166 



Mr. Mallet on the Physical Conditions 



Table II. 



S/iomng the decrease of Specific Gravity, due to increase of bulk, of Iron Castings made from 

 the same sort of Cast-Iron, and under similar circumstances. 



57. For the relations that both head and bulk of casting appear to bear to 

 strength, see the observations at page 270, Report (m< supra). Fineness of 

 grain, smallness of crystal, density, increased cohesion and elasticity, and 

 diminished corrodibility by chemical agency, all are induced by casting under 

 largely increased statical heads of fluid metal. Let us hope so evident an 

 improvement may no longer be neglected in our gun-foundries, where, by 

 apparatus not difficult to contrive, atmospheric pressure, or that of condensed 

 air, might easily be brought to aid that of the head of metal, with economy in 

 reducing the labour and cost of the mass of metal to be melted, and with the 

 advantage of enabling the pressure on the solidifying mass to be varied, or 

 repeatedly increased per salfum, so that by a certain amount of regulated mo- 

 mentum, the consolidating particles should be pressed and shaken into contact. 



7. — Quality of Metal. 



58. The repeated failures of cast-iron ordnance latterly, and a very imperfect 

 and uninformed appreciation either of the causes, or of the respective qualities of 

 various " makes" of cast-iron, have induced the belief and expression of doctrine 

 " on authority," that the failures have been owing to the use of British makes 

 of cast-iron; that smelting with pit coal produces effects highly injurious to 

 the tenacity of the pig-iron, &c., &c. ; and that the remedy is to be sought in 

 the employment of foreign cast-iron, smelted with charcoal only, such as that 

 of Nova Scotia or Sweden ; and a certain plausibility is given to this half-fledged 



