426 Mr. Mallet on the Physical Conditions 



SECTIONS. PAGE. 



31 The breaking of the surface a fallacious test of proper temperature, 156 



32,33 E6Fects of contraction on cooling of mass on construction, 157 



34 And of sudden change of mass, 157 



35 Coefficient of lineal contraction, and for volume, 158 



36 Internal strains due to contraction, 158 



37-40 Kesidual strains often cause fracture long after cooling; changes of form; extreme 



slowness with which molecular equilibrium is attained, 158, 159 



41 Practical conclusion as to new and old guns, 159 



42 M. Savart's researches ; axes of greatest and least elasticity, 159 



43 Abnormal strains introduced by the consolidation of one portion of a casting before 



another; example; eifects, 159 



44, 45 Effects upon castings for large mortars and heavy guns, 160, 161 



46, 47 Eeference to Plate III. ; nature of the production of internal cavities ; various 



examples ; law of their production, direction, magnitude, 162 



CHAPTER VI Effects of Bulk and Fluid Peessuhe. 



48 Molecular condition of small parts cast on to great castings 162 



49 Apparent anomaly ; explanation, 163 



50 Practical conclusions as to the best rate of cooling castings; prevalent error as to 



this, 163 



51 Time required for great castings to cool, 164 



52,53 Cooling must be uniform; methods of hastening it; evils of unequal cooling, . . 164 



54 Effects of vertical castings; value of increased "head of metal," 164 



55 The author's experiments; Table I.; increase of density in castings of large size, 



due to their solidification under a head of metal, varying from one to fourteen 



feet in depth, 165 



56 Table II. ; decrease of specific gravity, due to increase of bulk only, 165 



57 Practical deductions, 166 



CHAPTER VII.— QnALiTY of Metal, 



58 Fallacious opinions as to the relative values of foreign and British makes of iron 



for ordnance, 166 



59 Quality of cast-iron fitted for ordnance; in Great Britain how injudiciously 



attempted to be obtained, 167 



60 Karsten's statements as to required quality of metal, and how obtained in Swe- 



den, 167 



61 Kulmann's authority in corroboration, 168 



62 Use of charcoal or pit-coal; sulphur, its elimination, 168 



63 Cold or hot blast, 168 



64 Commercial conditions which cause pig-iron fit for gun-founding not to exist in 



British markets; capable of immediate production, if demand arise, at the 

 necessary price, 169 



65 Mistake as to the general superiority of foreign over British makes of iron; Hun- 



garian cold-blast charcoal irons; Table, 169 



66 Foreign and British wrought-irons compared, 169 



67 Abortive attempts to improve quality of cast-iron by alloy vfith other metals, . . 170 



68 Stirling's patent toughened cast-iron, 170 



69 Comparative advantages of melting by cupola or by air furnace; high temperature 



of the former injures the quality of cast-iron by inducing its alloy with the 

 alkaline and earthy metals, and by developing the uncombined graphite in the 

 largest crystals ; true cause of the inferiority of hot-blast iron, 171 



