Proceedings of the Polytechnic Association. 1039 



Dr. P. H. Yanderweyde. — I can corroborate what tlie gentleman has 

 said in regard to the conducting power of clay cells. In some expe- 

 riments which I made with Mr. Chester, we found that clay cells 

 might conduct electricity too freely and we found an advantage from 

 drawing a line of varnish spirally around the cell, thus diminishing 



its conducting power. 



Adjourned. 



April 1, 1869. 



Professor 8. D. Tillman in the chair ; Mr. C, E. Ehkry, Secretary. 



Dr. L. Feuchtwanger exhibited several specimens of sand and 

 sandstones, such as silica, elastic sandstone, Devonian sandstone, rock 

 crystal or Brazillian pebble, quartz from the Pyrenees and the Alps, 

 agates, Arkansas stone or hornstone, onyxes, sea and river sand ; also 

 sticks of glass in which several colors were combined, a plate of look- 

 ing glass silvered with the nitrate of silver, white glass made of 

 cryolite and felspar, sometimes called porcelaine, corundrum, which 

 is next to the diamond in hardness, and used much in rock drilling. 

 The doctor then read the following paper : 



Sand, Geologically, Chemically axd Technically Considered. 

 Dr. Lewis Feuchtwanger.— Sand is the term generally applied to 

 all powdered stone, but pure sand consists of particles of quartz, silex 

 or silica, which is composed of silicon and oxygen ; and its chemical 

 symbol, under the new atomic weight given to silicon, is Si. Oj. 

 These particles, which are more or less rounded, are of a white, gray 

 or grayish red color, and are unquestionably derived originally from 

 a compact rock, called the sandstone formation. Sand may, however, 

 be granitic, containing particles of felspar. This is the case when it 

 has not been exposed to atmospheric agents long enough to decom- 

 pose it. Sand consisting of angular grains is mostly employed for 

 mortar or building purposes. The rock called sandstone is made up 

 of agglutinated sand or pebbles and fragments of the same. It may 

 be a siliceous, granitic, porphyritic, basaltic or calcareous sandstone, 

 according to the material which occurs with it in nature ; and it may 

 be a compact, friable, ferruginous or concretionary sandstone, accord- 

 ing to its structure. Again, if the sandstone glistens with scales of 

 mica, it is called a micaceous sandstone ; if much clay is mixed with 

 the sand, it is called an argillaceous sandstone ; and if this contains 



