_Liquoring of Soaps._--This consists of the addition of various alkaline solutions to soap to produce different qualities, and is best performed in the crutching machines, although it is in some instances carried out in the frames. In the history of soap-making a large number and variety of substances have been suggested for the purpose of accomplishing some real or supposed desirable effect when added to soap. Many of these have had only a very short existence, and others have gradually fallen out of use. Amongst the more practical additions most frequently adopted may be mentioned carbonate of soda, silicate of soda, and pearl ash (impure carbonate of potash). The carbonate of soda may be used in the form of "soda crystals," which, containing 62.9 per cent. of water, dissolves in its own water of crystallisation on heating, and is in that manner added to the hot soap. In the case of weak-bodied soap, this addition gives firmness and tends to increase the detergent qualities. The soda carbonate may also be added to soap as a solution of soda ash (58 deg. alkali) either concentrated, 62 deg. Tw. (34 deg. B.), or of various strengths from 25 deg. Tw. (16 deg. B.) upwards. This solution stiffens and hardens soap, and the addition, which must not be excessive, or efflorescence will occur, is generally made at a temperature of 140 deg. F. (60 deg. C.). Care should always be taken in the choice of solutions for liquoring. Strong soda ash solution with a firm soap will result in a brittle product, whereas the texture of a weak soap would be greatly improved by such addition. A slight addition of a weak solution of pearl ash, 4 deg.-8 deg. Tw. (2.7-5.4 deg. B.), improves the appearance of many soaps intended for household purposes. For yellow soaps, containing a low percentage of fatty acids, solutions of silicate of soda of varying strengths are generally used. It is always advisable to have a test sample made with the soap to ascertain what proportion and what strength of sodium silicate solution is best suited for the grade of soap it is desired to produce. It is important that the soap to be "silicated" should be distinctly alkaline (_i.e._, have a distinct caustic taste), or the resultant soap is liable to become like stone with age. The alkaline silicate of soda (140 deg. Tw., 59.5 deg. B.) is the quality most convenient for yellow soaps; this may be diluted to the desired gravity by boiling with water. For a reduction of 3-4 per cent. fatty acids content, a solution of 6 deg. Tw. (4 deg. B.) (boiling) is most suitable, and if the reduction desired is greater, the density of the silicate solution should be increased; for example, to effect a reduction of 20 per cent. fatty acids content, a solution of 18 deg. Tw. (12 deg. B.) (boiling) would probably be found to answer.