. The manufacture of pulp and paper : a textbook of modern pulp and paper mill practice. further particulars, the reader is referred to the works ofCross and Bevan, Sutermeister, and Johnsen and Hovey. 69. Sulphuric Acid Test.—25 milligrams of air-dry and finelydisintegrated pulp is dissolved in 501 of cold, chemicallypure, sulphuric acid of sp. gr. in a graduated tube having aground-glass stopper. In a second tube of the same dimensions,a standard pulp is treated in identically the same manner; afterthoroughly shaking, the colors of the two solutions are compared,and sulphuric acid
. The manufacture of pulp and paper : a textbook of modern pulp and paper mill practice. further particulars, the reader is referred to the works ofCross and Bevan, Sutermeister, and Johnsen and Hovey. 69. Sulphuric Acid Test.—25 milligrams of air-dry and finelydisintegrated pulp is dissolved in 501 of cold, chemicallypure, sulphuric acid of sp. gr. in a graduated tube having aground-glass stopper. In a second tube of the same dimensions,a standard pulp is treated in identically the same manner; afterthoroughly shaking, the colors of the two solutions are compared,and sulphuric acid is added to the first pulp until the color ofthe solution matches that of the standard. The total number of 1 Klason recommends 20 §8 Tl STING OF PULP 43 of sulphuric acid required to obtain the standard color indi-cates the purity of the pulp. The test is, of course, only comparative; it does not give theactual percentage ofIignin. It is useful inmills where there is nogreat variation in qual-ity, but it is not recom-mended for comparisonof pulps from OXYCELLULOSE TEST 70. Determination ofCopper Figure, Cu. F.—This test for oxycellu-lose was developed bySchwalbe, and the resultobtained by it is calledthe copper number orcopper figure, sometimesabbreviated to Cu. test depends uponthe reduction of the cop-per in Fehlings solutionby aldehydic groups inoxycellulose. Coloringmatter and Iignin givethe same reaction. Theresults of the tests are ex-pressed as the number ofgrams of copper reducedfrom Fehlings solutionby 100 grams of bone-dry pulp. The exactstructural formulas ofthese reducing com-pounds being unknown, it is not possible to obtain any ratio between the oxycellulosecontent and the normal cellulose content. The test must be 44 REFINING AND TESTING OF PULP §8 closely controlled, since Fehlings solution decomposes spontan-eously, even while the reducing action is taking place; but thisreducing action may be considered to be constant,
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