18 More about the day 



pure clay. Indeed no one has ever succeeded in making 

 clay out of bricks. All these experiments show that 

 clay is completely altered when it is burnt. We also 

 found that soil is completely altered by burning, and if 

 you look back at your notes you will see that the 

 changes are very much alike, so much so that we can 

 safely put down some of the changes in the burnt soil — 

 the red colour, the hard grittiness, and the absence of 

 stickiness — to the clay. Let us now examine a piece of 

 dry, but unburnt, clay. It is very hard and does not 

 crumble, it is neither sticky nor slippery. Directly, 

 however, we add some water it changes back to what 

 it was before. Drying therefore alters clay only for the 

 time being, whilst baking changes it permanently. 



