involved in the Construction of Artillery. 361 



The American experiments, upon the possible improving effects of keeping the metal 

 for a longer or a shorter time in fusion in the furnace, although too few and inconclusive 

 as to condition, to infer much from in any vfay, are only an analogous case. The longer the 

 metal remains in the furnace, exposed to contact, at a high temperature, with many foreign 

 materials (the fuel, the flux, and the furnace itself), all highly heated, the greater will be 

 the dose of alkaline and earthy metals it will have taken up by cementation, and become 

 alloyed with — although possibly, at the same time, a certain amount of approach towards 

 mottled iron may have occurred ; and hence, in that respect, some improvement. But, that 

 the general effect is one of deterioration, is well known to practical gun-founders, wherever 

 the guns are run directly from the blast furnace, who are well aware, by long experience, that 

 the metal tapped from vei'y near, but not quite at, the top of the iluid mass in the furnace, 

 and which they call " the cream" (Rahm), produces the best gun castings. Now, this is 

 just the portion of metal, of the whole that the furnace contains, that has been the least ex- 

 posed to the deteriorating influence, of continuing in fusion, and is almost that which has 

 been the shortest time melted. 



Note H.— (Sect. 29.) 



Zinc, as found purest in commerce, and cast in the ordinary way, is malleable and laminable, 

 within a range of temperature of about from 200° to 350° Fahr. If this range be extended 

 by the change in molecular arrangement due to the circumstances alluded to in the text, 

 analogy would induce the expectation, that the range of extensibility to tensile and com- 

 pressive forces, in cast-iron, would be likewise extended by similar treatment, viz., by 

 " pouring" at the lowest possible temperature. 



Note H, bis. — (Sect. 59.) 



It is worthy of remark, that in the case of the burst Cavalli gun at Woolwich (Proof 

 Department) which was cast at Aker in Sweden, the fracture presents a coarse, granitic, 

 and soft aspect, indicative of a weak quality of metal, little better than that of the split 

 Baltic mortars. It is obvious, therefore, that neither "cold blast," nor the absence of coal 

 fuel, will alone insure proper metal for guns. 



The conditions of physical structure in cast-iron, developed in the fourth and fifth 

 chapters, derive an unconscious confirmation from a remark made, with much accuracy 

 of observation, by Mr. Edwin Clarke (" Description of Britannia Bridge," vol. i. p. 380), in 

 which he states that the central crystals, in a large mass of cast-iron, are larger than those 

 nearer the surface, which he, however, attributes to a not very clearly made-out effect of the 

 prior consolidation of the exterior of the casting. In alluding, further on, to Lieut-, now 



