ALKALI. A name first applied by the Arabians to the carbonates of soda and potash derived from the ashes of plants, but now extended to those substances which dissolve in water,generally form Seeps With oils,'and form ing crystalline salts. The chief alkalies of importance in the arts are potash, soda, ammonia, and quinia. They have a com mon effect upon some colors—such as turning the red colors of roses, cabbages, and radishes to green, the red of litmus to purple, and the yellow of turmeric and a few other vegetable dyes to brown. Even when these three first named alkalies are united with carbonic acid, they exert the same reaction, by which they are readily distinguished from lime and magnesia. When pure they have an acrid and urin ous taste, dissolve animal matter readily, and unite with oils : they also unite with water in any proportion. A strong solu tion in water is termed a lye or ALKALIMETER. An instrument used for testing the strength of the alkalies of commerce. The operation is termed al kalimetry, the general principle of which i consists ascertaining the quantity of real alkali in a given weight of the sub stance examined, by finding how much of the latter is required to neutralize a known quantity of an acid—as sulphuric acid. The first step is to prepare a stock 1 of dilute sulphuric acid of a known strength, containing for example, 100 grains of real acid in every 1000 grain measures of liquid. A large quantity—as a gallon or more—may he prepared at once : thus, the oil of vitriol, if it be good and of the specific gravity of 1.85, con tains in every 49 grains 40 grains of ab solute acid. 'For the proportion required above—every gallon or 70,000 grams of dilute acid-7000 grains of real or abso lute acid is demanded ; this, at the com position of the acid given, is equal to 8571 grains of common oil of vitriol. All that is required, is then to weigh out 8571 grains of vitriol and dilute it with water until when cool the mixture shall measure exactly one gallon.
The " Alkalimeter" is next to be con structed out of a piece of even cylindri cal glass tube, fifteen inches long and six-tenths of an inch wide internally, closed at one end and moulded into a spout or lip at the other ; a strip of paper is pasted on the tube and suffered to dry, after which it is graduated by counter poising it in a nearly upright position in the pan of a delicate balance, and weigh ing into it successively one two, and three hundred grains of distilled water at 60° until the whole quantity of 1000 grains be reached, the level of the tube after each addition being carefully marked with a pen upon the strip of paper while the tube is held quite upright and the mark made between the to and bottom of the curve formed by the surface of the water. The smaller divisions of each
hundred parts may then be made with the compass into tenth parts. The gra duation being accurate and complete, the operator may transfer the marking to the glass by means of a file, and the paper may be removed with hot water. The numbers can be scratched with the hard end of the file. When this instrument is used with the dilute acid above, every division of the glass will correspond to one grain of real acid.
The alkali is examined thus : 50 grains of the sample are weighed, dissolved in warm water, and if needful, filtered : the alkalimeter is then filled to the top of the scale with the dilute acid, and the latter poured from it into the alkaline solution, which is tried from time to time with red litmus paper. When the solution, after being heated a few minutes, no longer affects either blue or red litmus, the measure of liquid employed is read off, and the quantity of soda or potass present in the state of carbonate or hy drate in the 50 grains of salt, is found by the rule of proportion. Suppose soda was the alkali, mid that 33 measures of acid had been used then by taking their atomic proportions in which the acid and soda unite, it would stand thus : as Sulph. acid 4D : soda 31.9 : • 33 : 25.6 in 50 grains. The sample therefore con tains 51.2 per cent. of available alkali. The quantity of alkali in a carbonated form may be known •bv weighing the body before and after tie expulsion of carbonic acid ; from the loss may be cal culated the per ventage of alkali. By the use of Fresenius's apparatus for this pur pose, the precision attained leaves no thing to be desired.