1 56 Intelligence and Miscellaneous Articles. 



brown, and metallic silver is precipitated; with protonitrate of mer- 

 cury it gives an orange yellow precipitate, which becomes gra- 

 dually of a dirty green colour. 



When pyrogailic acid is slightly heated with concentrated sul- 

 phuric acid, it does not impart any particular colour, and is not sen- 

 sibly decomposed, which is rather a remarkable circumstance. 

 Purified gallic acid was treated in the same way, with the intention 

 of discovering a tanning matter : the acid assumed a fine purple 

 colour, which disappeared on the addition of water, and crystallized 

 gallic acid was precipitated. If the solution of gallic acid in sul- 

 phuric acid be exposed to a greater heat, part of the purple colour 

 yet remains; but almost the whole of the gallic acid is converted 

 into a powder of a fine brown colour, which has the characters of 

 ulmin, and without the development of tanning matter. 



The compounds of pyrogailic acid with bases were not examined^ 

 except the pyrogallate of alumina, which is easily obtained by dis- 

 solving freshly precipitated gelatinous alumina in pyrogailic acid. 

 A very acerb liquor is formed, which is rendered turbid by heat, and 

 becomes transparent again on cooling, precisely like acetate of 

 alumina. It produces an exceedingly abundant white coagulum 

 with gelatin. The pyrogallate of alumina is capable of being cry- 

 stallized. It appears to redden litmus paper even more strongly 

 than the acid itself, as if the alumina in this case also acted like an 

 acid. The gallate of alumina also possesses properties similar to 

 those just described. 



According to the opinion expressed by Berzelius, that which 

 chemists have imagined to be pure gallic acid contains much 

 tannin ; endeavours were made to combine the latter with the sub- 

 limed acid, with the intention of reproducing a substance similar 

 to gallic acid ; but every effort was unsuccessful. 



From the observations which have been detailed, M. Braconnot 

 concludes : 



ist, That gallic acid obtained in the humid way, and properly 

 purified by animal charcoal, may be considered as pure and un- 

 mixed ; 



2ndly, That when it is exposed to heat it is converted into a 

 tanning matter and pyrogailic acid ; 



3rdly, That on combining the latter with tannin, gallic acid can- 

 not be reproduced. — A7in. de Cliim. xlvi, p. 206. 



ANALYSIS OF TENNANTITE. 



To the Editors of the Philosophical Magazine and Aivials. 

 If the subjoined analysis of an ore of Tennantite copper from a 

 recently opened mine is worthy of insertion in the Philosophical 

 Magazine, it is at your service. I confess, I regret deeply that the 

 mineralogical knowledge which was formerly attainable from your 

 magazine has recently fallen off. Why do not Dr. Turner, Mr. 

 Heuland, Mr. Brooke, and others, step forward to communicate the 

 knowledge they possess and keep up the zest for so interesting a 



science ? 



