“Let us put a few handfuls of ashes to boil in a pot of water. After boiling a little while we will let the contents cool. The ashes settle to the bottom and the liquid at the top becomes clear. Well, we shall find this liquid emitting a peculiar odor, exactly like that which comes from the lye obtained by passing water through a barrel of ashes. We shall also find that it has an acrid, almost burning taste. This smell of lye, this acrid taste were not in the water at first; they come from the ashes, which have yielded a certain constituent to the water. “Hence we see that ashes must contain at least two substances of different kinds, of which the principal one cannot dissolve in water, but settles at the bottom as an earthy deposit, while the other, forming but a very small part of the whole, dissolves easily in water and gives it its properties, especially its odor and its acrid taste. “If we wish to obtain this latter element by itself, we can very easily do so. All that is necessary is to put the clear liquid into a pot over the fire and boil it until all the water has evaporated. There will be left a very small quantity of whitish matter resembling table salt. But despite its appearance it is not table salt by any means; far from it, as we shall quickly discover from its unbearable taste. It is known as potash, and it is what makes lye so good for cleaning linen. Furthermore, of the various components of ashes it is the one most essential to vegetation. Every tree, every shrub, every plant, even to the smallest blade of grass, contains a certain proportion of it, sometimes larger, sometimes smaller, according to the kind of plant-life, and therefore must find it in the soil in order to thrive. Let us add that in growing plants potash is not as the action of fire leaves it after the plants have been reduced to ashes. In nature it is combined with other substances which free it from that burning acridity. In the same way carbon, when combined with other elements, loses its blackness and hardness; in fact, it is no longer common coal.