Proceedixgs of the Polytechnic Associatiox. 821 



tlie leaves of the maple, birch, and oak, will furnish a decoction for 

 tanning, more valuable in its results, than any other liquid. The 

 skins are prepared in precisely the same way as ordinary leather, and 

 the leaves are used promiscuously. Five pounds of maple leaves, from 

 decayed trees, to four gallons of water. The leaves and water are 

 reduced to five degrees by the barkometer. The leather made by this 

 process, is mainly used for upper leather, and appears very handsome. 

 For sole-leather the tanning has to be very hard. Mr. Tinkham also 

 exhibited a side of calf skin which had been tanned in three weeks. 



The Chairman remarked that the manufacture of leather was next 

 in importance and extent, to those of cotton, wool and iron. This 

 country produces more leatlier than any other. Both hides and tan- 

 ning bark were here comparatively cheap. The bark will grow more 

 scarce, as the oak and hemlock disappear, in bringing new soil under 

 cultivation. Some new source of tannin must be sought for, at no 

 very distant day. The amount of tannin in the leaves mentioned, is 

 extremely small. He found, on inquiry, that the specimens of leather 

 exhibited, were tanned by means of leaves, and japonica or other 

 material containing a large percentage of tannin. Pie feared the vir- 

 tue of dried leaves, in this case, had been over estimated. Analysis 

 of the leaf will settle the question. 



The Chairman explained an improvement in petroleum lamps, 

 made by the Rev. Dr. S. P. Grosvenor, of McGrawville, Courtland 

 county, N^. Y. Tlie specimen exhibited will show the manner in 

 which the inventor has prevented air from getting into the lamp 

 through the oj)enings in whicli the wick elevator moves. The inventor 

 could not be present this evening, but he informs ns that his main 

 object was to guard against the explosions so common with the 

 ordinary burner. He found these to arise from an explosive gas 

 formed by a mixture of the vapor of the oil with atmospheric air. 

 Hence he has taken great pains to make his burner perfectly air tight. 

 He has found that the admission of air is not necessary to the opera- 

 tion of his lamp. The space made vacant by the combustion of the 

 oil is filled by a non-explosive gas generated by the flame of the lamp. 

 Repeated experiments have assured him of this fact. As is often the 

 case, he was pleased to find that while obtaining his main object he 

 also had secured other important advantages ; the pressure upon the 

 surface of the oil M'as more constant than with the ordinary burner, 

 and hence the flame was more steady and uniform. He found too 

 that the oily vapor arising from ordinary lamps, causing a nauseous 



