PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 885 



lime are required to decompose 100 of cryolite. The sediment is 

 separated, and the lye, standing 20° B, is treated with carbonated 

 soda-lye and steam ; the lime and alumina are separated by car- 

 bonate of soda, and pure alumina will settle down. 



The dry process consists in calcining 150 lbs. of chalk with 100 

 lbs. of crj'olite, in a peculiarly constructed oven for two hours; 

 whereby, again, the carbonate of soda and alumina with soda and 

 fluoride are the results. The mass is lixiviated by water and steam; 

 a little caustic lye is added for the purpose of getting out all the 

 alumina, which may then be thoroughly separated carbonic acid 

 gas, obtained by the burning of coke in a draught of air brought 

 upon it by the aid of a centrifugal blower. 



After some discussion of the points presented in this paper, the 

 association adjourned. 



American Institute Polytechnic Association, 



March ^Wi, 1867. 



Prof. S. D. Tillman in the Chair; T. D. Stetson, Esq., Sec'y. 

 The meeting was opened with the following scientific news, pre- 

 sented by the Chairman : 



Glass as a Building Material. 



The whole amount of glass used in the Paris Exposition build- 

 ing would cover a space of 19^ acres. 



Annual Production of Diamonds. 



The total value of the diamonds yearly found throughout the 

 world, is estimated at $4,400,000. 



Electrical State of the Earth's Crust. 



M. Matteucci has discovered that if the surface of the earth be 

 connected at different altitudes by a conducting wire, a constant 

 current of electricity will flow from the lower to the higher 

 point of contact, the intensity of which will be in proportion to 

 the difference in altitude of the two points. Geological forma- 

 tions and atmospheric changes will, of course, modify this action. 



Immense Machines. 



Mr. Krupp, the proprietor of the celebrated steel works at 

 Essen, Prussia, is now engaged in constructing a plate mill, which 



