268 Crace Calvert on the 



in the hope of discovering a substance, which would act as an 

 antiseptic to this peculiar fermentation, for the researches of 

 Messrs Delaroque and Robiquet junior have clearly shown that 

 tannin is transformed into gallic acid, and a substance resem- 

 bling sugar, under the influence of a peculiar ferment called 

 pectase. 



My investigations led me to discover three substances, which 

 possess the property of preserving from fermentation, tan- 

 ning extracts having a specific gravity 1*250, and as I trust 

 that the employment of these substances will facilitate manu- 

 factures and cheapen production, I do not hesitate to publish 

 them. They are chloride of lime, bichloride of mercury, but 

 especially carbolic acid, and to show the efficiency of this acid, 

 I may add, that I have an extract of sumach, which was mixed, 

 twelve months since, with a few per cent, of this acid, and 

 which is as sound as when mixed. The first two substances 

 answer very well, but the last has the great advantage of not 

 interfering with the general applications of the extract of tan- 

 ning matters. 



The remarkable power of dissolving the hydrates of oxides of 

 iron and aluminum possessed by gallic acid, induced me to try 

 its action, as well as that of tannic, on metallic iron. For this 

 purpose, 1000 grains water, 25 grains acid, and 100 grains 

 iron-wire were introduced into tubes, so arranged as to convey 

 the gases evolved to the pneumatic trough, care being taken 

 to exclude all air. After a few days, it was found that several 

 cubic inches of gas had been given off from the gallic acid 

 tube, which, on testing, proved to be nearly pure hydrogen, 

 whilst the liquor remained colourless, and only assumed a 

 slight blackish-blue tint, when exposed to the air. The iron 

 on being taken out, was carefully dried and weighed, and 

 found to have lost 1-4 grains. Therefore, gallic acid has the 

 property of dissolving iron. It was also observed, that in the 

 case of the tannic acid, no gas was evolved, neither was iron 

 dissolved ; although the solution had assumed a slight purple 

 tinge, which I attributed to some trace of oxide produced on 

 the bright surface of the wire, during its weighing. I also 

 tried a similar series of experiments, substituting for the 1000 

 grains water, 1000 grains of a solution of sugar, having a spe- 



