74 REPORT — 1869. 



altered for zinc. Iron was rapidly oxidized in these experiments, tut none dissolved 

 in the water. Thames water containing a certain amount of sulphates and car- 

 bonates dissolved lead and union metal almost as well as pure distilled water did. 



i 



On some new substances extracted from the Walnut, 

 By Dr. T. L. Phipson, F.O.S. Sfc. 



"When the episperm of the walnut is digested for several hours in alcohol a yel- 

 lowish liquid is obtained, from which a new species of tannin, nucitannic acid, or 

 nucitannin can be procured. This is the principle to which the thin walnut skin 

 chiefly owes its disagreeable bitter taste. When it is boiled for eight or nine hours 

 with dilute hydrochloric acid, it jdelds, among other substances, glucose and an- 

 other acid, rothic acid, the composition and properties of which the author has 

 determined. Considerable quantities of ellagic acid and gallic acid are obtained at 

 the same time. 



Rothic acid is easily separated from these by a weak solution of ammonia, which 

 dissolves the new product, forming a purple red solution from which hydrochloric 

 acid precipitates the rothic acid. A second treatment yields it quite pure. 



Rothic acid is insoluble, or nearly so, in cold water, but dissolves somewhat in 

 hot water ; it is readilj' soluble in alcohol ; it forms a reddish-brown amorphous 

 substance, combining with ammonia, in which it is soluble, and with other alkalies, 

 but forming insoluble salts with lead, lime, and silver. Dried at 118° C. its com- 

 position was found to agree with the formula C^" H'^ 0'*. 



The lead-salt leaves metallic lead when calcined ; its composition was found to 

 be C-' H"^ 0'- 2PbO ; it is insoluble in cold acetic acid. The lime-salt contains only 

 1 equivalent of base, C^'* H'^ 0'- CaO. The rothates of soda, potash, and ammonia 

 are soluble. The salt of silver is a fawn-coloured precipitate, becoming darker on 

 drving, but is not reduced, and does not appear to be very sensitive to the action 

 of light. Rothic acid belongs to a somewhat numerous group of substances, and is 

 evidently related to gallic acid, ellagic acid, and rufigallic acid : — 

 Q23 H'^ 0^2=1 equiv. of Rothic acid. 

 Q28 ^12 02» = 2 equivs. of Gallic acid. 

 ^28 JJ6 O'^^il equiv. of Ellagic acid. 

 C28 JJ8 01^=2 equivs. of Rutigallic acid. 



The last of these is similar in many respects to rothic acid, but difiers in its 

 colour and that of its solutions, as well as by its composition. 



Nucitannin, from which rothic acid is derived, has not yet been submitted to 

 analysis. 



On a Specimen of Obsidian from Java. 

 By "WiiLiAM Chandler Egberts, F.C.S., F.O.S. 



This paper, which was illustrated by numerous di'awings and microscopical 

 specimens, was intended to demonstrate the extreme importance of microscopical 

 examination of rocks and minerals. 



The specimen of obsidian was from Java, but the exact locality is unknown. 



Examination with a 1-inch objective revealed the presence of three distinct 

 minerals. These were diopside, orthoclase,and magnetic iron. Each of these was 

 beautifully crystallized. The optical properties of the orthoclase crystals were 

 minutely given, but without drawings it is impossible to describe them here. 



The obsidian contained fluid-cavities, but unlike many specimens of obsidian 

 from other localities, it was free fi-om occluded gas. 



On the Measurement of Gases as a branch of Volumetric Analysis. 

 By W. J. EussELL, Ph.D., F.C.S. 



The object of the paper was to show that many quantitative determinations 

 could be made with great ease and accuracy by measuring the volume of gas 

 evolved in certain reactions. A specimen of calc-spar ga-se a volume of carbonic 



