587. To Find the Percentage of Carbonated Alkali in a Caustic Soda or Pot-ash

587.    To Find the Percentage of Carbonated Alkali in a Caustic Soda or Pot-ash. Dissolve 100 grains of the sample in 4 ounces water in a flask ; next weigh out 100 grains finely powdered crystals of oxalic acid ; add small portions of this acid at a time to the alkali in the flask, stirring thoroughly with a glass rod, and apply heat; continue to add the acid until the hot mixture tinges litmus paper slightly red; the saturation is then complete, and the acid has neutralized or combined with all the alkali, both carbonate and caustic. "Weigh the oxalic acid which remains ; and, by deducting from 100, we know how much we have used. Now every 7.87 grains oxalic acid that have been used, have neutralized 5 grains soda or 7 grains potash, according as the sample consists of caustic soda or caustic potash; hence we find the total number of grains of alkali in the 100 grains under test. By the previous method we can find the percentage of caustic alkali in 100 grains of the sample; deducting the grains of this latter from the weight of the whole alkali eliminated by the oxalic acid, the balance or remainder will be the percentage of carbonated alkali.

By these three steps we get the percentage of water, the percentage of caustic alkali, and the percentage of carbonated alkali; these added together and deducted from 100 give the percentage of foreign matter or impurity in the matter tested. (See Alkalimetry.)

588. To Make Soap-makers' Concentrated Caustic Lye

588.    To Make Soap-makers' Concentrated Caustic Lye. Boil 85 gallons water in a kettle capable of holding 150 gallons; stir in, a little at a time, 100 pounds powdered soda (or potash, if for potash lye), until it is all dissolved; then mix in gradually, by stirring, 48 pounds freshly slacked lime of a creamy consistency; the boiling must not be allowed to slacken during the whole process, until complete causticity is obtained, which may be ascertained by taking a little in a test glass, and, when cool, adding to it a few drops of nitric acid; if this causes effervescence, the causticity is imperfect and the boiling must be continued until a test with nitric acid causes no effervescence. When this is the case, the contents of the kettle should be allowed to cool and settle for about 12 hours. The clear liquor can then be drawn off into a vat lined with lead - a syphon may be used for this purpose with advantage. The lye can be made to any desired strength by evaporation.

589. To Make Concentrated Caustic Soda Lye - Kurten's Method

589.    To Make Concentrated Caustic Soda Lye - Kurten's Method. The lye fit for toilet soap must be either made from the purest German soda at 95 degrees of strength, or (which is better for the purpose) from crystallized soda. English soda of 80 to 83 degrees, such as is generally found in commerce, is not to be used, as it produces a bad article.

When the lye for finer soap is to he made, 100 pounds lime are added to 100 pounds German soda at 95 per cent., whereas 45 pounds lime to 100 pounds crystallized soda is the general proportion.

The soda is dissolved in the boiler with water, or with a weak lye remaining from a former operation at 20 degrees of strength, and afterwards added to the lime slacked to a state like broth. This mixture must boil 2 hours and be left to deposit.

The next day, the lye, which probably may be at 12 degrees (Baum'e) must be taken out, and the boiler filled afresh. The lye drawn from the lime and at 8 degrees, is poured in with it to evaporate. By this method a lye is produced at a medium of 9 or 10 degrees, but it must be evaporated till, according to areometer, it shows 34 degrees. After the cooling it will weigh 36 pounds. This evaporation of the lye is to increase its causticity, and to cause all the dirt contained in it to precipitate to the bottom, which can be done in a day if it is sufficiently strong.

The clear lye is then drawn off from the dirty deposit, and put either into vitriol bottles or into an iron vessel well covered. If vitriol bottles are used, they must be filled with water in which some lime has been dissolved, to take away any acid remaining in the bottle, which would, if this precaution be not taken, absorb much of the causticity of the lye; and this must be done several days before using the bottles. The dirt and deposit from the salt remaining at the bottom after the boiling, can be added to the lime in the weak lyes.

We have not made the experiment of using the lye stronger than 11 degrees before evaporation, as we have learned from France that it must not be stronger than 11 degrees. Yet, after mature experience, it appears to us now that a lye can be obtained quite as good by adding more soda and lime to the lye, and thus increasing the strength to 18 or 20 degrees, by which the evaporation is spared. In this case more vessels are wanted, which must not be of wood, but of iron, because the wood will color the lye, which must be especially avoided for fine soap, for the only means of obtaining a perfect soap, free from defect, is to use none except the finest and whitest lye, and oil or grease of the greatest purity.