involved in (he Construction of Artillery. 155 



1°. The high temperature of the fluid iron above that just necessary 

 to its fusion, which influences — 



2°. The time that the molten mass takes to cool down and assume again 

 the solid state. 

 29. These laws have very recently received the most striking confirmation 

 from some quite analogous researches "Upon the Molecular Properties of Zinc," 

 made by Mons. P. W. BoUey, and published in the "Annalen der Chim. und 

 Pharm." st. scv. p. 294. Zinc and iron are bodies so closely allied in all their 

 properties, chemical and physical, that in almost everything that relates to 

 the latter, analogy holds in the most striking manner, and this proves to be 

 so here, — where M. Bolley's results, arrived at, in all probability, without even 

 a knowledge of the facts above adverted to as aflecting cast-iron, are found per- 

 fectly in parallel. 



His paper scarcely admits of extracts: it will sufiice, however, to state his 

 chief results. He finds that zinc, of whatever sort, whether chemically pure, 

 or alloyed with various minute foreign metals, as found in commerce (just like 

 cast-iron), is capable of crystallizing upon cooling from fusion in two distinct 

 forms. In one, the fracture presents a small-grained, uniform, confusedly crys- 

 talline surface, it is " grenue." In the other, large, well-formed lamellar crys- 

 tals, with their principal axes, standing perpendicular to the bounding surfaces 

 of the cooled mass, well known to all who have seen a commercial ingot of zinc 

 broken, are produced. 



He proceeds to investigate the conditions under which these two states of 

 aggregation occur, and he finds they have nothing to do with the purity of 

 the zinc (as respects extraneous alloying metals, or even the carbon that it 

 contains, always more or less of), nor with the sort of original crystalline ag- 

 gregation of the zinc used for experiment, i. e. whether in large or small crys- 

 tals ; but that it depends upon the higher or lower temperature at which the 

 zinc is fused and poured into the mould, and upon the rate at which it is cooled 

 down to solidification. 



Thus, if zinc be heated just to its fusing point (773° Fahr.), and no higher, 

 and be then cast in the mould — 



Its crystalline grain on fracture is (grenue) small, fine, and confusedly 

 crystallized. 



Its specific gravity is as great as 7-18. 



