20 



What lime does to clay 



The muddy liquid obtained by shaking clay with 

 water clears quickly if a little lime is stirred in. Fill 

 two jars A and B (Fig. 10) with rain water, rub clay 

 into each and stir up so as to make a muddy liquid, 

 then add some lime water to B and stir well. Leave for 

 a short time. Flocks quickly appear in B, then sink, 

 leaving the liquid clear, but A remains cloudy for a long 

 time. But why should the liquid clear? We decided 

 in our earlier experiments that the clay floated in the 

 water because it was in very tiny pieces ; when we took 

 a larger lump the clay sank. The lime has for some 

 A 



No lime added Lime added 



Fig. 10. 



Addition of lime to turbid clay water now makes 



the clay settle and leaves the water quite clear 



reason or other, which we do not understand, made the 

 small clay particles stick together to form the large 

 flocks, and these can no longer float, but sink. If we 

 look at the limed clay in our funnel experiment we shall 

 see that the same change has gone on there ; the clay 

 has become rather loose and flufiy, and can therefore no 

 longer hold water back. 



Lime also makes clay less sticky. Knead up one 

 piece of clay with rain water alone and another piece 



