1000 FOODS AND FOOD ADULTERANTS. 
JOHANSON, E. A modification of Davy’s method, employing 5 to 8 drops of a solu- 
tion of chromic sulphate (one part in twenty-five parts water) per 100 ce of 
the glue solution. Chem. News, 50, 176. 
JACKSON, R. This method employs lead carbonate as a precipitant of tannin. The 
percentage of tannin is calculated from the density of the solution before 
and after the precipitation. An error is possible from the partial solution of 
the lead by a free organic acid. Chem. News, 50, 179; Zeitsch. f. anal. 
Chem., 24, 271. 
JEAN, F. A volumetric method based upon the fact that tannic and gallic acids 
combine with iodine, in the presence of sodium carbonate, in definite propor- 
tions. Filter paper covered with starch powder is used in testing for excess 
of iodine. The presence of gallic acid necessitates a second titration after 
the removal of the tannin by an appropriate precipitant. Ber. d. chem. 
Ges., 9,730; Zeitsch. f. anal. Chem., 16, 123. 
JEAN, I’. A colorimetric method, in which a tannin solution of known strength (1 
per cent) is added to a ferric chloride solution containing free hydrochloric 
acid, until a piece of white paper placed under the beaker on black cloth is 
no longer visible. A similar titration is made with a solution of the sample 
to be assayed. Two titrations are necessary, one before and one after the 
removal of the tannin by gelatin. Bul. Soc. chim. de Paris., 44, 183; 
Zeitsch. f. anal. Chem., 28, 108. 
KaTREINER. This chemist objects to the methods of Carpené and Barbieri, and 
states that the probabilities of error are great. Zeitsch. f. anal. Chem., 18, 
112. 
LOweE. In this method the infusion is evaporated with a few drops of acetic acid, 
and residue is then exhausted with alcohol, which dissolves the tannin only. 
The tannin is then estimated in the alcoholic solution. Jsb. d. Chem., 
18, 743. 
LEHMAN. ‘Titration with a glue solution containing ammonium chloride. Jahres- 
ber. d. Chem., 1881, 1206; Russ. Zeit. Pharm., 1881, 321. 
LOWENTHAL, J. This method is one of the most important yet devised for tannin. 
It is given in considerable detail, since a modification of this method is usu- 
ally employed in modern practice. See method as modified by Procter, 
Conneler, and Schroeder, page 890, this report. 
Vhe method devised by Lowenthal is based upon the oxidation of tannin by per- 
manganate of potassium. Four solutions are employed: (a) permanganate of potas- 
sium, standard solution; (6) 6 grams indigo, with 50 ce concentrated sulphuric acid 
per liter; (c) 25 grams white glue, dissolved in water and the solution saturated 
with sodium chloride, then made up to 1 liter; (d) a saturated solution of sodium 
chloride, with 25 ce sulphuric acid per liter. The sample is extracted in boiling 
water, the solution is cooled and made up to 1 liter. (1) 10 ce of this extract are 
diluted to 800 or 1,000 ce, 25 ce indigo solution added, and a titration is made with 
the permanganate. (2) 25 ce indigo solution are diluted to 800 or 1,000 ce. and 
titrated with permanganate. This burette reading is subtracted from that under (1) 
to obtain the net reading, i. e., the permanganate required for the tannin and gallic 
acid and other oxidizable matter in 10 ce of the extract. (3) 100 ce of the extract 
are now treated with 50 ce glue solution, and, after shaking, 100 ce salt solution 
are added. After several hours the solution is filtered. To 50 ce of the filtrate 25 
ee indigo are added and another titration is made. Under these conditions, again 
determine the permanganate required for the indigo and deduct the burette, reading 
as before. In the titration under (3) a volume of the solution equal to 20 ce of the 
extract was taken; hence divide the net burette reading by 2. This gives the per- 
manganate required to oxidize the substances other than tannin in 10 ce of the ex- 
tract. Deducting this last amount of permanganate from that required for all the 
oxidizable matter in the extract, and the remainder is that required for the tannin 
in 10 ce extract. 
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