79 
in air/’ (8) “ On evaporation/’ and (4) '' On the expansion of 
gases by heat.”^' 
No. 8 is an apparatus used for the determination of the 
tension of volatile liquids at low temperatures ; it consists 
of a siphon tube, at the upper end of which is a scale in 
inches in Dalton’s handwriting. He describes it thus : 
I took a barometer tube 45 inches in length, and having 
sealed it hermetically at one end, bent it into a siphon 
shape, making the legs parallel, the end that was closed 
being 9 inches long, the other 86 inches. I then conveyed 
2 or 8 drops of ether to the end of the closed leg and filled 
the rest of the tube with mercury except about 10 inches 
at the open end. This done, I immersed the whole of the 
short leg containing the ether into a tall glass containing 
hot water.” 
No. 9 is a smaller tube containing another liquid, also 
having a graduated scale written on paper and attached to 
the tube. Nos. 10, 11, 12, 18, 14, are tubes used by 
Dalton for measuring the tension of vapour from water and 
other liquids at higher temperatures than their boiling 
points, both in a vacuum and air. No. 15 is a tube used by 
Dalton for measuring the tension of the vapour of bisulphide 
of carbon, labelled “ Sulphuret carb.,” with a paper scale in 
Dalton’s handwriting, and a cork showing that the upper 
portion of the tube containing the bisulphide of carbon 
could be heated in a water bath to various temperatures. 
No. 16 is a manometer tube, fixed into a board, divided and 
numbered by Dalton. No. 17 is an apparatus used by 
Dalton for the determination of the tension of the vapour 
of ether, and is interesting as being the instrument by means 
of which Dalton arrived at one of his most important 
experimental laws. It is described as follows (p. 564): — 
* Experimental essays on tlie above subjects, by John Dalton, read 
October 2nd, 16tb, and 30th, 1801, and published in the 1st series, vol. 5, 
part 2, of the Memoirs of the Literary and Philosophical Society of Man- 
chester. 
