63

C—3A

Na 2 S Solution. A 50 cc sample of liquor is pipetted into a 500 cc volumetric flask, 50 cc of 10-per-cent. BaCl 2 solution added, the mixture made up to 500 cc, thoroughly shaken, and allowed to settle. A 10 cc. portion is added to a slight excess of 0-1N iodine previously acidified with 10 cc of concentrated acetic acid. The excess iodine is then titrated with 0-1N sodium-thiosulphate solution, using starch as an indicator. A = cc of 0-1N iodine solution ; B = cc. of 0-1N thiosulphate solution. (A —B) X 3-9 = Na 2 S in grammes per litre. Black Liquor : Ratio of Combined to Total Alkali. Free Alkali. A 100 cc sample of black liquor is pipetted into a 1,000 cc volumetric flask, 100 cc of 10-per-cent. BaCl 2 solution added, made up to 1,000 cc, thoroughly shaken, and allowed to settle. A 100 cc. portion of the clear solution is titrated with 0-1N HCI to phenolphthalein end point. Total Alkali. A 100 cc sample of black liquor is pipetted into a Duriron dish, evaporated to dryness, and ashed. The ash is dissolved with distilled water and made up to 1,000 cc. in a volumetric flask. A 100 cc. portion is titrated with 0-1N HCI to methyl-orange end point. x= cc 0-1N acid for free alkali; y= cc 0-1N acid for total alkali. f 100 — 100 -1 = per cent, ratio of combined to total alkali. APPENDIX IX. —METHODS OF ANALYSIS OF COOKING-LIQUORS FOR SEMI-KRAFT PROCESS. NaOH and Na 2 S Solution. A 50 cc sample of liquor is pipetted into a 500 cc volumetric flask, made up to the mark with distilled water, and thoroughly agitated. 50 cc of 10-per-cent. Ba,Cl 2 solution is added to precipitate carbonates. Allow to settle. Pipette off alO cc sample of the clear liquor and add it to an excess of 0-1N iodine solution, previously acidified with acetic acid. Enough glacial acetic should be used to neutralize all the alkali and render the solution acid. The liquor containing the Na 2 S must be added to the 0-1N iodine, and not vice versa, or low results will be obtained. Titrate the excess iodine with 0-1N thiosulphate solution, using starch as an indicator. A new 10 cc sample is titrated with 0-1N acid to methyl orange. Calculations :— Let cc 0-1N iodine = A ; let cc 0-1N thiosulphate = B ; let cc 0-1N acid = C. (A -B) x 3-9 = Na 2 S in g.p.l. {C - (A - B) j x 4-0 = NaOH in g.p.l. For analysis of black liquor see procedure under soda and kraft process. APPENDIX X.—METHODS OF ANALYSIS OF COOKING-LTQUOES FOR SEMI-CHEMICAL PROCESS. Semi-chemical Process. Na s S0 3 and NaHCO., Solution. A 2-0 cc sample is titrated, with 0-1N iodine, using starch as an indicator. An air-condenser is attached to the Erlenmeyer flask and the solution is boiled gently until all C0 2 is expelled. Each cubic centimetre of 0-1N iodine forms 1 cc. of 0-1N acid, according to the equation — Na 2 S0 3 +21 + H 2 O = Na 2 S0 4 + 2HI. The acid thus liberated reacts with the NaHCO.,. Care must be taken that sufficient 0-1N acid is present, however, to decompose all of the NaHC0 3 . If the original liquor is low in sulphite, sufficient 0-1N acid should be a.dded by means of a burette before the boiling. After all the C0 2 is expelled the flask is cooled under the water-tap. An excess of 0-1N NaOH solution, which contains a small amount of Ba,Cl 2 , is added by either a burette or pipette. The excess NaOH is then titrated with 0-1N acid, using phenophthalein as indicator. The NaHC0 3 is calculated as Na 2 C0 3 . Calculations :— Let cc 0-1N iodine = A ; let cc 0-1N acid = B ; let cc 0-1N NaOH = C. A x 3-15 = Na 2 S0 3 in g.p.l. |(A +B) - CJ= X 2-65 = Na 2 C0 3 in g.p.l.