700 



SOLID BODIES. 



SORGHUM. 



SOLID BODIES, THE FLOW OF. M. Tresca 

 has devoted much attention to this interesting 

 subject, and recently laid the results of his in- 

 vestigations before the " Society of Civil Engi- 

 neers in France." His experiments were con- 

 ducted with the ordinary metals, lead, tin, 

 copper, iron, and others, and the whole process 

 may be described as liquefying the substances 

 by pressure, and observing their behavior when 

 issuing in jets from a small orifice. A strong 

 cylinder having a small round hole at the bot- 

 tom, was filled with the metal in its natural 

 cold state (excepting iron and other peculiarly 

 refractory metals), and a sufficiently powerful 

 pressure applied at the upper extremity 

 Avhereupon the metal issued from the orifice in 

 a jet like that of a liquid. Iron and other re- 

 fractory metals it was necessary to heat to a 

 certain point not the melting point before 

 the same results could be obtained with facil- 

 ity. M. Tresca observes that the flow of solid 

 bodies offers advantages for observing the vena 

 contracts, and the laws regulating phenomena 

 of this nature better than the flow of liquid 

 bodies. The molecules under the pressure to 

 which they are subjected assume, if not a true 

 liquid form, at least a condition of extreme 

 divisibility closely approaching thereto. In the 

 cylinder alluded to, a mass of lead exactly fit- 

 ting its internal diameter was forced in a jet 

 through the orifice. No particulars with re- 

 gard to the motion or arrangement of the mole- 

 cules could be observed in this jet; but, on re- 

 peating the operation with the substitution of 

 a number of thin disks of lead, in place of one 

 solid mass, the following remarkable results 

 were noted. By cutting the jet transversely, it 

 was observed, after a little time, that a portion 

 of all the disks issued simultaneously from the 

 orifice in the shape of c6ncentric tubes, or hol- 

 low pipes, one inside of the other : the lower 

 disks formed the external tubes, and the upper 

 disks the internal tubes; the behavior of the 

 flow being precisely similar to that of water, 

 passing through the orifice of a cylinder, the 

 upper strata of the fluid supplying the internal 

 particles of the jet, and the lower strata the ex- 

 ternal ones. With twenty disks of lead, having 

 a diameter of 3.9 inches, and an aggregate 

 thickness of 2.35 inches, a jet was obtained 

 23.4 inches long, the diameter of the orifice 

 being from .786 to 1.96 inches. The contents 

 of the unbroken jet issuing from an orifice of 

 0.786 inches in diameter were rather more 

 than one-third the whole mass of the metal in 

 the cylinder. With a larger hole, the whole 

 contents would have been voided in a single jet. 

 With smaller orifices the jets were proportion- 

 ately longer, but retained the same character- 

 istics. Other metals acted upon furnished sim- 

 ilar results, and by exercising great precautions, 

 the external and internal tubes could be sep- 

 arated from each other. Small waxen tablets 

 under the same conditions behaved in exactly a 

 similar manner. 

 A mass of metal in a mould may be imagined 



to consist of two concentric cylinders, one cor- 

 responding to the orifice of the flow, and the 

 other enclosing it. When pressure is given to 

 the upper surface, the whole exterior cylinder 

 becomes compressed, and gives ri:je to the flow 

 by driving out the central portion by a uniform 

 pressure all around it. In fact, the flow takes 

 place more strictly in accordance with the law 

 of concentricity of layers than that of parallel- 

 ism of sections. 



The crushing of solid bodies is attended with 

 phenomena analogous to those above described. 

 When a block of tin composed of several disks 

 is subjected to a crushing force, a progression 

 of particles from the centre to the circumference 

 occurs, and the disks take the shape of lenses 

 grouped uniformly around the axis of a cylin- 

 der. Other metals, such as lead, and the sub- 

 stance wax, behave similarly. Again, it is 

 known that in. crushing a mass of metal con- 

 sisting of concentric cylinders a bulging takes 

 place at about the middle of the height. The 

 sides of the exterior cylinders deflect, but still 

 preserve their continuity. If we suppose a cyl- 

 inder of lead to be made up of concentric tubes, 

 the lengthening of either the external or in- 

 ternal tubes can be produced at pleasure, ac- 

 cordingly as heavy or light blows are struck 

 upon it. The shock of a heavy blow will be 

 transmitted to the central tubes, while that of 

 a light blow will be wholly expended on the 

 exterior tubes. A knowledge of these facts is 

 of practical value in the stamping of metals. 



SORGHUM. The sorts of cane indigenous 

 to China, as perhaps also to parts of the East 

 Indies, and to Southern Africa, which thrive 

 and perfect their juices and seed in higher lati- 

 tudes than does that long and specially known 

 as the u sugar-cane," belong to the family of 

 grasses, and more specifically to the millets. 

 Not only the Chinese cane (sorghum sacchara- 

 tum ; Fr., sorgho sucre ; Ital., sorgo\ and the 

 African cane, or imphee, but also the dourah 

 corn and the broom-corn, are now accepted as 

 but varieties of a single primitive species, some- 

 times referred to Holcus,' and sometimes to 

 Andropogon (being, iu this view, the A. sor- 

 ghum) ; or, indeed, by some writers, as consti- 

 tuting a distinct genus, on which hypothesis 

 the sugar-bearing millets form the species, 

 sorghum vulgare. Thus, the generic term 

 " sorghum " embracing all the varieties, theso 

 may then, in common language, be properly 

 distinguished according to their source under 

 the names of "sorgho" and "imphee." The 

 history of the introduction of these plants into 

 Europe and this country is already generally 

 known. 



Mr. William Clough, of Cincinnati, states 

 that the several sub- varieties of imphee, origi- 

 nally described by Mr. Wray under the native 

 titles, have, in this country, already become so 

 far modified and assimilated in their characters 

 that but five or six distinct sorts can now bo 

 traced ; while, except in the case of the Boom- 

 see-a-na and the Nee~a-za-na, there is scarcely 



