432 TRANSACTIONS OF THE 



The fact mentioned by Mr. Butler, that to secure good castings it was 

 necessary to fuse three varieties of iron together, seems to favor the theory 

 that the differences between wrought iron, cast iron, and steel are produced 

 by chemical changes. It is probable that a slight amount of some unknown 

 element is necessary in castings, and by mixing the three varieties of iron, 

 together this was more likely to be secured then if only one variety of iron 

 were used. The effect produced by the presence of a very small amount 

 of an element is seen in the great change produced in carbon by the pres- 

 ence of a small percentage of iron-forming graphite. That portions of 

 wrought iron can be brazed together, while pieces of cast iron can not, may 

 be due to the same principle ; the action of a small portion of some ele- 

 ment. Brazing is a mode of employing the force of adhesion, which acts 

 only between certain substances chemically unlike, but having some affin- 

 ity for each other. Affinity is necessary to adhesion, but still it is quite 

 distinct from cohesion. The adhesion of the brazen solder to wrought iron 

 and not to cast iron indicated a chemical difference between the two states 

 of the iron. 



Mr. Tillman. — The Chinese are said to be able to mend east iron with- 

 out the interposition of wrought iron. 



The Chairman. — Our friend, Peter Cooper, had much to contend with 

 in his iron works before success attended him in this department of his un- 

 dertakings. His attention having been called to the necessity of removing 

 the zinc from combination with the iron, he followed the hint, his works 

 became profitable, and his iron unsurpassed. Vast sums of money have 

 been worse than wasted by persons embarking in the iron trade, and not 

 taking in the bearing of commerce, and other forms of industry, upon their 

 enterprise. Even at Scranton the fires could not have been kept in one 

 da}', had they to depend solely upon the iron trade. At Poughkeepsie, 

 with strict economy, and close attention to the wants of the community, we 

 are enabled to produce iron without loss to the proprietors. 



On motion of Mr. Tillman, the Association adjourned to Thursday even- 

 ing next, to meet in room 24, 



Polytechnic Association of the American Institute, 



May 2Qth, 1859. 



S. J). Tillman, Esq., in the chair. John Johnson, Esq., Secretary pro 

 tem. 



Dnring the time devoted to miscellaneous business, the Secretary 

 described Mr. Corvell's new method of obtaining aluminum. " He washes 

 the clay and frees it from all foreign substances. He next dries the clay 

 and adds to it concentrated sulphuric acid to remove sulphate of iron. He 

 then allows it to settle, and having poured off the acid, dries the residuum, 

 after which he heats it to about 600^ Fahrenheit. Three ounces of the 

 clay so prepared, is next mixed with six ounces of pulverized yellow prus- 



