418 Professor Sir James Deivar [Jan. 16, 



WEEKLY EVENING MEETING, 



Friday, January 16, 1903. 



Sm James Ckichton-Browne, M.D. LL.D. F.R.S., Treasurer and 

 Vice-President, in the Chair. 



Professor Sir James Dewar, M.A. LL.D. D.Sc. F.R.S. MM.L 



Low Temperature Investigations. 



In the Friday Evening Discourse delivered in the year 1896, en- 

 titled "New Researches on Liquid Air" (I'roc. Roy. Inst.), it was 

 shown that seven substances, having very dififerent coefficients of 

 expansion, viz. cadmium, lead, copper, silver, calc spar, rock crystal, 

 silver iodide, all gave the same density for liquid oxygen, when 

 used to determine the weight displacement in the liquid, provided 

 the correcting factor used in each case was the calculated mean co- 

 efficient of cubical expansion found by extending the values of Fizeau 

 to low temperatures. The fact of the uniformity in the resulting 

 oxygen density proved that the parabolic law of Fizeau may safely 

 be used for extrapolation at low temperatures as far as the boiling 

 point of air, especially in the case of the metals. 



The determination of the densities of substances at the boiling 

 point of oxygen — and hence of their mean coefficients of expansion 

 between that temperature and ordinary temperatures — opens out 

 a very large field of investigation, from which, if a sufficiently 

 large number of observations were available, valuable deduc- 

 tions might be drawn. On account, however, of the expense and 

 trouble of producing quantities of liquid oxygen, its use for this 

 purpose is not likely to become general, although, when available, it 

 is the easiest body to use in conducting such experiments, especially 

 when the vacuum vessel containing it is immersed in a larger vessel 

 containing the same fluid or well evaporated air. The ease with 

 which liquid air can now be obtained in many laboratories suggests 

 that its application to work of this kind would be a convenience. 

 The use of a mixture of varying composition and density like liquid 

 air necessitates a determination of its density with accuracy and 

 rapidity before and during the course of the experiments. For this 

 purpose, liquid air that had been allowed to evaporate for twenty-four 

 hours in advance was used in large silver-coated vacuum vessels of 

 some 3 litres capacity. In order to ascertain the density of the 



