172 Mr White's New Method of Filtering Water. 



ready alluded to, I attached a half inch leaden pipe to a cistern, which was al- 

 ready fixed thirty-five feet above the ground-floor, where I placed the machine. 

 The other end of the pipe I made water-tight, by fixing it to a nozzle in the ap- 

 paratus, below a proper filtering-stone. Upon turning the cock A, which shuts 

 off the communication betwixt the machine and the cistern, the water rushed 

 down from the cistern with ^^reat force, and very sooli displaced all the air 

 contained in the apparatus through the pores of the stone S ; after which the 

 water began to ascend, and to flow in a filtered stream at the cock B, so as to 

 fill a gallon measure in about two minutes' time. Its appearance in small 

 bubbles, rising through every pore in the stone, from the great pressure of 

 the column of water contained in the small pipe P, suggested to me the name 

 which I have given it, of an artificial spring ; and further experience has 

 fully convinced me, that I have not applied to my invention an unmerited 

 title. From the construction of the apparatus, the sediment and aniraalculaj 

 will fall to the bottom, and be drawn off at the under cock C, and run off by 

 the waste-pipe E. In cases where several gallons are wanted at the same 

 time, and it might be inconvenient to wait uijtil it be filtered, shut the cock 

 B, leave A open, and in a few minutes, with a pressure fi-om a cistern of 

 thirty feet high, eight or ten gallons will be found filtered in the top part of 

 the apparatus, which can be drawn off" at B for immediate use, as required. 

 Should it filter more than the top reservoir contains, while A remains open, 

 it will run off" waste at F ; the cock A can be so constructed as to shut of its 

 own accord, but in this case the machine would not be so simple. The cock 

 A is of a peculiar construction, and well merits the attention of the reader : at 

 the same time that it shuts off the communication betwixt the machine and the 

 cistern, it opens, when turned one way, through the tube D, a small passage 

 to the atmosphere. By this contrivance, the filtered water in the top part of 

 the machine is allowed to subside the contrary way through the stone, a pro- 

 cess which must naturally tend to wash its pores clean ; and we know that 

 all filtering substances are subject to get clogged up, from particles of fine se- 

 diment lodging in their pores. But what back filtration does not remove in 

 my invention, another beautiful and simple phenomenon completely effects. 

 Open the under cock C, and then shut it again as fast as possible : this will 

 produce an immense pressure on the stone, and the water will be forced 

 through with so much rapidity as to clean its pores completely. From what 

 cause, I have not yet been able to ascertain, but it invariably happens, after 

 the process of forcing the air through the stone, that the power of filtration 

 is diminished considerably, and it is several hours before its power is restored. 

 It may be presumed that the air lodges in the pores of the stone, and shews 

 considerable obstinacy in being removed. When back filtration is not re- 

 quired, for it is only necessary for keeping the stone clean, the cock A must 

 be shut off, with the notch in the top of it towards the machine, and the fil- 

 tered water can be retained in the top part of the apparatus for any length of 

 time. Having briefly described the nature of my invention, it remains for 

 me to add, that it is an application of the Hydrostatic Paradox to the filtra- 

 tion of water, the nature of which admits of its being extended to any magni- 

 tude. For example, at the house where my first experiment was tried, the 

 altitude of the cistern was 35 feet, and the area of the stone contained 113 



