242 Chronicles of Science. [April, 



We gaye in our last, a process by Dr. Wagner, for estimating 

 the gallotannic acid in tanning materials. Another process has since 

 been published by R. Pibram,* who exhausts the material to be 

 examined with boiling water, niters the liquor, and precipitates with 

 a solution of one gramme of sugar of lead in fifty grammes of 

 water. The precipitate is collected on a weighed filter, carefully 

 dried at 120° C, and then weighed. It may now be ignited in a 

 porcelain crucible, and the tannin estimated by difference. This 

 method is simple, and will probably give sufficiently accurate results 

 for trade purposes. 



We may mention here, a critical examination of some of the 

 published processes for the estimation of Tannin, by Mr. John 

 Watts,t who gives the preference to the process of Mittenzwey. 

 This is an application of the well-known fact, that an alkaline solu- 

 tion of tannin will rapidly absorb oxygen. We must refer the reader 

 to the original paper for a full description of the process ; but as 

 some may be employing it, we must mention a correction made by 

 Mr. Watts. Mittenzwey states that a gramme of tannin absorbs 

 175 ccs. of oxygen at 20° C. Mr. Watts, however, has ascertained, 

 by repeated experiments, that the volume of oxygen actually 

 absorbed is 231 ccs. 



The length to which our notice of the Chemical Society extends, 

 obliges us to omit any other matters, which would otherwise have 

 found a place. 



Proceedings of the Chemical Society. 



At the meeting held on December 6, Mr. E. T. Chapman read 

 a paper " On the Synthesis of Formic Acid." Struck by the fact 

 that by oxidation acetate of ethyl yields two equivalents of acetic 

 acid, Mr. Chapman came to the conclusion that nascent oxygen 

 could not be the sole agent in effecting the change. In the case 

 mentioned there is the same amount of hydrogen in the products 

 obtained as in the substances operated upon. From this it would 

 appear that either the ethyl had given up a portion of its hydrogen 

 to the residue of the acetic acid, and then appropriated to itself two 

 equivalents of oxygen, or that the acetic ether had been decomposed 

 by the assimilation of water and the substitution of oxygen for 

 hydrogen, which amounts, in fact, to the action of hydroxyl and 

 the direct addition of hydrogen. The author believes that in most 

 cases of oxidation of organic bodies this substitution of hydroxyl for 

 hydrogen, or its super-addition, takes place. The synthesis of 

 formic acid seems a direct proof of this. When finely-divided 

 carbon (lamp-black) is boiled with permanganate of potash and 

 sufficient sulphuric acid to liberate the permanganic acid, formic 



* Wittstein's ' Vierteljahrsch,' 15, 520. 

 f 'Pharmaceutical Journal,' March, 1867. 



