If the peroxide of manganese be acted on by a mixture of hydrochloric and 

 sulphuric acids, 43 - 5 parts of the manganese, 36-5 of hydrochloric and 49 qf sulphuric 

 acid, will produce 35'5 of chlorine gas. When the generating materials are common 

 salt, sulphuric acid and peroxide of manganese, 58'5 parts of salt, 147 of acid, and 

 43'6 of manganese yield 35'5 of chlorine. In this case a bisulphate or acid sulphate 

 of soda remains in the retort, but if the supply of acid should only be sufficient to 

 form a neutral sulphate the complete decomposition will not be effected until a much 

 higher temperature has been reached than was required with the larger proportion of 

 acid. With respect to the calculations given above, it should be remaiked that they 

 refer only to theoretical reactions with pure materials, and that in practice the manu- 

 facturer will find it necessary to use more than the specified quantities of acid in order 

 to allow for combination with lime, oxide of iron, and whatever other bases may be 

 present as impurities in the raw materials. 



In addition to the ordinary methods of generating chlorine already described, several 

 others have been proposed for obtaining this element from its combinations, chiefly 

 from hydrochloric acid. Some of these methods work with the hydrochloric acid in 

 the state of gas. For example, the gas may be caused to act directly upon peroxide of 

 manganese ; or it may be mixed with carbonic acid gas, and the mixture transmitted 

 through red-hot earthenware tubes ; or again a mixture of hydrochloric acid and the 

 gases evolved by heating nitrate of soda may be similarly treated. In all these cases an 

 oxidising agent is employed to remove the hydrogen from the hydrochloric acid and 

 thus liberate the chlorine. The simplest method of effecting this oxidation is to pass 

 hydrochloric acid gas and atmospheric air over red-hot pumice-stone or asbestos or 

 spongy platinum. A somewhat similar process has lately been ingeniously devised by 

 Mr. Henry Deacon, of the Widnes Alkali Works, and has been successfully worked on 

 a manufacturing scale. A mixture of hydrochloric acid gas and atmospheric air, 

 heated to from 700 to 750 F., is passed over a mass of brick-work which has been 

 soaked in a solution of sulphate of copper (blue vitriol) and dried. Under these cir- 

 cumstances the oxygen of the air and the hydrogen of the acid unite to form water, 

 while the chlorine is liberated, mixed of course with the nitrogen of the atmospheric 

 air, but this dilution of the chlorine does not prevent its employment in the manufacture 

 of chloride of lime. The action of the copper salt in this process is rather obscure ; 

 many other salts are capable of playing a similar part, and their action is supposed to 

 be merely catalytic, that is to say, they induce the reaction between the oxygen and 



