CAPILLARY SIPHONS. 253 



Expt. 298. To Empty a Basin of Water by means of a 

 Hank of Cotton. If a porous substance, such as a piece of calico, 

 be hung so that one end dips in water, the water will gradually 

 travel upwards and wet the whole of the piece ; the ascent of the 

 oil in the wick of a lamp or of the melted tallow or wax in the 

 wick of a candle is due to this action, which is substantially the 

 same as that of the ascent of a fluid in a fine capillary tube 

 (Expt. 296). 



If a piece of lampwick, a twisted towel, a hank of cotton, or 

 similar material be hung over the side of a basin of water so that 

 one end is in the water and the other hangs over outside, water 

 will be found to drip down from the outside end, being gradually 

 raised out of the basin by this wick-like action. In this way, a 

 wineglass full of water may be gradually emptied without touch- 

 ing it by placing a prawn or shrimp on the rim so that the tail 

 end is inside the glass and the head outside. If the water in a 

 basin be turbid from the presence of a little fine clay or other 

 suspended matter, it may be filtered perfectly clear whilst passing 

 through the " Capillary Siphon " formed in this way by a hank 

 of cotton, &c. ; but if it be coloured by some soluble coloured 

 substance this will usually not be abstracted from the water by 

 the passage through the siphon. 



If, however, the capillary siphon be made of white wool (pre- 

 viously dipped in water and wrung out), and certain kinds of 

 dyestuffs be dissolved in the water, the wool will in many cases 

 remove these from the water whilst passing through, so that the 

 water dripping down at the far end will be colourless or nearly so, 

 whilst the wool itself becomes more or less tinted or dyed. This 

 kind of action is sometimes exerted to a small extent upon 

 dissolved substances by paper. If a drop of a solution of a 

 coloured salt (such as sulphate of copper, or perchloride of iron) 

 be carefully placed on a piece of white blotting-paper, it will 

 " run " and produce a circular wet spot. If another drop be 

 placed in the centre of this the circle will extend ; and by repeat- 

 ing the process a wet circle of a couple of inches or more in 

 diameter may be produced. In many cases it will be found that 

 the outermost rim of this wet circle is colourless, consisting of 

 paper wetted with little but plain water, the dissolved solid having 

 been mostly removed from the solution by passing along the porous 

 paper fibres from the centre outwards ; so that whilst the central 

 part of the wet spot is highly coloured, the outer edges are colourless, 

 or at any rate much less strongly tinted. If the outermost edge 

 be marked off with a pencil and the paper dried in a horizontal 

 position (over a hot plate, &c.) it will often be visible that the 



