328 SCIENCE AND FRUIT GROWING 



of the beneficial action of frost consists in breaking down the 

 large clods by mechanical disruption, due to expansion on the 

 freezing of the water contained in them : but it also affects the 

 ultimate particles themselves, and it was found that its action 

 on them consisted in depriving them of the chemically combined 

 water which they contained. The result of this is a shrinkage 

 of the particles, which thereby become more dense, and at the 

 same time agglomerate together, in consequence of which they 

 subside more rapidly, forming a more compact sediment. This 

 action was found to be common to all bulky substances contain- 

 ing a large amount of combined water, and the shrinkage observed 

 in different cases varied between 40 and 90 per cent. With 

 clay it amounted to 80 per cent., and was found to be the same as 

 that occurring when the clay was deprived of its combined water 

 by long exposure over sulphuric acid before being puddled with 

 water. 



Clay, and such substances, after they have been dehydrated 

 by freezing, or other means, do not appear to be able to re-absorb 

 the water which they have lost, even when they are left in con- 

 tact with water for a long time; yet such re-absorption must 

 occur somehow under the conditions in the field. 



