i 



TRANSACTIONS OF SECTION B. '699 



The second part of tlie paper deals with tlie effects of moderate temperatures 

 (up to 200° 0.) on such metals as lead, zinc, tin, and cadmium. The authors have 

 found that when these metals are subjected to a very severe plastic strain the 

 original large crystals are broken up into much smaller ones, without, however, 

 destroying their truly crystalline nature. They have further found that when so 

 treated these metals readily recrystallise. In' the case of severely strained lead 

 they have shown that even at the ordinary temperature of a room gradual recrys- 

 tallisation can be observed in the course of several months, while at higher tem- 

 peratures the changes are much more rapid. A freshly strained specimen exposed 

 to 200° C. was found to recrystallise in a few minutes. It was also found that 

 severe plastic strain is essential to such recrystallisation, and that minute crystals 

 obtamed by chilling the metal in casting are not capable of recrystallisation at 

 such moderate temperatures. Closer observation has shown that this recrystallisa- 

 tion of strained metal takes place by the growth of certain of the minute crystals 

 at the expense of their neighbours; individual crystals have been observed to 

 grow until they were many hundreds of times larger than their neighbours. 



The final section of the paper deals with a theory which one "of the authors 

 (W. Rosenbain) has advanced as an explanation of these phenomena of annealing. 

 According to this view, which both authors believe to be correct, the metallic im- 

 purities present in the metal, and forming with it eutectic alloys, play an essential 

 part m these actions. In the ordinary crystallisation of the metal these eutectics 

 form thin films of intercryjtalline cement, and, according to the theory of the 

 authors,_ the growth of one crystal at the expense of its neighbour occurs by means 

 of solution in and diffusion through the eutectic films of the metal constituting the 

 crystals. Evidence is adduced to show that such ditiusion would be greater in one 

 direction than the other, and to support the authors' belief that the action may be 

 electrolytic. As a consequence of this theory the authors were led to make 

 experiments on the cold welding of lead, and they have found that, as the theory 

 would indicate, a weld between clean surfaces of lead is a barrier to crystalline 

 growth, but that such growth readily crosses a weld into which a small amount of 

 a suitable metallic impurity had been introduced. The authors believe that these 

 experiments strongly support their ' solution theory ' of annealing. 



6. 071 the Electric Conductivitij of the Alloys of Iron. 

 By Professor W. F. JBarrett, F.E.S. 



7. Some neio Chemical Compounds discovered hy the Use of the 

 Electric Furnace. By C. S. Bradley. 



These chemical compounds, which were discovered and examined by ]\Ir. Charles 

 "B. Jacobs, of New York, consist of the alkaline earth silicides of calcium, barium, 

 or strontium ; by a secondary step silico-acetylene is obtained. 



They have the formula CaSi.,, BaSi,,, and SrSi., respectively, and are the silicon 

 analogues of the alkaline earth carbides, while the silico-acetylene is the analogue 

 of acetylene having the formula Si,II., when the carbonates or oxides of the 

 alkaline earths are mixed with silica in the form of ground quartz or sand, in 

 which the relative atomic proportion of the alkaline earth metal to the silicon in 

 the mixture is asl is to 2, and sufficient carbon to effect the reduction is added, or, 

 when silicates of the alkaline earth metals in which the atomic relation of the 

 earth metal to the silicon is as 1 to 2, are mixed with sufficient carbon to take up 

 the oxygen of the compounds present, and heated in the electric furnace under 

 conditions substantially like those maintained in the manufacture of alkaline earth 

 carbides, silicides of the alkaline earth metals result. 



As an example of the process the following reactions for the formation of 

 barium silicide from the barium compounds are given : 



(1) BaCO, + 2 SiO., + GC = BaSi,, + 7 CO 



(2) BaO + 2 SiO^ + 60 = BaSio + 5 CO 



