28 



with 95 per cent alcohol; dry at a moderate heat for a few minutes, cool and weigh. 

 Calculate the amount of lead in the precipitate (factor 0.6829) and subtract this from 

 the amount in 2.5 cc of the standard solution as determined on a blank test, and divide 

 the remainder by 0.125, thus obtaining the lead number. 



The standard lead eubacetate used in this work is prepared as follows: Dilute a 

 U S. P. lead subacetate solution until the specific gravity is 1.25; to one part of this 

 add four parts of water and filter. If the solution becomes cloudy, filter before using, 

 and determine its strength frequently. The referee found that the strength changed 

 but little. 



Mr. E. M. Bailey of the agricultural experiment station at New Haven, Conn., has 

 reported work which he did independently on different kinds of samples of vinegar 

 of known purity. He includes other data in his results, especially those on testing a 

 recent method for the determination of malic acid which was formerly applied to maple 

 products." He found that by using this method more malic acid can be recovered 

 than by the old calcium chlorid method. The method for determining the load 

 number is as follows: 



Measure 50 cc of vinegar into a 100 cc flask, add 25 cc of lead subacetate (dilute 

 solution used by Winton and Kreider) make up to the mark and filter. To 10 cc of 

 the filtrate add 1 cc of concentrated sulphuric acid, 40 cc of water and 100 cc of 95 per 

 cent alcohol. Filter after 12 hours, ignite, and weigh. 



The amount of lead in the blank test is determined by diluting 25 cc of the lead sub- 

 acetate solution to 100 cc; 10 cc are taken out and the lead number determined as in the 

 method just given. 



The modified method for malic acid as applied to vinegar is as follows: 



To 10 cc of vinegar add an equal volume of water, 3 cc of a 10 per cent solution of 

 calcium acetate, and 180 cc of 95 per cent alcohol. Heat on the steam bath for from 

 20 to 30 minutes, stirring vigorously at intervals to insure a clear supernatant liquid. 

 Filter on 589 S and S paper, wash with 85 per cent alcohol, and ignite. Dissolve in 

 excess of tenth-normal hydrochloric acid (10 cc) by gentle boiling, and continue to 

 boil for about 10 minutes. Cool and titrate with tenth-normal sodium hydroxid, 

 using methyl orange as indicator. 



The results of the work of the referee and those of Mr. Bailey appear in the accom- 

 panying table. This shows the variation in the amount of lead precipitated by the 

 different vinegars. In the case of malt vinegar, the results tend to run high; while 

 those of the sirup and distilled vinegar are very low. 



It should be noted that in the case of malic acid determinations, which are, of 

 course, not properly such on malt and sirup vinegar, misleading results may be ob- 

 tained and, in the case of a suspected sample, the malic acid determination would 

 have to be confirmed by the procedure recommended by Leach and Lythgoe.& 



In comparing the figures for malic acid, phosphates, and the lead number as worked 

 out by Mr. Bailey, it is his opinion that a closer relation exists between the phosphate 

 content and the lead number than between the malic acid value and the lead number. 

 The three highest lead numbers are associated with the three highest total phosphate 

 values; the same is true of the three lowest figures in each case. That this does not 

 follow, however, in the case of lead numbers and malic acid values would seem to 

 indicate that the precipitate produced on adding lead acetate to vinegar is due rather 

 to the phosphates than to the malates. This is in accordance with the statement of 

 Leach and Lythgoe c that the precipitate produced by lead acetate is not entirely due 

 to malic acid. Tolman and Le Clerc d are also of this opinion. 



The other data for pure cider vinegar, included in the table, are fairly typical, and 

 in addition to the old figures the new ones for the lead number are of interest. 



<* J. Amer. Chem. Soc., 1908, 30 : 1285. 



b J. Amer. Chem. Soc., 1904, 26 : 379. 



< J. Amer. Chem. Soc., 1904, 26 : 380. 



<*U. S. Dept. Agr., Bureau of Chemistry, Bui. 99, p. 89. 



