54 JOURNAL OF THE 



Exhaust 0.8 gram oak bark with boiling water, and make it 

 up to 500 cc. with cold water. 



Place six two-ounce clear glass tumblers (or beaker glasses) on a 

 white surface, and in one of them, loith a dropping pipette (about 

 four inches long and one-quarter inch wide) about half filled, put 

 five drops of the infusion of bark, and in the others, toith the same 

 jnpette (after rinsing), put 4, 5, 6, 7 and 8 drops of the "tannin 

 solution.^' (The drops of the infusion and of the tannin solu- 

 tion must be uniform. The use of the same pipette, about half 

 filled, insures that). 



Now, add to each 5 cc. of "iron mixture," and in about one 

 minute add to each tumbler about 20 cc. water, and within three 

 minutes observe the shades of color. The number of drops of 

 "tannin solution'^ used in the tumbler which corresponds in 

 shade of color to the tumbler containing the infusion of bark 

 indicates the percentage of tannin in the hark; i. e., if it is the one 

 in which seven drops were placed, the tannin strength of the 

 bark is seven per cent. 



It is best to observe the shades of color horizontally, rather 

 than vertically, and to hold up the infusion tumbler, with the 

 one which most nearly corresponds, opposite to a white wall, 

 with vour back to the hVht. 



The above is written for oak bark, but the same process will 

 answer for any substance containing less than ten per cent, of 

 tannin. 



For substances containing between about 10 and 20 per cent., 

 it is best to dilute the infusion with an equal part of water and 

 proceed as above, using five drops of the dilute infusion, and for 

 the answer double the result. Thus, if the diluted infusion of 

 tea required eight drops tannin solution to correspond, call the 

 percentage sixteen. 



For substances containing less than one, or one and a half per 

 cent., exhaust 8 grams instead of 0.8 gram, and take one-tenth 

 of the result for the answer. For substances containing more 

 than twenty per cent., as galls, sumach, catechu, etc., you may 

 dilute the infusion with two, three or more times its bulk with 



