AMERICAN INSTITUTE. 645 



carefully. They differ much in strength, and some are liardly 

 manageable, splitting when they cool. I have found it difficult to 

 cast perfect railroad wheels, on account of the unequal cooling of 

 the several parts thereof. I have confined the rims in iron rings, 

 wliich chills the exterior part of the wheel. I have found that 

 by mixing several sorts of iron together, I improved all my 

 castings. 



The Secretary desired Mr. Mott to speak of the progress of our 

 iron masters in hollow ware, a question of deep interest years ago 

 and now. 



Mr. Mott — We have made for several years strong and light 

 hollow ware, equal in all respects to the best made in Scotland or 

 elsewhere. My bathing tubs for adults, full size, are of cast iron, 

 and weigh but two hundred pounds ; they are but one-eighth of 

 one inch thick. I have cast them one-sixteenth of an inch thick, 

 and they buckle and bend almost like sheet iron. I have often 

 used Scotch iron in my works heretofore, but none since last 

 March. 



Mr. Tillman adverted to the unequal dilation and contraction 

 of iron and other metals. Zinc is remarkable for its great con- 

 traction in cooling. Car wheels of 60 to 100 different forms have 

 been made Avith curved radii and otherwise; but tliere is always 

 difficulty on account of unequal cooling of the different parts of 

 the wheel. 



Mr. Mott — Cores of sand, with some vegetable matter in them, 

 as rye flour for instance, makes the core sufficiently fine, and the 

 flour being burned by the melted iron, makes the necessary room 

 for the contraction on cooling. American iron is tlie strongest. 

 On melting the Scotch iron, I lose eleven per cent of it. but of 

 our American iron, only from one to six or seven per cent. By 

 the cold blast, I melt about six pounds of iron with one pound of 

 coal. 



Mr. Devyr, of Brooklyn, asked — Why not use cold air on the 

 various parts of a cooling casting so as to cool all tlie parts 

 equally? 



Mr. Butler had sometimes found the plates he uses in the con- 

 struction of liis iron safes, burst in cooling, and fly some distance 



