252 ANNUAL OF SCIENTIFIC DISCOVERY. 



so acts upon them as to give them an exceedingly pliable yet firm basis, and 

 so prepares them that the strongest liquors of oak or hemlock, &c., may after- 

 ward be applied without binding or injuring the hides." 



"We have been assured, says the editor of Hunt's Merchant's Magazine, that 

 the sole leather made from this process, from sweated Buenos Ayres hides, 

 will make sewed work equally as well as the limed slaughter hides. The 

 leather is also tough and strong. The length of time required for tanning a 

 dry Buenos Ayres hide is ninety days, with 75 per cent. gain. The time re- 

 quired for tanning an Oronoco hide is much less, with a gam of 80 or 85 per 

 cent. This method will tan slaughter sole leather in thirty days: harness or 

 upper leather in the rough in twenty days, and calf-skins hi from six to twelve 

 days. 



MANUFACTURE OF GLUE FROM OLD LEATHER. 



J. H. Johnson, of London, has obtained a patent for preparing old leather 

 scraps to render them fit to be made into glue. The leather is first chopped 

 into small pieces and thoroughly washed, then placed in vats where it is di- 

 gested with a potash or soda. It is taken out, after a few hours, and subjected 

 to pressure, and again immersed in a stronger alkaline solution for some hours, 

 which processes remove all the tannic acid. It is now taken out and washed 

 well with water, and submitted to a steep of a very weak sulphuric acid for 

 twenty-four hours, to remove all the coloring matter. This being accom- 

 plished, it is again submitted to a weak alkaline solution of the carbonate of 

 soda, then washed in water, and is fit to be made into glue by the common 

 process. 



ON THE ACTION OF GALLIC AND TANNIC ACIDS ON IRON AND 



ALUMINA MORDANTS. 



Mr. Calvert, hi a communication on the above subject to the British Asso- 

 ciation, drew the following conclusions : 1st. That there can be no doubt 

 that tannic acid is the matter in tanning substances which produces black 

 with iron mordants. 2ndly. That the reason of gallic producing no black dye 

 is, that it reduces the peroxyd of iron in the mordant, forming a colorless and 

 soluble gallate of protoxyd of iron. Srclly. That gallic acid has the property 

 of dissolving hydrate of alumina, and also of separating alumina mordants 

 from the cloth on which they are fixed. 4thl} r . That the reason of extracts 

 of tanning matter losing their dyeing properties is, that the tannin is 

 transformed into gallic acid. 5thly. That gallic acid possesses the property 

 of dissolving iron, and thus lays claim to the character of a true acid ; while 

 tannin, not having this action, appears to me to be in reality a neutral sub- 

 stance. 



ECONOMIC APPLICATIONS OF BENZOLE. 



English patents have recently been granted to Mr. F. C. Calvert for the 

 employment of purified benzole, or coal naphtha, for the removal of paints, 



