In the above process, the sulphuric acid having a. greater affinity for the soda contained in the common salt than that which the muriatic acid has, the latter is disengaged from the soda, and, acting on the man ganese, it deprives it of its oxygen, which now exist ing in the state of oxymuriatic acid gas, by its ex pansive force is impelled forward through the tubes G and I into the receiver K, where it is absorbed by the caustic alkaline solution.
V. No farther improvements seem to have taken place in the combination of this acid with any other substance than the alkalis until the year 1798, when Mr Charles Tennant of Glasgow, by a well conduct ed series of experiments, spewed, that it was capable of being united with what are called the alkaline earths, such as barytes, strontites, and lime. Lime being most readily procured, after a number of trials he found, that, by mechanical agitation, and in con sequence of the suspension of the finer particles of the lime in water, it readily united with the oxymuri atic acid gas, and was thereby completely dissolved. When, therefore, a sufficient quantity of finely pul verised quicklime is put into the receiver K in place of potash, and mechanically agitated during the dis tillation of the oxymuriatic acid, it will be found that it is entirely dissolved, and forms a pure and transpa rent solution of oxymuriate of lime, possessing the same power of retaining the gas as the alkalis do.
Mr Tennant has since carried this improvement to a greater degree of perfection, by combining the oxy muriatic acid with quicklime in the dry way, and thus rendering it portable to any distance at a small expence. For this further improvement he justly re, ceived another patent, which secures him the exclu sive right of this valuable manufacture. This disco very is of great importance, as, by means of so com mon and cheap a substance as lime, great savings are made by the bleacher in the expence of alkali ; and this improvement may not improperly be called a new era in the history of bleaching.
For use, the concrete oxymuriate of lime is diffused in water by agitation ; the insoluble matter contained in the lime is allowed to subside until the liquor is transparent. When drawn off for use, it is further di luted with water before the goods are immersed in it, in order to be whitened.
VI. The oxide of manganese, when of a good qua lity, is of a black shining colour ; when combined with oxygen at a maximum, it contains 4.4 parts of the metal with 66 parts of oxygen ; but as taken from the mines which contain it, it is never found so pure. The principal defect of manganese arises from its be ing united with chalk, or ores of iron ; and when any of these are mixed in quantity with it, its effect is proportionably weakened in making bleaching liquor.
The presence of carbonate of lime may he discovered in manganese, by pouring on a portion of this sub stance nitric acid diluted with eight or ten parts of water. If the manganese be good, no effervescence will ensue, nor will the acid dissolve any thing ; but if carbonate of lime be present, it will be taken up by the acid. To the solution add a sufficient quan tity of carbonate of potash to precipitate the lime. Its weight will show how much chalk the manganese under examination contained.
The adulteration of manganese when it is mixed •with the ores of iron is less easily discovered. But if the iron be in such a state of oxidation as to be soluble in muriatic acid, the following process may discover it : Dissolve a portion of the manganese in strong muriatic. acid, with the assistance of heat ; di lute the solution largely with rain-water, and add a solution of crystallized carbonate of potash. The manganese will remain suspended by the excess of carbonic acid, but the iron will be precipitated in the state of a coloured oxide, on mixing the two so lutions. From an observation of Klaproth's, (Es says, i. p. 572.) it appears that oxides of iron are se parable by nitrous acid, with the addition of sugar, which takes up the manganese only.
VII. Sulphuric acid, or oil of vitriol, as it is com monly called, when pure, is a transparent, colourless fluid, slightly viscid, and without smell. The speci fic gravity of the sulphuric acid of commerce is gene rally 1850, or almost twice the weight of distilled water. The manufacture of it is now carried on to such extent in Great Britain, that any further de scription of a substance so well known is unnecessa ry. The only substances with which it is ever adul terated are lead, and supersulphate of potash. A small portion of lead is taken tip during its formation, in chambers of that metal, and its subsequent concen tration in boilers. On this account, a white precipi often found in the bottom of the bottles con taining it, which is sulphate of lead. After the com bustion of the sulphur and nitre in the manufacture of sulphuric acid, supersuiphate of potash is left as a residuum, by the affinity of the potash contained in the nitre with the sulphuric acid. Sonic manufactu rers add a strong solution of this salt to the water which is put into the lead chambers where the sul phuric acid is formed. Now, in proportion to the quantity of potash contained in this solution, in so far is the specific gravity increased, and, in conse quence, the sulphuric acid is rendered ineffectual for answering the purposes of bleaching.
This adulteration is carried so far as frequently to leave only four-fifths of pure acid. Hence it ought to be the bleacher's study to purchase what contains only pure sulphuric acid.