Composition of wood ash
Analysis of the ash reveals the existence of mineral or metallic substances drawn from the soil by the plant.
In the form of combinations, these substances appear only in small quantities. These are mainly:
- sulfur, phosphorus, chlorine, silicon, potassium, calcium, magnesium, iron, sodium.
Others are found in wood only exceptionally such as aluminum, zinc, boron ...
1 - We note first of all a variation of mineral matters with the species. Thus we find more chlorine in conifers than in hardwoods (7 times more in spruce than in oak).
We will find twice as much phosphoric acid in aspen as in oak, and twice as much magnesia in elm as in Scots pine.
Comparisons obviously bear on wood grown in the same geographical conditions.
We can consider that the inorganic elements that constitute the ashes are predominantly basic ph with 48% lime, 13% potash and soda and 9% oxides such as: magnesia, iron oxide, manganese oxide.
Acid constituents: phosphoric acid, silicic acid, sulfuric acid are less present in the ash.
Ash can therefore be used to increase the pH of too acidic soil.
2 - The nature of the soil has a considerable influence on the chemical composition of the ashes. The tree draws from the ground the elements which suit it in a proportion which is all the greater the more abundant there is. Thus in a silico-limestone ground the chestnut will absorb 15% less limestone than if it is planted in a chalky ground.
3 - The nature and quantity of the mineral matter forming the ashes also vary with the various parts of the tree. The bark contains more than the wood, the branches more than the trunk and the trunk more than the roots. Silica and lime are more abundant in bark than in wood, while potash dominates in wood.
4 - There was also a variation according to the slaughter season. If we cut in summer, we find a higher proportion of potash and phosphoric acid. These elements favoring certain fermentation organisms, Conservation of such wood will be worse.
5 - Where are the mineral elements preferably located? In some cases these elements normally permeate the cell walls with their solutions.
Sometimes they also form crystals visible under a microscope, in the cell cavity. These crystals of lime oxalate, of silica lime carbonate sometimes even appear to the naked eye.
6 - The properties of woody matter can be quite strongly influenced by the presence of mineral matter. Phosphoric acid and potash, in the presence of water, and at the right temperature, are first-rate foods for molds.
Some old people can still remember the time when laundry was done with wood ashes, thus using the natural potash they contain and, in the Middle Ages, the soda needed for the manufacture of glass was introduced by means of beech ash or certain herbs particularly rich in this product.