1S4 Observations on some Points [Margh, 



This compound is white ; and, when dried, it becomes greenish ; 

 but I have never obtained it of the same degree of saturation when 

 prepared by different processes. The tannin in it was ahvays com- 

 bined with more than l-i- times as much base as in the neutral 

 tannate ; though it never contained so m.uch as twice that quantity. 

 I analyzed tannin by employing for the combustion both super- 

 tannate and tannate as neutral as possible, and the analyses fur- 

 nished the same result : 0-4 of tannin produced 01425 water and 

 0'7C25 carbonic acid. Hence tannin of nutgalls is composed of 



Hydrogen 4-186 



Carbon 51-160 



Oxygen 44*654 



100-000 



But we have seen that 100 of tannin combine with 52 oxide of 

 lead, the oxygen in which is 3-718. Now 3*718 x 12 = 44-616. 

 Hence we may conclude that tannin contains 12 volumes of oxygen. 

 But there is no doubt that there must be an analogy between gallic 

 acid and tannin, and this analogy can scarcely be any thing else 

 than the same compound radicle combined with different volumes 

 of oxygen. Supposing, then, that tannin, like gallic acid, contains 

 equal volumes of carbon and hydrogen, and that it is 12 O + 

 18 C + IS H, or (which comes to the same thing) 4 O + 6 C + 

 6 H-, its composition ought to be per cent. 



Hydrogen 4*45 



Carbon 50*55 



Oxygen 45*00 



100*00 



Here we find a little more hydrogen and a little less carbon than 

 the analysis indicates. This is a necessary consequence of the dis- 

 hydrogenation which tannin undergoes by exposure to the air, in 

 consequence of which the colour of its combinations becomes 

 darker and darker ; so that we never can procure this substance in 

 a perfect state, excepting in fresh nutgalls in which the tannin is 

 not yet coloured. 



{To be continued.) 



Article IV. 



Ohservations on some Points co7inecied with the Atomic Theory. 

 By Thomas Thomson, M.D. F.R.S. 



Profkssor Berzklius, having in his important dissertations on 

 this subject published in the second, third, fourth, and fifth 



