June 5, 1896.] 



SCIENCE. 



821 



The common language of sex has alwaj^s 

 dealt in analogies. There are perfectly 

 good and sufficient technical terms to 

 designate the homologies and the ultimate 

 physiological processes. If the hypercriti- 

 cism of the plant morphologists were to be 

 accepted for the animal creation, pande- 

 monium would come of it. One could not 

 speak of the members of generation as sex 

 organs, nor of any animal as male or fe- 

 male. I insist that it is perfectly proper to 

 speak of a staminate willow as male, be- 

 cause its ultimate function is paternity ; if 

 I cannot speak of it as a male plant, then 

 I cannot call a bull a male animal. 



L. H. Bailey. 



ON THE DIFFUSION OF 3IETALS.'' 



PART I. DIFFUSION OF MOLTEN METALS. 



In the first part of the paper the author 

 alludes to some earlier experiments he made 

 in 1883 on the diffusion of gold, silver and 

 platinum in molten led. He points out that, 

 although the action of osmotic pressure in 

 lowering the freezing point of metals has 

 been carefully examined, very little atten- 

 tion has been devoted to the measurement, 

 or even to the consideration, of the molec- 

 ular movements which enable two or more 

 metals to form a truly homogeneous fluid 

 mass. The absence of direct experi- 

 ments on the diffusion of molten metals is 

 probably explained by the want of a sufli- 

 ciently accurate method. Ostwald had 

 stated, moreover, with reference to the dif- 

 fusion of salts, that " to make accurate ex- 

 periments in diffusion is one of the most dif- 

 ficult problems in practical phj^sics," and 

 the difiiculties are obviously increased when 

 molten metals diffusing into each other take 

 the place of salts diffusing into water. 



The continuation of the research was 

 mainly due to the interest Lord Kelvin had 



* Abstract of the Bakerian lecture given by Pro- 

 fessor W. C. Roberts-Austen before the Royal Society 

 and printed in the Proceedings of the Society. 



always taken in these experiments. The 

 want of a ready method for the measure- 

 ment of comparatively high temperatures, 

 which led to the abandonment of the earlier 

 work, was overcome when the author ar- 

 ranged his recording pyrometer, and the 

 use of thermo-junctions in connection with 

 this instrument rendered it possible to 

 measure and record the temperature at 

 which diffusion occurred. Thermo-junc- 

 tions were placed in three or more positions 

 in either a bath of fluid metal or an oven 

 carefully kept hotter at the top than at the 

 bottom. In the bath or oven, tubes filled 

 with lead were placed, and in this lead, 

 gold, or a rich alloy of gold, or of the metal 

 under examination, was allowed to diffuse 

 upwai'ds against gravity. The amount of 

 metal diffusing in a given time was ascer- 

 tained by allowing the lead in the tubes to 

 solidify ; the solid metal was then cut into 

 sections, and the amount of metal in the re- 

 spective sections determined by analysis. 



The movement in linear diffusion is ex- 

 pressed, in accordance with Fick's law, by 

 the differential equation 



dv (Pv 



dt dx^' 



In this equation x represents distance in 

 the direction in which diffusion takes place ; 

 V is the degree of concentration of the dif- 

 fusing metal, and t is the time ; h is the dif- 

 fusion constant, that is, the number which 

 expresses the quantity of the metal in 

 grams diffusing through unit area (1 sq. 

 cm.) in unit time (one day) when unit dif- 

 ference of concentration (in grams per c. c. ) 

 is maintained between the two sides of a 

 layer 1 cm. thick. The author's experi- 

 ments have shown that metals diifuse in one 

 another just as salts do in water, and the 

 results wei'e ultimately calculated by the aid 

 of tables prepared by Stefan for the calcula- 

 tion of Graham's experiments on the dif- 

 fusion of salts. 



The necessary precautions to be observed 



