VARIETIES OF CHARCOAL FILTERS. 



Ill 



pipe which conveys it to the upper part of the second filter, 

 placed close by. Thus it continues through the whole 

 series, until it is at last drawn off by a cock placed for the 

 purpose in the last vessel. Each of the cylinders is 6 feet 

 high, and three feet in diameter. Three of them would be 

 required in a boiling-house making 3 hhds. a day. They 

 act well for about five or six days. The charcoal is never 

 removed from them, but when its powers require to be 

 restored, boiling water is introduced for the purpose of 

 washing away as much as possible the syrup remaining in 

 the interstices. The sweet liquid which comes away is 

 thrown into the evaporating vessels, w T hile the filters are 

 put into some warm place, that fermentation may ensue. 

 It is stated that this fermentation is completely terminated 

 after 24 or 36 hours. In this way the organic matters 

 which had neutralized the decolourating powers of the char- 

 coal are destroyed, and to restore its properties, nothing 

 more is required but an effective washing. This is best 

 performed by the injection of high pressure steam for half- 

 an-hour. When steam is not used in the boiling-house, hot 

 water must be passed through in a continued stream until 

 it comes away clear and limpid." Dr. Evans also describes 

 the following simple method of making a filter, which can 

 be easily constructed in any boiling-house : — " Take a clean 

 rum puncheon, and at the distance of two or three inches 

 from the bottom, make a support sufficient to retain a 

 piece of basket-w r ork, corresponding in size to that part of 

 the cask. Into the space between this and the bottom, 



