In order to produce the oxymuriatic acid, bleach ers follow different methods to obtain a liquor which they suppose possesses the highest bleaching powers. In one point they generally agree, which is, in gi ving a superabundance of the materials employed, by which they are certain of procuring a liquor which possesses high bleaching powers. One of the most common proportions of materials employed for ma king this acid, is to take equal parts, by weight, of common salt and manganese, which are intimately mixed together. Some bleachers moisten the mix ture with water, to the consistence of a thick paste, so that the dissolved salt may incorporate more inti mately with the manganese. Au equal weight of sulphuric acid is taken as of the other materials, which is diluted with its bulk of water, and allowed to cool before being poured into the retort on the combined salt and manganese. Tho charge for the distillation thus consists of equal parts of salt, man ganese, and sulphuric acid, &lilted with an equal bulk of water.
In the above proportions of the materials, it is evi dent, that the quantity of sulphuric acid employed is more than sufficient for expelling. the murtatlr acid from the salt ; two-thirds of the former acid being enough to disengage the latter at a moderately high 3 temperature. Hence, when equal parts of salt, man ganese, and diluted sulphuric acid, are used in' the distillation of the oxymuriatic acid, the residuum ta ken from the retort is uniformly found to be super sulphate of soda combined with manganese. The quantity of manganese used is also too great, and much of this substance is wasted, no more being ne cessary than is sufficient fully to oxygenise the mu riatic acid during the distillation.
At the same time, it is proper to remark, that the proportion of manganese must be subject to variation according to its quality.
Mr Rupp of Manchester ( Trans. of the Lit. and Phil. Soc. of Manchester, vol. v.) recommends, man ganese 3 parts, common salt 8, sulphuric acid 6, water 12. The bleachers in the neighbourhood of Glasgow commonly use equal parts of salt, manganese, sulphu ric acid, and water, as mentioned above. In Ireland, the common proportions are said to be, manganese 6 parts, common salt 6, sulphuric acid 5, water 5. In France and Germany, we understand, they vary little from the following : manganese 20 parts, com mon salt 64, sulphuric acid 44, water 54.
Besides the above methods of making the oxymu riatic acid, that which was originally introduced by Mr Berthollet has again been used by several bleach ers, on account of the high price of potash. It con sists of introducing one part of oxide of manganese into the retort, on which is poured two parts of mu riatic acid, of the specific gravity of 1200, which is diluted with its bulk of water.
The reason given by those who have again resorted to the latter process for making this acid, is, that one-half of the quantityof alkali is sufficient for neu tralizing it in the receiver, because the oxymuriatic acid gas is presented in a pure state without any mix ture of sulphureous acid gas, which they suppose is always produced by a part of the sulphuric acid be ing decomposed in the retort by the impurities mixed with the oxide of manganese ; and that, in conse quence, one-half of the alkaline lixivium is sufficient, no more alkali being necessary than a sufficiency to retain the oxymuriatic acid gas in a proper state of neutralization for the purposes of bleaching. What
ever of theory may he in these inferences, it is cer tain, that bleaching liquor made in this manner pos sesses power equal, if not superior, to any in use, for rendering goods white expeditiously.
We shall now describe the preparation of the oxy muriatic acid combined with potash, as conducted in the apparatus invented by Mr Fisher. See Plate LVI. Fig. 4.
Supposing the receiver K to contain 120 gallons English nine measure, it is filled at the hole M with a solution of caustic potash of the specific gravity of 1015 ; the lead stopper is then replaced. Twenty one lbs. of common salt being intimately mixed with fourteen lbs. of the black oxide of manga nese, the mixture is moistened with water, and wrought together until it is of the consistence of moist dough. By this means, the salt, in a state of solution, unites more intimately with the manganese. The top of the retort being removed, the salt and manganese are put into it ; the cover is then replaced, and firmly screwed on its place.
Into 16 lbs. of sulphuric acid pour gradually the same weight of water, and allow the mixture to cool. One half of the diluted acid is poured, by a lead fun nel, into the retort by the hole at C, which is then closed by the lead plug to prevent the escape of the oxymuriatic acid gas which is instantly disengaged, after which a violent agitation is heard in the receiver K. The distillation is usually begun in the evening, and the workman, after seeing the operation going, properly forward, leaves it to work of itself. In the morning, the distillation having abated, the remainder of the diluted sulphuric acid is poured into the re tort, when a fresh disengagement. of the gas takes place. As soon as it is observed to slacken, a fire is put into the furnace in order to heat the boiler B, which is filled with water, into which chaff or any similar light substance is put to prevent the evapora tion of the water. By the increased heat of the wa ter, the distillation goes forward with renewed vigour ;. and the fire is continued until no more gas is dim', gaged, which is known by the bubbling noise in the receiver being no longer heard. The oxymuriatic acid combined with potash may now be drawn off by the stop.cock N from the receiver for use.