AMERICAN INSTITUTE. 433 



side of potash and five ounces of common salt, and this mixture is raised to 

 a white heat in a crucible. The result is a beautiful white button of alu- 

 minum which is found at the bottom of the crucible. 



Mr. Seeley doubted the correctness of the statement that aluminum was 

 obtained by the process described. If it were true it was important for the 

 metal is now worth from four to five dollars an ounce. He would suggest, 

 as possibly a cheaper and more certain process, that chloride of aluminum 

 be employed with silver. 



Professor Hedrick considered the process suggested by Mr. Seeley to be 

 one of great importance. 



Mr. Coryelle wished to ascertain the best mixture for concrete for 

 houses. 



Professor Hedrick stated that in his opinion the only ingredients neces- 

 sary for concrete are lime and sand — one barrel of lime to twelve or fifteen 

 barrels of sand being the proportions. These form the cement and rough 

 stones may be used to any convenient extent for filling in. 



Dr. Vanderweyde. — If concrete is to be used under water, the lime of 

 which it is made, must contain some alumina, which gives mortar the prop- 

 erty of hardening under water. Hydraulic cements take a very long time 

 to consolidate entirely.* Indeed, no mortar becomes hard in all parts of 

 a building without a long lapse of time. In buildings which have fallen, 

 where the mortar had separated from the bricks, on a chemical analysis 

 being made of the mortar, it was found to contain all the ingredients of the 

 best quality of mortar, so that if it had sufiicient time, it would have be- 

 come durable and strong. 



Professor Hedrick stated that when cements set quickly, carbonic acid 

 plays but a trifling part. For foundations, where it was necessary to have 

 the mortar set soon, he has used common mortar mixed with cement. He 

 had used the kinds of mortar spoken of, but prefers coarse to fine sand. 

 He also mixes the mortar the day before it is required for use, and works 

 it up immediately before using, when to appearance it is nothing but sand. 

 With proper apparatus, walls ai'e speedily and cheaply built, and they 

 become hard and dry in the space of one month. The stones occur in the 

 concrete in every position and of all shapes and sizes, within moderate 

 limits. The appearance presented by the walls is pleasant. They are 

 smooth and perfect, and can be finished six months after being built, by 

 giving them a coat of " rough cast." The building alluded to, was erected 

 in North Carolina, and the weather there is as variable, and subject to as 

 great extremes as in New York. Moisture freezing within the walls and 

 again thawing is the chief cause of destruction to concrete walls. In 

 answer to a question, he further stated that his walls did not crack, and 

 that no walls will, if the foundation be good. The stones employed were 

 of any size and shape that would fit in the box or frame used in building. 



* This is not the case, when Puzzolana is used with a pure quick lime, or when the ocmont is 

 made of Sept aria. In both cases, the mixture will harden throughout, when under water, ia 

 a few days. — J. R. 



Am. Inst.J 28 



