IMBIBITION 



537 



{il) Elect roclioin'ra] (idsorplloii. Prepare three sdliitions of :i dve, one in 

 each of three test tubes as follows : 



1. lOc.c. of dye + 1 c.e. N . 1 1. SO, 



2. 10 c.c. of dye + 1 c.c. water. 



n. lOe.c. of dye + 1 c.c. N . NaOll. 



I^it a strip of filter paper into each tube. In a few minutes, iciiiove the 

 papers and wash them in cold water. Only one paper is periiianently stained 

 — which paper depends on the dye used. 



Dyes to try (all 0-01 per cent.). Methylene blue, crystal violet, brilliant 

 green, night blue, Nile blue, and (O-Oo per cent, solution) Congo red, and 

 Ol per cent, ponceau GR. 



Note tliat this type of adsorption is irreversible. 



39. Imbibition. 



(a) Allow a sheet of ordinary glue to lie overnight on a moist surface so 

 that the under portion of the glue alone is in contact with water. Note 

 the increase in volume of the immersed ]Jortion and also the alterations in 

 colour, opacity, elasticity, etc. 



(6) X strip of thin sheet rubber (dental or patching rubber) about 

 12 in. X Ih in. is cut almost its whole length into two fingers of equal width. 

 One of the divisions is immersed in a boiling tube filled with benzol, while the 

 other half is left hanging outside. In a few minutes the immersed division 

 imbibes benzol and swells so that it is at least half again as long and as broad 

 as the unimmersed division. 



(c) Effect of the dielectric value of the imbibed fluid on the amount of swelling. 

 Cut a number of exactly similar strips of dental rubber, say, 6 in. x h in., 

 and suspend one in each of the following fluids in test tubes : Water, ethyl 

 alcohol, acetone, amyl alcohol, benzol, toluol, xylol. Examine and measure 

 the strips after about half an hour. It will be found that the rubber has not 

 swollen in the water, slightly in the ethyl alcohol, and so on, till the largest 

 increase is found in xylol. That is, the power of imbibition varies inversely 

 as the value of the dielectric constant (q.v.). 



{d) (i.) To show that imbibed fluid is held under compression. Tie a short 

 piece of surgical laminaria tanga to the stem of a hydrometer (near the 

 foot). Float in water and note the level. After some hours, again read 

 the hydrometer scale. If the water imbibed is not under compression both 

 readings should be the same (see experiment on p. 97). 



(ii.) Pressure by CEdometer (Fig. 22, p. 98). Place two large teaspoonfuls 

 of Cox's powdered gelatin in the foot of the cylindrical glass container. 

 Re])lace the plunger and attach the indicator clip. The pointer should be 

 adjusted to read zero. Add sufficient water to reach two-thirds up the 

 cylinder. When the apparatus is examined next day it will be obvious from 

 the drop of the pointer on the scale that the gelatin has swelled. The scale 

 may be calibrated to give readings in cubic centimetres. Repeat the experi- 

 ment, adding weights to the balance pan. For example, the addition of a 

 weight of 1 kilo slows the rate of imbibition, 2 kilos slows it still further, and 

 so on. till with a certain weight, say, 30 kilos, the swelling is inappreciable. 



Swelling of Gelatin in Water. 



Pressure (mm. Hg.) 



Grams HgO per gram of gelatin 



40 

 2-5 



80 

 2-0 



156 



1-5 



240 

 1-3 



303 

 11 



377 



0-9 



