160 BLEACHING. 



time tojine (or become transparent), by depositing 

 the mucilage that was suspended in it. When 

 there is time, the beer is allowed to fine itself; if 

 not, a preparation of isinglass and sour beer, called 

 finings, is put into it, to precipitate the mucilage. 



A larger quantity of hops are used in porter than 

 for ales. Although in porter the brown malts are 

 necessary, it is bad economy to use them too highly 

 dried for the deepening of the colour, since the 

 consequence of drying too highly is a carbonization 

 of part of the saccharine matter. A dark colour 

 may be procured more economically by adding 

 burnt sugar to the wort. 



It is in Britain prohibited by law to use any sub- 

 stance in brewing, as a substitute for hops. 



BLEACHING. 



Bleaching is the art of whitening cloths, made 

 from vegetable or animal substauces, by depriving 

 them of their colouring matter. The art is of 

 great antiquity; and mankind, in all ages, appear 

 to have admired garments of a pure whiteness. The 

 effects produced by the air and rain upon, vegetable 

 fibres exposed to them, must have led originally to 

 the idea of producing this by artificial means. The 

 ancients appear to have been acquainted with the 

 uses of soap and leys ; and to have practised bleach- 

 ing, nearly in the same manner as it existed among 

 us until lately. But few manufactures have received 

 so much benefit from modern chemistry, as that 

 now under consideration ; so that since the year 

 1786, it has undergone a complete change. 



Bleaching of Linen. 



The processes of bleaching differ materially, 

 according to the different materials of which cloths 



