Potash Manufacture.

Daily Southern Cross, Volume V, Issue 259, 21 December 1849, Page 4

Potash Manufacture.

Paper read by Sis Excellency Sir Wm. Denison at the Meeting of the Royal So ciety, Hobart Town, on tlie 15th November, 1849. The following sketch of tho hest mode of proceeding may perhaps be of service to those who are inclined to make the experiment, with the view of reducing the cost of clearing ground, and preparing it for cultivation. The timber must be piled in large heaps, aud burned in still weather if possible ; the ashes, when the heaps are consumed, must be sifted j the larger parts, or charooal, must be returned to the fire, and burned to ashes. These, as soon as the sifting is completed, must be stowed away under cover, until it is desirable to commence the lixiviation. For this a certain number of casks must be prepared, by having a falso bottom placed at a few inches above the real bottom. Tho false bottom may either be formed of a plank perforated with holes, or an open framework ; in either case it must be covered either with a double thickness of blanket or five or six inches of clean straw. A cock will be inserted below the false bottom in each cask, These casks will be ranged alongside of each other, and a gutter will be placed under the cocks, so that the liquor, after having been filtered in these casks, may pass off to a reservoir, from which it will either be pumped or ladled into the boilers for evaporation, or be returned to the same or a fresh set of casks, to be more strongly impregnated with the soluble salts of the ashes. The casks being thus arranged, a quantity of ashes is placed in each, and an equivalent bulk of water is poured upon the top of these, the quantity of ash being so reguJafced as to nearly fill the cask when the water has been poured upon it. The water is allowed to remain undisturbed for about 24 hours, when the casks are opened, and the whole is discharged into the reservoir. Another charge of water is then poured upon the ash ; and this, after being allowed to remain contact with the ash for about three or four hours, is drawn ofi into the same reservoir. In some instances it may be as well to commence at one to evaporate these two solutious, in order to clear the reservoir for reception of the liquor of two or more washings of the same ash ; but in others it may bo as well to have a second reservoir for the water of the two last washings, which will never be rich enough in potash to make it worth while to evaporate it. After having been thus washed with four times its bulk of water, the ash, tho' still containing some potash, may be emptied out of the cask, and thrown away, and a second obarge introduced. X the first lixiviafcion should prove weak, it may be used instead of water for the first washing of the second quantity of ash ; but, generally speaking, it will be as well to evaporate the product of the two first -washings of the quantity of ash, and to use the third and fourth washings instead of water for the first and second washings of the second charge of ashes. The process will then go on regularly : the two last washings of each charge being used as the two first of the succeeding charge, and the two first washings of each being removed to the boilers for the purpose of being evaporated. The arrangements for evaporation are simple enough. A couple of iron pots, or a greater number, in proportion to the quantity of ashes.. to be reduced, will be all the apparatus required. The solution before described will be pumped or ladled into these pots ; and a fire being kept up, the water will gradually pass away in steam. It would be as well to keep filling the boiler with fresh solution as fast as the water was evaporated, so that the contents would become more and more concentrated; and at last, when the boiler was nearly full of matter of the consistence of honey, no more of the solution should be added ; but the fire might be forced, until the whole ef the water being drawn off, the potash itself would enter into fusion, which it would do at a low red heat. During this latter

part of the process, care must be taken to keep stirring the potash with an iron rod ; and when the whole has entered into fusion the fire may be withdrawn from under the boiler, and the mass allowed to cool ; the stirring being still continued in order to granulate the potash, and to secure the escape of all carbonaceous matter, which may injure the marketable quality of the potash by darkening the colour. With reference, too, in the same risk, I may state that the solution should, after being withdrawn from the casks into the reservoir, bo allowed to settle for 24 hours at least, in order to deposit any sodiment, or colouring matter which it may contain ; and care should be taken in withdrawing the solution from the reservoir for the purpose of evaporating it, that the sediment should not be disturbed, In some cases, where the solution appears to be very dark coloured, it may be as well, after evaporating the water till the solution is almost ready to enter into crystallisation, to withdraw it from the boiler into some flat troughs or pans, and then to allow it to crystallise, If these crystals be then dissolved in a quantity of water only just sufficient for the purpose, and tho solution be allowed to remain undisturbed for 24 hours, it is probable that a large portion of the extraneous matter will be separated and deposited ; the liquor being then drawn off with a syphon, and evaporated, the product will be a clean well-coloured potash, When the potash has been fused as before directed, and gradually cooled down, it will be removed from the boiler and packed in casks, well hooped and secured, | and it is then fit for exportation. I will now give a few details which may serve as elements upon which some idea may be formed of the amount of the return from any given quantity of timber, or any given area of ground. — From the experiments made by Captain Stanley, it appeared that the amount of ash from the wood and bark alone varied, according to the description of timber, from 10 to 25 lbs, per ton. In this case the timber was burnt in a reverbatory furnace, with a strong draught, and it is possible that a portion of the ash was carried up the chimney. In some experiments made at one of the convict stations, the proportion of ash was much larger in the same description of wood ; but in this case there is some reason to think that some extraneous matter might have been included in and weighed with the ash. The proportion of 1 lb. of potash to 10 lbs. of ash is that given in the best works which treat on the ( subject, and it is corroborated to a certain extent by the experiments made here. What then, in the first place, may be as sumed to be the quantity of timber, including branches and leaves, in a heavily wooded district of this colony ? Upon a rough computation I should say from 600 to 1200 tons. If, then, the quantity of ash be taken on an average at 10 lbs. per ton of weod, the weight of ash will be from 6,000 to 12,000 lbs., and the quantity of potash from 600 to 1,200 lbs. per acre. The value of the potash in the English market is now from £38 to £40 per ton, deducting £8 for freight and charges, value of casks, &c. The value of the potash on the ground would be 30s. por cwt M or 265. 9d. per 100 lbs., and the return per acre would amount to from £8 to £16, — an ample return for the cost of manufacture, when it is considered that land which would otherwise be altogether unavailable will be laid open, and be ready for the plough. lam in hopes that I may be able to give at some future period some more positive statements than the above ; but they are sufficiently valuable to warrant their adoption. j