WOOD-ASH AND CARBONATE OF POTASH. 187 



V. POTASSIUM, POTASH, CARBONATE, SULPHATE, OXALATE, TARTRATE, 



CITRATE, AND SULPHATE OF POTASH, AND CHLORIDE OF POTASSIUM. 



1°. Carbonate of Potash. — In countries where non-resinous trees 

 abound, it is usual to burn the wood which cannot otherwise be employ- 

 ed — as in the clearings in Canada and the United States — foF the pur- 

 pose of collecting the ash which remains. This ash is washed with 

 water and the washings boiled to dryness in iron pots. In this state it 

 forms the pot-ash of commerce. When (his potash is again dissolved 

 in water, and the clear liquid decanted and boiled, the^earZ-ash of the 

 shops is obtained. 



This pearl-ash is an impure form of the carbonate of potash of chem- 

 ists. It readily dissolves in water, has a peculiar taste — distinguished 

 as an alkaline taste — and dissolves in vinegar or in diluted sulphuric or 

 muriatic acid, with much effervescence. The gas given off during this 

 effervescence (or boiling up) is carbonic acid, the same which, as was 

 shown in a previous lecture, is obtained when a diluted acid is poured 

 upon chalk or common limestone. 



This carbonate of potash has been long known to exercise a powerful 

 influence over the growth of plants. 



The use of wood-ash as a fertilizer both of pasture and of arable land, 

 goes back to the most remote antiquity ; and though the crude wood-ash 

 contains other substances also, yet much of its immediate and most ap- 

 parent effect is due to the carbonate of j)otash it contains. 



From what has already been stated, at the commencement of the 

 present lecture, in regard to the presence of potash in the parts and 

 juices of nearly all plants, you will already in some measure under- 

 stand why the carbonate of potash should be useful to vegetation, and— 

 since this alkali (potash) is present in greater quantity in some than in 

 others — why it should appear to be more especially favourable to the 

 growth of one kind of plant than of another. 



In this vsray, it is explained why moss and coarse grasses are extirpa- 

 ted from meadows by a sprinkling of wood ashes — and why red clover, 

 lucerne, esparsette, beans, peas, flax, and potatoes, &c., are greatly 

 promoted in their growth by a similar treatment. This substance, how- 

 ever, has other functions to perform in reference to vegetation, besides 

 that of simply supplying the crop with the potash it requires ; these func- 

 tions I shall explain more particularly hereafter, when you will perhaps 

 be better prepared for understanding the details into which it will be ne- 

 cessary to enter. 



2°. Potash. — When 12 parts of carbonate of potash are dissolved in 

 water, and boiled with half their weight of newly-slaked quick-lime, 

 they are gradually deprived of their carbonic acid, and converted into 

 pure potash, — or as it is often called, from its effect on animal and ve- 

 getable substances, caustic j^olash. 



The caustic liquid thus obtained decomposes or dissolves most animal 

 and vegetable substances, whether living or dead. When applied to 

 the skin, unless it be in a very diluted state, it destroys it, and produces 

 a painful sore. Potash does not occur in nature in this caustic or un- 

 combined state, and is not known, therefore, to exercise any direct in- 

 fluence upon natural vegetation. 



When wood-ashes and quick-lime are mixed together in artificial 



