The estimation of tannin in wines, where considerable accuracy is required, may be made by the permanganate and indigo method, which has been so much discussed and modified in chemical literature. The following approximate method is given by the Berlin Commission:

In 10cc. of wine the free acids are, if necessary, reduced by the addition of standard alkali solution to .5 grains in 100cc. Then 1cc. of a 40 per cent. solution of acetate of soda is added, and finally, drop by drop, 10 per cent. solution of chloride of iron, avoiding an excess. One drop of the chloride of iron solution suffices for the precipitation of about .05 percent. of tannin.

For the estimation of the bulk of the precipitate test-tubes are used, which are much narrowed at the bottom, with the constricted portion graduated into tenths of a centimeter. The following table gives the approximate content of tannin from the bulk of the precipitate after standing twenty-four hours:

I can see no practical conclusions to be drawn from so indefinite a determination and have omitted it in my work, simply quoting it for the benefit of any one who might desire to make the estimation.