CHEMICAL SCIENCE. 203 



arate the boron, the mass is plunged into boiling caustic soda, which 

 dissolves the aluminum, and is afterward treated with hydrochloric 

 acid, to remove all traces of iron, and with a mixture of nitric and 

 hydrofluoric acids, to get rid of any silicon that may have been left 

 by the soda. After all these processes have been gone through, the 

 boron remains alone. 



An examination of the boron obtained in this way shows that a 

 great analogy exists between it and carbon, which, as every one 

 knows, is found in three forms : uncrystallized in charcoal ; semi-crys- 

 tallized in plumbago ; and crystallized in the diamond. Similarly, 

 the boron resulting from the above experiment is found to exist in 

 three forms, namely, in black flakes almost as hard as the diamond; 

 in brilliant prismatic crystals, less hard than the former variety ; and 

 in small, beautifully-formed reddish crystals, having a great resem- 

 blance to the diamond. These crystals are as hard as the diamond 

 itself, and may, in the course of time, should their manufacture be 

 brought to perfection, supersede that stone in many of its uses, such 

 as cutting and polishing precious stones, forming jewels in watches, 

 etc. ; and thus, although, from their being unknown in nature, they 

 cannot be considered precious stones, the discovery of these boron 

 diamonds may prove of more practical value than all the attempts at 

 the artificial production of the real diamond. 



THE ANNEALING TEMPERATURE OF METALS. 



The " annealing temperature " has not yet been ascertained for any 

 one metal, and all that is known about it is, that there is a fixed and 

 rather narrow range of elevated temperature peculiar to each metal, 

 without the limits of which annealing does not take place, and that 

 the absolute mean temperature for each metal seems to be greater in 

 some proportion as the fusing temperature of the metal itself is higher. 

 Platina, for instance, when hard from wire-drawing or lamination, is 

 not annealed under an intense white heat ; wrought iron at about a 

 bright red, in some sorts not before a yellow heat ; copper, at a low 

 cherry-red ; and when we come down to the metals of very ready 

 fusibility, such as tin and lead, their annealing temperature appears 

 to be so low that the heat evolved in them by conversion of mechan- 

 ical force in laminating or wire-drawing is sufficient to keep them 

 annealed, that is, they cannot be hardened by such processes. It is 

 this curious fact of molecular physics which affords the explanation 

 of the circumstance, well known to those engaged in the trades of 

 rolling sheet lead, or " drawing " lead pipes by the older methods, 

 namely, that the rolling or drawing can be accomplished by a less 

 total expenditure of power if performed fast than much more slowly. 

 That is to say, the power demanded is a minimum when the pressure 

 is sufficiently sharp to evolve the heat of annealing in the lead. 

 Upon a like condition (with others not here in question) depends the 

 curious process of forcing up in pure tin the patent collapsible ves- 

 sels of Rand, now so extensively in use for receptacles of oil-colors, 

 perfumes, etc. Journal of the Franklin Institute. 



