[CHAPTER XIX.]
DETERMINING THE REAL VALUE OR PERCENTAGE OF COMMERCIAL SODAS, CHLORIDE OF LIME, ETC.
Examination of Commercial Sodas.—Mohr's Alkalimeter.—Preparation of the Test Acid.—Sampling Alkalies.—The Assay.—Estimation of Chlorine in Bleaching Powder.—Fresenius' Method.—Gay-Lussac's Method.—The Test Liquor.—Testing the Sample.—Estimation of Alumina in Alum Cake, etc.
In a manufacture such as paper-making, which involves the consumption of enormous quantities of materials of variable quality, as soda ash, caustic soda, and bleaching powder, for example, it will be readily seen that some means should be at the command of the consumer who does not avail himself of the services of a practical chemist at his works, by which he can ascertain the actual value of the various substances he uses. An art which, up to a certain point in its progress, is mainly a chemical operation, it would undoubtedly be more safely and economically conducted when supervised by persons well acquainted with chemical principles and reactions, and less dependent upon individual judgment, than is, perhaps, too frequently the case. Under such supervision more perfect uniformity of results—a consideration of the greatest importance in a manufacture of this kind—would be ensured.
Fig. 83. Fig. 84. Fig. 85.
Examination of Commercial Sodas.—The methods of determining the percentage of real alkali in the commercial products which have received the name of Alkalimetry are fortunately of a simple character, and such as a person of ordinary intelligence and skill can readily manipulate and render thoroughly reliable by exerting the necessary care. He must, however, be provided with a few indispensable appliances, which will be described, and with these he should make several trials upon various samples until he finds that his results are uniform and his manipulation easy and reliable. He will require a chemical balance,[34] capable of weighing to the tenth of a grain; a few glass "beakers" (Fig. 83) of various sizes, capable of holding from four to eight or ten ounces of fluid; several glass stirrers; a bottle of litmus solution, made by dissolving litmus in hot water; books of litmus and turmeric papers; and several glass flasks (Fig. 84) of various sizes, capable of holding from four to eight ounces. Besides these accessories, certain measuring instruments, termed alkalimeters or burettes, are employed, of which either of the two following may be employed. These instruments are of glass, and hold up to 0 or zero exactly 1,000 grains. The scale is graduated in a hundred divisions, which are again subdivided into tenths. Bink's burette is shown in Fig. 85, and Mohr's burette in Fig. 86. The latter, being provided with a stand, enables the operator to add the test liquor—with, which the burette is charged—drop by drop, when the alkaline solution to be tested is near the point of saturation, without engaging the hands.
