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Home > upon the lye and forms...
Previous Next The best candle and soap tips online! upon the lye and forms upon it a cover, which completely shuts out the carbonic acid. For this no special vessels are needed, lind it may be placed in tanks or in the so called pits;—as thereby the paraffine is in no wise changed, we can always make renewed use of it. In testing the strength of lyes, formerly an egg was used— and in many instances this is yet done—for the approximate estimation, whether a lye possessed the necessary strength for the paste or preliminary operation, the lye had to attain such a density that a hen's egg would float upon it. At a more progressive period hydrometers were used for this purpose and are yet frequently applied. There is no doubt that the latter instrument would show with sufficient accuracy the quantity of alkali dissolved in the water if for the production of lyes pure carbonate alkalies were used. But as such is not the case, and the potash as well as the soda contains larger or smaller quantities of foreign salts, soluble in water, this method of testing, based upon the specific gravity, can never furnish positive results, and there may be lyes which although they prove themselves high on the scale of an hydrometer, yet may be proportionately weak in caustic alkali. On the other hand, the alkalimetric test offers the most perfect security, and the modus operandi is similar, as we have already related, in the case of testing potash and soda. The main thing is, that a correct testing acid be provided, and it would be best to prepare it for the purpose,and, moreover, such an one, as may be applied as well for potash as for soda-lyes. We have, heretofore, for a testing acid, recommended nitric acid ; but its treatment offers to those who are not chemists certain difficulties, and for this reason we would recommend to soap manufacturers crystallized oxalic acid. It has in its crystallized state always the same composition, and can, as it is dry, always be accurately weighed. 63 grammes (2.2 ozs.) of purified oxalic acid (in case of necessity the commercial oxalic acid may be used) are dissolved into 1 litre of water. It corresponds to 47.11 grammes (1.65 ozs.) caustic potash, and 31 grammes (1.09 ozs.) caustic soda, each cubic 256 TECHNICAL TREATISE ON SOAP AND CANDLES. THE FABRICATION OF SOAPS. 257 centimetre, therefore, 0.047 grammes (0.725 grains) potash and 0.031 grammes (0.478 grains) soda. If a lye is to be estimated, take into a beaker glass, or still better, in a porcelain cup 10 cubic centimetres (2.70 flui-drachms) thereof, then add about 10 drops of litmus tincture, and then by means of a -^ cubic centimetre (0.027 flui-drachm) graduated pipette,add the oxalic acid solution until the blue color of the liquid has changed into an onion-red. Supposing now we had by this transaction used upon a potash lye 10 cubic centimetres (2.70 fluidrachms) oxalic acid, then there are in the 10 cubic centimetres of the applied lye 0.47 grammes (7.25 grains) potash, or, if soda lye had been estimated, 0.31 grammes (4.78 grains) soda contained in the lye; the one lye contains, therefore,4.71 grammes (72.7 grains) or per cent, potash, the other 3.10 grammes (47.83 grains) per cent. soda. To show at once that in such like tests it is not important to obtain the highest degree of accuracy, that is to have absolutely pure oxalic acid, we will suppose the applied oxalic acid had contained but 95 per cent, pure oxalic acid, an amount of impurity hardly ever found. In fact there would in such a case as is shown above if 10 cubic centimetres (2.70 fluidrachms) oxalic acid had been used, not 4.711 grammes (72.69 grains) potash, or 3.10 grammes (47.83 grains) soda, have been the proper contents of the lyes, but only 4.711: 0.95 = 4.4(67.9 grains) potash, respectively 2.945 percent, soda, so that the difference in both cases amounts to about J per cent. But another test of the lye can be made in this manner, by placing with a pipette 4.71 cubic centimetres (1.27 fluidrachms) potash-lye, or of a soda lye 3.1 cubic centimetres (0.84 fluidrachm) in a cup, bluing it with litmus tincture, and then by means of normal oxalic acid solution titrate until an onion-red color appears. In this case the cubic centimetre of acid used, multiplied by 10, gives the content of the caustic alkalies without further calculation. But it is always best for such tests to apply purified oxalic acid, for which purpose the crude oxalic acid is dissolved in double its weight of heated distilled water and the solution filtered, when after cooling oft", the acid will crystallize in a sufficiently pure condition. It is then brought upon a filter, and dried in the open air upon tissue paper without warming it, until a crystalline powder is formed. Whenever the application of oxalic acid seems too troublesome, the test acid may be sulphuric acid, of which 55 grammes (1.93 ozs.) are weighed off and diluted with water to 1000 cubic centimetres, one litre (2.1 pints). To have this acid mixture correct, dissolve 5.3 grammes (81.78 grains) fresh heated pure carbonate of soda in 100 cubic centimetres (3.38 fluid ozs.) liquid ; of this transfer 10 cubic centimetres (2.70 fluidrachms) by the pipette into a porcelain cup, adding tincture of litmus, and also from a graduated pipette so much sulphuric acid until the liquid has assumed an onion-red color, and by warming again does not again turn blue. If the sulphuric acid had been correctly mixed, then 10 cubic centimetres of it would have been accurately used; to occasion that change of color, generally, however, there will be— according to the above proportions between water and sulphuric acid—less than 10 cubic centimetres used of the testing acid, and the deficiency must be made up of pure water. Supposing, instead of 10 cubic centimetres (2.70 fluidrachms) but 9 cubic centimetres (2.43 fluidrachms) had been applied, then to the litre of testing acid, 99 cubic centimetres (3.34 fluid ozs.) water must be added. We have already explained, that in order to determine the strength of a lye with some degree of accuracy, we cannot depend upon a hydrometer, but will prove by an example what differences may ensue under certain conditions. Thus a lye containing 14.52 per cent, of caustic soda of the specific gravity of 1.255 = 29.5° B., and according to this should have contained 16.635 per cent, of soda. If the requisite quantity of the lye for decomposing the neutral fat had been determined by means of a hydrometer in this case, we should have applied 2 per cent, of soda less than was necessary for a complete saponification. The soda from which that lye had been prepared contained 72 per cent, anhydrous carbonate of soda, hence we have an inferior article. Under certain conditions a hydrometer may, of course, be used for determining the 17 258 Previous Next
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