but oak is not more expensive than birch. It is because oak splits lengthwise, while birch is not easily split, but is made of tough filaments.
Accordingly, though oak has a closer texture than birch, it is so constituted that it splits, while birch is not easily split.
Why are the rims of the wheels and the bounds bent from oak or elm, but never out of birch or linden?
Because oak and elm, when soaked and softened, become elastic and do not break, while birch and linden splinter on all sides.
All this is due to the fact that the coherence of particles in oak and birch wood differs in degree.
CHAPTER IV
crystals
If salt is stirred up in water the particles of the salt are diffused through it and become invisible, but if more and more salt is added then at last the salt ceases to dissolve, and, however much you stir it, the salt remains like a white powder at the bottom. The water had dissolved the salt to the point of saturation and could take no more. But if the water be heated it will dissolve more; and the salt which refused to melt in the cold water will dissolve away. But if still more salt be added, then not even boiling water will dissolve it. Now, if you still continue to boil the water, the water itself will evaporate in the form of steam, and the salt will be left.
So it is of everything which water dissolves: the water has a limit beyond which it ceases to dissolve substances. Everything is more readily dissolved by hot water than by cold water; but, nevertheless, when the hot water is saturated, it ceases to dissolve any more. The substance remains unchanged but the water may pass off as steam.
If powdered saltpeter is dissolved in water and then
