BLEACHING. 



583 



Bleaching, temperature. Hence, when equal parts of salt, man- 

 * v ' ganese, and diluted sulphuric acid, are used in 'the 

 distillation of the oxymuriatic acid, the residuum ta- 

 ken from the retort is uniformly found to be super- 

 sulphate of soda combined with manganese. The 

 quantity of manganese used is also too great, and 

 much of this substance is wasted, no more being ne- 

 cessary than is sufficient fully to oxygenise the mu- 

 riatic acid during the distillation. 



At the same time, it is proper to remark, that the 

 proportion of manganese must be subject to variation 

 according to its quality. 



Mr Rupp of Manchester ( Trans, of the Lit. and 

 Phil. Soc. of Manchester, vol. v.) recommends, man- 

 ganese 3 parts, common salt 8, sulphuric acid 6, water 

 12. The bleachers in the neighbourhood of Glasgow 

 commonly use equal parts of salt, manganese, sulphu- 

 ric acid, and water, as mentioned above. In Ireland, 

 the common proportions are said to be, manganese 

 6 parts, common salt 6, sulphuric acid 5, water 5. 

 In France and Germany, we understand, they vary 

 little from the following : manganese 20 parts, com- 

 mon salt 64, sulphuric acid 44, water 51. 



Besides the above methods of making the oxymu- 

 riatic acid, that which was originally introduced by 

 Mr Berthollet has again been used by several bleach- 

 ers, on account of the higli price of potash. It con- 

 sists of introducing one part of oxide of manganese 

 into the retort, on which is poured two parts of mu- 

 riatic acid, of the specific gravity of 1200, which is 

 diluted with its bulk of water. 



The reason given by those who have again resorted 

 to the latter process for making this acid, is, that 

 one-half of the quantityof alkali is sufficient for neu- 

 tralizing it in the receiver, because the oxymuriatic 

 acid gas is presented in a pure state without any mix- 

 ture of sulphureous acid gas, which they suppose is 

 always produced by a part of the sulphuric acid be- 

 ing decomposed in the retort by the impurities mixed 

 with the oxide of manganese ; and that, in conse- 

 quence, one-half of the alkaline lixivium is sufficient, 

 no more alkali being necessary than a sufficiency to 

 retain the oxymuriatic acid gas in a proper state of 

 neutralization for the purposes of bleaching. What- 

 ever of theory may be in these inferences, it is cer- 

 tain, that bleaching liquor made in this manner pos- 

 sesses power equal, if not superior, to any in use, for 

 rendering goods white expeditiously. 

 Distillation We shall now describe the preparation of the oxy- 

 cf the oiy- muriatic acid combined with potash, as conducted in 

 the apparatus invented by Mr Fisher. See Plate LVI. 

 Fig. 4-. 



Supposing the receiver K to contain 120 gallons 

 English wine measure, it is filled at the hole M with 

 a solution of caustic potash of the specific gravity of 

 1015; the lead 6topper is then replaced. Twen'ty- 

 onc lbs. of common salt being intimately mixed 

 with fourteen lbs. of the black oxide of manga- 

 nese, the mixture is moistened with water, and 

 wrought together until it is of the consistence of 

 moist dough. By this means, the salt, in a state of 

 solution, unites more intimately with the manganese. 

 The top of the retort being removed, the salt and 

 manganese are put into it ; the cover is then replaced, 

 and firmly screwed on its place. 



add. 

 Plate 

 LVI. 

 Fig. -1. 



Into 16 lbs. of sulphuric acid pour gradually the Bleaching, 

 same weight of water, and allow the mixture to cool. - 



One half of the diluted acid is poured, by a lead fun- 

 nel, into the retort by the hole at C, which is then 

 closed by the lead plug to prevent the escape of the 

 oxymuriatic acid gas which is instantly disengaged, 

 after which a violent agitation is heard in the receiver 

 K. The distillation is usually begun in the evening, 

 and the workman, after seeing the operation going 

 properly forward, leaves it to work of itself. In the 

 morning, the distillation having abated, the remainder 

 of the diluted sulphuric acid is poured into the re- 

 tort, when a fresh disengagement of the gas takes 

 place. As soon as it is observed to slacken, a fire is 

 put into the furnace in order to heat the boiler B, 

 which is filled with water, into which chaff or any 

 similar light substance is put to prevent the evapora- 

 tion of the water. By the increased heat of the wa- 

 ter, the distillation goes forward with renewed vigour ; 

 and the fire is continued until no more gas is disen- 

 gaged, which is known by the bubbling noise in the 

 receiver being no longer heard. The oxymuriatic acid 

 combined with potash may now be drawn off by the 

 stop-cock N from the receiver for use. 



In the above process, the sulphuric acid having a 

 greater affinity for the soda contained in the common 

 salt than that which the muriatic acid has, the latter 

 is disengaged from the soda, and, acting on the man- 

 ganese, it deprives it of its oxygen, which now exist- 

 ing in the state of oxymuriatic acid ga3, by its ex- 

 pansive force is impelled forward through the tubes 

 G and I into the receiver K, where it is absorbed by 

 the caustic alkaline solution. 



V. No farther improvements seem to have taken OxynniH 

 place in the combination of this acid with any other r ' ate of 

 substance than the alkalis until the year 1798, when mne " 

 Mr Charles Tennant of Glasgow, by a well conduct- 

 ed series of experiments, shewed, that it was capable 

 of being united with what are called the alkaline 

 earths, such as barytcs, strontites, and lime. Lime 

 being most readily procured, after a number of trials 

 he found, that, by mechanical agitation, and in con- 

 sequence of the suspension of the finer particles of 

 the lime in water, it readily united with the oxymuri- 

 atic acid gas, and was thereby completely dissolved. 

 When, therefore, a sufficient quantity of finely pul- 

 verised quicklime is put into the receiver K in place 

 of potash, and mechanically agitated during the dis- 

 tillation of the oxymuriatic -acid, it will be found that 

 it is entirely dissolved, and forms a pure and transpa- 

 rent solution of oxymuriate of lime, possessing the 

 same power of retaining the gas as the alkalis do. 



Mr Tennant has since carried this improvement to 

 a greater degree of perfection, by combining the oxy- 

 muriatic acid with quicklime in the dry way, and 

 thus rendering it portable to any distance at a small 

 expence. For this further improvement he justly re- 

 ceived another patent, which secures him the exclu- 

 sive right of this valuable manufacture. This disco- 

 very is of great importance, as, by means of so com- 

 mon and cheap a substance as lime, great savings are 

 made by the bleacher in the expence of alkali ; and 

 this improvement may not improperly be called a 

 new era in the history of bleaching. 



For use, the concrete oxymuriate of lime is diffused 



