Viscous Traction of Lead and Tin Alloys, 195 



component should behave independently in the mixture, 

 contributing its own share to the total observed effect. 



A considerable amount of work has been done on this 

 range of alloys, from the cryoscopic point of view. Roberts- 

 Austen ('Engineering,' 1897, lxiii. p. 233), in determination 

 of the freezing-points of lead-tin solutions, obtained an eutectic 

 point at 180°, corresponding with 32 per cent. lead. This 

 eutectic point would fall at a concentration of 4 Sn 1 Pb, or 

 Sn 4 Pb. In various communications Heycock and Neville 

 (Trans. Chem. Soc. 1892, lxi. p. 904 ; Phil. Trans. A. xcvii. 

 p. 25, Ixxi. pp. 384 & 892) showed that tin may attain 

 varying degrees of molecular complexity in different solutions, 

 thus Sn 4 in lead, Sn in zinc and bismuth, Sn 2 in silver, 

 whereas lead is monatomic in tin, cadmium, and copper, and 

 very slightly associated in silver and zinc solutions. 



The alloys used in this work were made up of approxi- 

 mately definite percentage composition, and drawn by the 

 London Electric Wire Company. They were of 1 mm. 

 diameter, and usually a length of from 70-80 cms. was used. 

 The wire, enclosed in folds of paper, was suspended from a 

 pair of wooden jaws, screwed tightly together. This method 

 almost entirely obviated slipping at the suspension. To check 

 any error from this cause an index affixed to the wire quite 

 close to the jaws was observed through a vernier microscope 

 reading to *001 cm. Any slip would thus be detected, 

 determined, and corrected for in the calculations. A similar 

 pair of jaws was screwed on to the lower end of the wire, 

 and served to carry the stressing load. Near the bottom end 

 of the wire, at an accurately determined initial position, was 

 affixed an index mark on mica, and this also was followed by 

 a vernier microscope during the time of flow. The actual 

 flow in cms., corrected for slip, was plotted against time in 

 minutes, and the data for calculation were taken off the curves 

 when a steady rate had set in. As a rule the same loads 

 (about 500 grams) were used throughout the experiments, 

 for it was found that the rate of flow was affected very con- 

 siderably by increase in the tractive force, so much so that 

 the viscosity coefficient cannot be taken as constant, but must 

 be accepted as a function of that force. The experiments 

 have been carried out at the laboratory temperature (varying 

 at different times between 10° and 22°), and there is un- 

 doubtedly a marked temperature coefficient to be introduced. 

 Further experiments are now in progress, with a view of 

 following quantitatively these two factors. 



