SOME ASTRINGENT SUBSTANCES, ETC. 231j 



left in the two solutions at the end of a week, is very small, and in one case 

 only, that of Myrobalans, has the solution digested on the residue lost most. 

 Our experiments prove that there are substances present in the solutions 

 which influence the decomposition of the tannine, and that in diffe- 

 rent solutions it decomposes with very different degrees of rapidity. As an 

 example, Terminalia angustifolia lost l7 - 46 parts of tannine out of 40 - 66 ; 

 now if the action was due merely to atmospheric influence, we should 

 naturally expeet that, supposing no other principle was at work, the 

 quantity lost under similar circumstances by different solutions, would be 

 in direct proportion to this, but we do not find this to be the case ; for in 

 order to agree with it, Valonia should lose 16 - 31 parts of tannine out of 

 37"98, but it only lost 5 - 28. Japan galls, again, containing 76 - 59 per cent, 

 of tannine, only lost 9*1 per cent, or a little more than a quarter of that lost 

 by T. angustifolia. It is evident that this principle, whatever it isj is 

 soluble, for the difference in the loss between the solution standing by itself 

 and that on the residue is so small as, in a case like this, to be unimportant. 



To extract the tannine, the barks were cut into small pieces, and were 

 treated in the following manner : — 



About 2,000 grs. of cold water were poured on the weighed quantity, and 

 allowed to digest for about two hours, frequently stirring ; in the meantime, 

 the clear solution was poured off, and the residue treated with a similar 

 quantity of water for about three hours ; this solution was decanted, and 

 3,000 grs. of water poured on the bark and left all night ; this solution was 

 taken off in the morning, and 2,000 grains more of water poured on, at the 

 end of an hour this was mixed with the solution already obtained, and 

 made up to 10,000 grs. To make sure of extracting all the tannine, 5,000 grs. 

 of water were allowed to remain on the residue for twenty-four hours, and 

 then about half an ounce of the liquid was tested with the gelatine solution ; 

 if no precipitate occurred, it was thrown away, but if there was any, it was 

 estimated, and the product added to the first quantity. 



In the gall nuts, which contain a very large quantity of tannic acid, much 

 difficulty 'was experienced in exhausting them ; the ether process, as re- 

 commended for the preparation of pure tannic acid, was tried, but not 

 found to answer. We consider the following to be the best plan : — Take 

 about 10 grs. of the finely pulverised galls, treat them with warm water, 

 allow the infusion to stand for some time, filter off through linen, carefully 

 wash the residue back into the beaker ; continue these successive digestions 

 until a few drops of the filtrate leave a very slight residue on evaporation ; 

 lastly, boil the residue with water to make sure of extracting the last traces 

 of tannine, and make up the solution to any convenient standard. 



We shall now proceed, in the following pages, to give in detail the results 

 of our various experiments : 



