256 METHODS OF ANALYSIS [Chap. 



preferably in a 200 mm. tube, correcting for dilution. If basic lead acetate gives 

 only a turbidity, add to the sample, already treated with basic lead acetate, 10 cc. 

 of alumina cream [VIII, 13 (b)], shake, let stand 30 minutes, filter and polarize, 

 correcting for dilution. In the case of malt vinegar, treat 100 cc. of the sample with 

 6 cc. of 10% phosphotungstic acid solution and filter. To 50 cc. of the filtrate add 

 5 cc. of the basic lead acetate solution, filter and polarize, correcting the reading 

 obtained for dilution. 



1 3 ASH.-TENTATIVE. 



(a) Measure 25 cc. of the vinegar into a tared platinum dish, evaporate to dry- 

 ness on the steam bath and proceed as directed under VIII, 4. 



(b) Evaporate 25 cc. of the sample to dryness as directed under (a), heat in a 

 mufiJe at low heat to expel inflammable gases, treat the charred portion with a few 

 cc. of water, and evaporate to dryness on a water bath; replace in the muffle at low 

 redness for 15 minutes, and continue the alternate evaporation and heating until 

 a white or gray ash is obtained, at no time exceeding a dull red heat; cool in a 

 de.siccator and weigh. 



Useful information may often be obtained by noting the odor given off by the 

 solids during charring. 



14 SOLUBLE AND INSOLUBLE ASH.— TENTATIVE. 

 Treat the ash, obtained in 13, as directed under IX, 17. 



1 5 ALKALINITY OF THE SOLUBLE ASH.— TENTATIVE. 



Proceed as directed under IX, 18, expressing the result as the number of cc. 

 of N/10 hydrochloric acid required to neutralize the soluble ash from 100 cc. of the 

 vinegar. 



1 3 SOLUBLE AND INSOLUBLE PHOSPHORIC ACID.— TENTATIVE. 



Determine phosphoric acid in the water-soluble and water-insoluble portions of 

 the ash as directed under I, 9, dissolving the water-insoluble portion in about 

 50 cc. of boiling nitric acid (1 to 9). Express the result as mg. of phosphorus 

 pentoxid (P2O6) in 100 cc. of the vinegar. 



1 7 TOTAL ACIDS.-TENTATIVE. 



Dilute 10 cc. of the sample with recently boiled and cooled water until it appears 

 very slightly colored, and titrate with N/2 alkali, using phenolphthalein as an 

 indicator. One cc. of N/2 alkali is equivalent to 0.030 gram of acetic acid. 



1 8 FIXED ACIDS.-TENTATIVE. 



Measure 10 cc. of the vinegar into a 200 cc. porcelain casserole, evaporate just to 

 dryness, add 5-10 cc. of water, and again evaporate; repeat until at least 5 evapora- 

 tions have taken place. Add about 200 cc. of recently boiled and cooled water and 

 titrate with N/10 alkali, using phenolphthalein as an indicator. One cc. of N/10 

 alkali is equivalent to 0.0067 gram of malic acid. 



19 VOLATILE ACIDS.-TENTATIVE. 



To obtain the volatile acids subtract the fixed acids, calculated as acetic acid, 

 from the total acids. 



