806 Mr, F. B. Young on the 



C. General Phenomena. 



A brief statement is given of the general phenomena 

 observed in tube XIV. in the neighbourhood of the critical 

 temperature. 



(1) If the tube was slowly cooled after being maintained 

 at a temperature about 3° C. above 6 C : — 



(a) A faint opalescent haze appeared throughout the tube 

 and gradually became denser, at first very slowly, but 

 more rapidly as the temperature 6 C was approached. 

 Just above that temperature a dense opaque fog 

 pervaded the tube and the substance appeared greatly 

 agitated. 



(b) At 6 C a faint, flat meniscus was perceived slowly rising 

 around the plunger B (fig. 2). A brisk ebullition of 

 fine bubbles was generally discernible through the 

 dense opalescence which still persisted after the 

 appearance of the meniscus. 



(c) As the temperature was further reduced the opalescence 

 became fainter and at length disappeared. The ebul- 

 lition became more marked, while condensation was 

 apparent in the vapour. The meniscus gradually rose, 

 becoming at the same time clearer and assuming a 

 concave shape. (If the reduction of temperature was 

 effected in sudden drops of about 0°'02 the tube 

 became filled each time with an oily cloud which 

 dissolved into a rain of bubbles and drops rising and 

 falling respectively into the meniscus.) 



These appearances may be regarded as belonging to con- 

 ditions of equilibrium, since by arresting the fall of tempe- 

 rature the changes described could be arrested at any point. 



(2) If the temperature was raised extremely slowly 

 {e.g. o, 01 C. in 5 mts.) it was possible to approximate to a 

 reversal of the phenomena of slow cooling, the condensation 

 phenomena in the vapour phase excepted. It was difficult, 

 however, to avoid the effects of lag detailed in (3) and (4). 



(3) If the temperature was raised as quickly as possible to 

 the neighbourhood of C , the liquid quickly became opalescent 

 and after a few minutes the vapour also became opalescent. 

 At the same time the meniscus fell and, given sufficient time, 

 fell below the top of the plunger, beyond which point its 

 movements were difficult to follow. 



(4) If the temperature was rapidly raised a little above 

 6 C (say o, 2 C.) and then maintained constant, the meniscus 

 quickly became indefinite in outline and nebulous in appear- 

 ance ; it assumed at the same time a slightly convex 



