1913.] NATURAL SCIENCES OF PHILADELPHIA. 583 



by the dioxide inclusions indicate that when a liquid is heated to its 

 critical point and is finally converted into a gas, it gradually passes 

 from one to the other state. A slight rise in temperature causes the 

 inclosed bubbles rapidly to diminish in size, indicating a high expansion 

 coefficient of the liquid portion. After the bubbles have disappeared, 

 a further advance of temperature does not burst the walls of the cavity, 

 showing the liquid to be compressible. In cooling, the bubble or 

 bubbles suddenly appear of a definite size instead of growing from a 

 mere point. Before that moment the contents of the cavity are 

 no doubt in a liquid condition, otherwise bubbles could not be seen. 

 By cooling the prevailing high pressure is reduced until it falls below 

 the vapor pressure of the dioxide corresponding to the temperature, 

 and there is a tendency to form a small bubble. But its formation 

 is resisted by the cohesion of the molecules. Only after the pre- 

 vailing pressure has been lowered so much that the excess of the 

 vapor pressure is competent to overcome cohesion will a sudden 

 rupture take place, attended by an instantaneous reduction of the 

 volume of the liquid due to the sudden increase of pressure. This 

 accounts for the sudden appearance of bubbles at a definite size. 

 We can therefore conclude that a liquid, when near its critical point, 

 is in a state that is intermediate between the liquid and the gaseous 

 states. 



Mr. Van Sickle described a method of making detailed labels 

 for microscopic slides by photographic reduction. 



The following was ordered to be printed: 



