138 METHODS OF ANALYSIS [Chap. 



wash with 95% alcohol, dry in a water oven, and ignite in a muffle or over a Bun- 

 sen burner, applying the heat gradually at first, and avoiding a reducing flame. 

 Cool and weigh. Subtract the weight of lead sulphate so found from the weight of 

 lead sulphate found in the blank, 64, and multiply by the factor 27.325. The use 

 of this factor gives the lead number directly without the various calculations other- 

 wise required. * 

 MALIC-ACID VALUE. 



66 Cowles Melhod.^^ — Tentative. 



Weigh 6.7 grams of the sample into a 200 cc. beaker, add 5 cc. of water, then 2 

 cc. of a 10% calcium acetate solution and stir. Add gradually, and with constant 

 stirring, 100 cc. of 95% alcohol, and agitate the solution until the precipitate set- 

 tles, or let stand, until the supernatant liquid is clear. Filter off the precipitate 

 and wash with 75 cc. of 85% alcohol. Dry the filter paper and ignite in a platinum 

 dish. Add 10 cc. of N/10 hydrochloric acid and warm gently until all the lime 

 dissolves. Cool and titrate back with N/10 sodium hydroxid, using methyl orange 

 as an indicator. The difference in cc. divided by 10 represents the malic acid value 

 of the sample. Previous to use the reagents should be tested by a blank determina- 

 tion and any necessary corrections applied. 



67 METALS.— TENTATIVE. 

 Proceed as directed under XII. 



SUGAR HOUSE PRODUCTS. 



SUCROSE IN BEETS. 



68 Alcohol Extraction Method {Herzfeld Modification^^). — Tentative. 



Weigh 26 grams of the beet pulp and transfer to a 100 cc. flask with about 50 cc. 

 of 90% alcohol and 3-5 cc. of basic lead acetate solution. Connect a reflux condenser 

 to the flask and place on a boiling water bath for 10-15 minutes. Then pour the 

 whole into a Soxhlet extractor, washing out the flask with fresh portions of 90% 

 alcohol. Connect the same 100 cc. flask to the extractor, and fit the latter with 

 a return condenser. Add 90% alcohol until the siphon is started and the flask is 

 about three fourths full. Place the flask in a covered water bath kept at a heat 

 that will allow the alcohol to boil freely. Continue the extraction for .1-4 hours, 

 or until a test of the alcohol in the extractor gives no color withalpha-naphthol 

 solution when tested as follows: Introduce into a test tube a few drops of the alco- 

 hol coming from the extractor, add 4 or 5 drops of a 20% alcoholic alpha-naphthol 

 solution and 2 cc. of water. Shake well, tip the tube, and allow 2-5 cc. of colorless 

 concentrated sulphuric acid to flow down the side of the tube; then hold the tube 

 upright and, if sucrose is present, a color varying from a faint to a deep violet will 

 be noted at the junction of the two liquids. On shaking, the whole solution becomes 

 a blue violet color. This test is suitable for this work, but it must be remembered 

 that other substances besides sucrose give this color reaction. 



Remove the flask, transfer to a 100 cc. graduated flask, cool to the standard 

 temperature, dilute to the mark with 90% alcohol, shake and filter, keeping the 

 funnel covered with a watch glass. Polarize in a 200 mm. tube. 



Avoid evaporation and changes of temperature and also use a minimum amount 

 of basic acetate for clarification, 3 cc. rather than 5 cc. By digesting the beet 

 pulp with the alcohol before extraction, the time of extraction is gieUly shortened 

 the pulp becomes thoroughly impregnated with the alcohol, and all the air is re- 

 moved, resulting in a good extraction of the whole material. If the pulp is fine 



