462 Intelligence and Miscellaneous Articles. 



ON THE MELTING OP LEADEN PROJECTILES BY THEIR IMPACT 

 UPON AN IRON PLATE. BY EDUARD HAGENBACH. 



At the commencement of the present year experiments were made 

 at Basle with the view of using targets of iron instead of wood in 

 practice with firearms. Strong plates of iron were, on this oc- 

 casion, fired at from the short distance of 100 paces. Conical 

 bullets by their impact against the iron plate produced a scarcely 

 perceptible indentation, and fell down near the target ; at the same 

 time the lead projectile was melted to a very considerable extent. 

 This could be recognized by the fact that, around the point where the 

 ball had struck, the plate was spattered with lead in the form of 

 a white star, that, moreover, the melted lead was found in the vici- 

 nity, and that, of the original bullet, which weighed 40 grammes, 

 only the comparatively small portion of 13 grammes remained. This 

 residual part exhibited a very peculiar kind of deformation and inver- 

 sion, as may be seen in figs. 1 and 2. Fig. 1 gives the section of 



Fig. 1. Fig. 2. 



& e, 



a> d 



the original projectile, and fig. 2 the section of the residue ; the con- 

 cave surface abed, in consequence of the pressure resulting from 

 the impact, was transformed into the convex surface a ( b t c t d r The 

 phenomenon in question is obviously interesting with regard to the 

 mechanical theory of heat, inasmuch as we have here a very distinct 

 example of the transformation of the impetus of the motion of a body 

 into the impetus of molecular motion. We will inquire how far, 

 with the help of this theory, we are in a position to account for the 

 matter in question. 



According to the statement of a competent military man, the ve- 

 locity of the projectile, under the circumstances in question, may be 



9 



VYlv 



assumed to be equal to 320 metres ; hence the impetus, — ■, of the 



movement of the body is equal to 209 kilogrammetres*. Assuming 

 424 kilogrammetres as the mechanical equivalent of the heat, this gives 

 us 0*49 thermal unit. Let us now inquire how much heat is neces- 

 sary to produce the melting described. The entire projectile (40 

 grammes) had to be raised to the temperature of the melting-point of 

 lead, or near it ; and then 27 grammes had to be melted. Assuming 

 100° for the initial temperature of the projectile, which must have been 

 somewhat warmed by the heat of combustion of the powder and by 

 * In this we neglect (what must in any case be very small) the impetus 

 due to the velocity of rotation of the projectile. 



