Man's Conquest of Substances
To any acid solution add gradually a small quantity of a base, and test the mixture from time to time with blue litmus paper; at first the paper will turn red quickly, but as more and more of the base is added to the solution, it has less and less effect on the blue litmus paper, and finally a point is reached when a fresh strip of blue paper will not be affected. Such a result indicates infallibly the absence of any acid qualities in the solution. If now red litmus paper is tested in the same solution, its color also will remain unchanged; such a result indicates infallibly the absence of any basic quality. The solution has the characteristic property of neither acid nor base and is said to be neutral.
If to the neutral solution an extra portion of base is added, so that there is an excess of base over acid, the neutralization is overbalanced and the red paper turns blue. If to the neutral solution an extra portion of acid is added, so that there is an excess of acid over base, the neutralization is overbalanced in the opposite direction, and the solution acquires acid characteristics.
Most acids and bases will eat and corrode and discolor, while neutral substances will not; it is for this reason that soap, a slightly alkaline substance, is the safest cleansing agent for laundry, bath, and general work. Good soaps, being carefully made, are so nearly neutral that they will not fade the color out of clothing; the cheap soaps are less carefully prepared and are apt to have a strong excess of the base ingredient; such soaps are not safe for delicate work.