47 



perature gradually raised to about 88° Fahr., the surface of the 

 demarcation between the liquid and the gas becomes fainter, loses 

 its curvature, and at last disappears. The space is then occupied 

 by a homogeneous fluid, which exhibits, when the pressure is either 

 suddenly diminished or the temperature slightly lowered, a peculiar 

 appearance of moving or flickering strise thoughout its entire mass. 



At temperatures above 88° no liquefaction of carbonic acid or 

 separation into two distinct forms of matter can be affected, even 

 when a pressure of 250 to 300 atmospheres is applied. 



Dr. Andrews then proceeded to describe his recent investigations, 

 which form the subject of the Bakerian Lecture of 1869, and will 

 be published in the Philosophical Transactions of the Royal Society 

 of London. After stating the experimental results, he proceeded : — 

 " We are now prepared for the consideration of the following im- 

 portant question — what is the condition of carbonic acid when it 

 passes at temperatures above 88° from the gaseous state down to 

 the volume of the liquid, without giving evidence at any part of 

 the process of liquefaction having occurred ? 



" Does it continue in the gaseous state, or does it liquify? or 

 have we to deal with a new condition of matter ? 



" The answer to this question, according to the results of the 

 experiments, is to be found in the close and intimate relations 

 which subsist between the gaseous and liquid states of matter. 

 The ordinary gaseous and ordinary liquid states are, in short, only 

 widely separated forms of the same condition of matter, and may 

 be made to pass into one another by a series of gradations so 

 gentle that the passage presents nowhere any interruption or 

 breach of continuity. 



" From carbonic acid as a perfect gas to carbonic acid as a per- 

 fect liquid, the transition may be accomplished by a continuous 

 process, and the gas and liquid are only distant stages of a long 

 series of continuous physical changes. These properties are not 

 peculiar to carbonic acid, but are true of all bodies which can be 

 obtained as gases and liquids. Nitrous oxide, hydrochloric acid, 

 ammonia, sulphuric ether, and sulphuret of carbon, all exhibit 

 critical points of temperature, beyond which pressure alone is in- 



