6 EwiNG, The Structure of Metals. 



metal or in the crystallization of a salt from a solution 

 {Fig. 7, Plate IV), you see these branches actually being 

 formed. The process may be arrested before the inter- 

 mediate portions are filled up, but if it is allowed to 

 continue all the space would be filled up by the little 

 brickbats, and then we should have a structure in all 

 respects identical with that of the grains which are found 

 in a solid block of cast or forged metal. 



It may help you to think of the process as it actually 

 occurs in a metal if you picture to yourselves a number of 

 fairy children in a nursery provided with an unlimited 

 supply of little brickbats of the same shape and size. 

 Place the children in different parts of the nursery, give 

 each of them an ample supply of brickbats, and let them 

 all start building, not necessarily simultaneously (it does 

 not matter whether they do so or not), but let each start 

 building quite independently. Each places its first brick- 

 bat in some casual position without any reference at all 

 to the position in which the other children are placing 

 theirs, but once it has placed its first one it necessarily 

 places all the rest strictly parallel to it. That is essential 

 to the regular tactical formation of the crystal. Then 

 imagine the process to go on until the whole space in the 

 nursery is filled up. You will have each child's pile 

 determined in size and shape only by this consideration,, 

 how big does it become before it is stopped by coming 

 against the piles of its neighbours. That is exactly the 

 process of crystal building as we have it in metals. It is 

 casual differences in the rate of building one pile or 

 another that determines the irregular boundaries of the 

 grains. There is one further point to be mentioned. The 

 children of our analogue are as aggressive as European 

 powers in planting their flag in previously unoccupied 

 territory. The crystals do not simply progress as solids, 



