28 



SEEDS AND SEEDLINGS. 



But the area of the water-column increases as the squares of the 

 diameters of the tubes (area of a circle = '785 X square of diameter), 

 hence the wider tube will only lift its column one-tenth as high as 

 the narrower one, its load being then ten times as great. 



Fine tubes that show this phenomenon well are called capillary 

 (i.e. hair-like) lubes, and the phenomenon is known as capillarity. 

 The " soaking up " of ink by blotting-paper is an example of capillary 

 attraction, the fibres of the blotting-paper being really minute tubes, 

 whose substance is "wetted" by the ink, so that the level of the liquid 

 rises considerably in the tubes. Other cases are the "sucking up" of 

 water by a lump of sugar, the rising of the melted wax in the wick of 

 a burning candle or of oil in a lamp-wick, and the diffusion of water 

 through soil 



51. Osmosis. When raisins are placed in water, they swell up 

 just as dry seeds do. On the other hand, if grapes are placed in 

 a strong solution of sugar, they shrink. The swelling of the dried 

 seeds or raisins and the shrinking of the fresh grapes are due to osmotic 



If we place in a vessel of water a bladder filled with a strong solution 

 of a substance having an "attraction" for water, e.g. sugar, a large 

 amount of the water will diffuse (pass by osmosis) into the bladder 

 (endosmosis), while a small amount of the solution will diffuse out 

 (exosmosis). The weaker solution diffuses faster, and this continues 

 until the same concentration is acquired, when it is equally rapid 

 in both directions, and hence apparently ceases. Meanwhile pressure 

 is set up inside the bladder, owing to rapid endosmosis. 



* 52. Thistle-tube Experiments. (a) Get a thistle- tube ("thistle- 

 funnel," with 18-inch tube, 3d. or 4d.), and 

 prepare a strong (about 10 per cent.) solution of 

 sugar, colouring it by adding red ink if the 

 experiment is to be shown in a class. Get a 

 butcher to clean, inflate, and dry a sheep's 

 bladder for you ; cut out a piece large enough to 

 tie over the wide mouth of the tube, and soak 

 it in water. 



Plug the narrow end with a bit of plasticine, 

 pour into the wide end enough solution to 

 fill the head and an inch or so of the narrow 

 part, tie over the mouth the piece of bladder, 

 invert the funnel, and remove the plug of 

 plasticine. Then fix the "funnel," head down- 

 wards, into the cork of a wide-mouthed glass 

 jar containing water, so that the coloured sugar 

 solution in the tube is level with the water 

 (Fig. 16A). Observe the rise of the liquid in the 

 tube of the funnel, also show that a little of the 

 sugar solution diffuses into the water, by evapora- Flg - 16 - 



ting the liquid in the dish to dryness, when a 

 small residue of sugar will remain. If the sugar solution used is strong 



