640 TRANSACTIONS OF THE 



at a high elevation, will be found the same, or very nearly the 

 same, at opposite sides in every part of their length. 



Loam moulds are made in boxes or shells, differing in form 

 from those required for sand moulds, and are formed by a sweep 

 attached to a revolving axis; the sweep having a profile identical 

 with the exterior line shown by a longitudinal section of the pipe. 



The moulds, after being " swept up," are finished, black washed, 

 dried and treated in all respects, in the same, or nearly the same, 

 manner as dry sand moulds. The pipes, whether cast in dry 

 sand or loam, should in all cases be allowed to remain in the 

 moulds, unopened and undisturbed, until nearly or quite cold, in 

 order that they may retain the correct form they receive from the 

 moulds, and be preserved from the strains produced by the irregu- 

 lar contraction, which results from uncovering and exposing the 

 heated metal directly to the cooling action of the atmosphere. 

 Pipes cast in moulds, and upon cores thus prepared, and allowed 

 to cool before they are removed, are found perfect in form, and 

 have a surface, or as the workmen term it, a" skin," entirely free 

 from sand, internally and externally, and which resists oxidation 

 much longer than the surfaces of castings made in green sand. 

 Their superiority to those cast in green sand, may be summed up 

 as follows : 



1st. Loam and dry sand pipes, cast vertically or at a high 

 angle, have the metal equally solid on all sides, and are conse- 

 quently free from the imperfections generally found on the upper 

 sides of those cast horizontally, as green sand pipes must be, in 

 consequence of the weakness of the molds; they are therefore 

 stronger than green sand pipes of equal weight; the upper and 

 lower sides of which almost invariably differ in thickness; and 

 the thinest part determines its strength and durability, and con- 

 sequently its value. 



2d. Being more regular in thickness, they are more uniform in 

 weight, and the required strength and durability are obtained, 

 with the minimum expenditure of matf>rial. 



3d. Being smoother and having surfaces less susceptible of 

 injury by the action of air or water, than those cast in green 

 sand, pipes of equal weight, will for these reasons be more durable. 



