An Bjfay on Bleaching, %$$ 



moved by the application of potato. The alkali arifing from 

 the combuftion of plants is more powerful than the mineral 

 alkali, as 1 have already obferved. The alkaline fulphuret, 

 which is formed by the combination of fulphur and foda, is 

 far from poffemng fo deterfive a quality as that made with 

 potafh. 

 Various ProceJJes for Bleaching Hemp, Li?ien, and Cotton. 



Having already fpoken of the different methods hitherto 

 purfued Tor bleaching vegetable fub fiances, and examined 

 the menftrua and deterfive iubftances molt ufed in the va- 

 rious procefles, I (hall proceed to a defcription of the dif- 

 ferent manipulations to which thefe matters are fubje&ed 

 in order to give them that degree of whitenefs which is ne- 

 celfary to fit them for commerce. 



Bleaching in the open Air. 



The air with which the earth is furrounded is far from 

 being homogeneous. Every thing volatilized on the furface 

 of the globe; all the emanations of the earth, as well as the 

 beneficent fluids, which alfume the gafeous form, are con- 

 founded in this aeriform fea by which we are furrounded. It 

 is an immenfe laboratory always in action, where the play 

 of compofition and decomposition is incelfantly renewed. 



Of the numerous properties of the atmofpheric air, it will 

 be fufficient rf we mention only a few. About a fourth of 

 this fluid is compofed of a gas, which appears to be the acidi- 

 fying principle : this is oxygen, which readily fuffers itfelf to 

 be abforbed by a great number of bodies, among which are 

 carbon. This union with carbon forms carbonic acid, which 

 is alfo an aeriform fluid. 



Without calling in queftion thofe principles for which we 

 are indebted to modern chemiftry, mankind have at all times 

 employed free air as the moft convenient menftruum for 

 bleaching. When tired with the ftownefs of its action, they 

 aft] (led it by deterfive leys, which abridged the procefs a 

 little ; and this union of boiling, and expoiure on the grafs, 

 formed the whole of the antient art of bleaching. Formerly, 

 whew it was neceffary to bleach cloth, it was cuftomarv to 

 immerfe it in pure water to free it from the drefiing. This 

 preliminary operation was fometimes haftened by a cold lev, 

 the cloth was then rinfed in running water and fpread out on 

 a meadow, round which ran a dream of limpid water that 

 ferved for watering the different pieces. 



After being expofed in this manner for forne time, the 

 cloth was warned and boiled in a freih ley ; it was then again 



fpread 



