﻿Dr. T. J. Baker on Breath Figures. 757 



start motion. This was not true sliding, hut consisted of 

 je.ky movements accompanied l)y a gritty sound resembling 

 that produced by a diamond when drawn across glass. One 

 half of the glass surface was then rubbed with clean linen 

 and the watch-glass was placed upon it ; and it was found 

 that a pull of 4 grams was sufficient to cause steady sliding 

 without noise. Evidently the linen had contaminated the 

 glass. 



A blowpipe-flame (coal-gas) was now swept across that 

 half of the sheet which had been rubbed with linen, and 

 once across the unrubbed and therefore chemically clean 

 half. Each o£ these flame tracks was tested with the watch- 

 glass, and a pull of 5* 5 grams was required in each instance 

 to cause movement, and this motion was not smooth. 



It appears reasonable to suppose that in one case the flame 

 had removed the film of contamination left by the linen, and 

 that in the other it had slightly contaminated the half which 

 was chemically clean. 



In another experiment the flame of pure carbon monoxide 

 was used instead of a coal-gas flame, in order to eliminate 

 the possibility of contaminating the glass by the products of 

 combustion of coal-gas. Steady sliding of the watch-glass 

 occurred on the linen-rubbed part with a pull of 4 grams ; 

 but when the watch-glass was placed on the track of the 

 CO flame a pull of rather more than 7 grams was required, 

 and the movement was of the type associated with a clean 

 surface. This pull of 7 grams is very close to the value 

 (8 grams) require;! on chemically clean glass. If a thin 

 clean glass rod with a rounded end is drawn gently across a 

 glass sheet which has been rubbed with clean linen it slides 

 freely and noiselessly, but when it encounters a flame track 

 the increased friction is easily felt, and a faint squeak may 

 be heard. 



Chemical deposition of silver on a flame track. 



I£ a film of silver is deposited chemically on a sheet of 

 "cleaned" glass across which a flame of carbon monoxide 

 has been swept, it is seen that the mirror is whiter and freer 

 from pin-holes on the flamed part than it is elsewhere. This 

 points to the greater cleanliness of the flamed portion. 



A test-tube was washed out with soapy water followed by 

 tap-water, and was then thoroughly dried by rubbing the 

 inside with clean linen. A narrow belt of the tube near its 

 middle was then heated externally in a small Bunsen flame 

 to a temperature which was much below its softening-point. 



