AMERICAN INSTITUTE. 639 



little tenacity possessed by sand, when in proper condition to 

 receive tlie melted metal with safety, renders these molds too 

 weak to sustain tlie j)ressure to which the lower portions would 

 be subjected, if, when the castings were made, they should be 

 placed vertically, or indeed in any other position than nearly or 

 quite horizontal. 



When cast in " dry sand," in suitable boxes, tliey may be molded 

 from iron patterns, cast and turned to the proper size and form; 

 the material composing the molds, which is a mixture of coarse 

 sand and clay, may be much harder rammed than green sand will 

 admit, with safety, and the patterns may be turned about in the 

 moulds before thay are parted, thus insuring perfection in the 

 external form, and accuracy in the size and position of the prints, 

 which receive and retain the cores upon which the interior of 

 the pipes are formed. 



After the patterns are drawn, the moulds are finished, and 

 receive a coat of " black wash," composed of powdered charcoal 

 and water, in whicli there is generally mixed a small proportion 

 of tine clay, or sometimes molasses, to render it adhesive. This 

 is laid on with a soft painter's brush, or a swab made of raw flax 

 or fine soft hemp. The molds are then made perfectly dry, 

 care being taken not to raise tlie heat so high during the opera- 

 tion as to burn the charcoal blacking. 



The cores are made of loam, laid upon a straw rope, wound 

 about a strong hollow^ core bar, fitted wath an axis, upon which it 

 is made to turn, in order to give the plastic loam its proper form. 

 These, when truly formed, arc also finished with a coating of 

 black w"ash, and are dried in the same manner as the molds. 



The core bars used for pipes cast in dry molds should have 

 the bearings at the faucet ends turned, to precisely fit the print 

 made by the pipe pattern, and this furnishes to the workmen an 

 unvarying guide for the size of that end of the core; thereby 

 insuring uniformity in the diameter of the faucets, and more 

 regularity in weiglit than is generally found in pipes cast in green 

 sand, and especially those made upon green sand cores, as is 

 sometimes done. If all the operations in this mode of casting, 

 are properly conducted, the thickness of those cast vertically, or 



