44 THE BEGINNINGS OF LIFE. 



differences exist as to the amount of heat which is 

 necessary for converting them into the one or the other 

 state. In short, the particular temperatures at which 

 different elementary or compound substances are capa- 

 ble of existing respectively as solids, fluids, or vapours, 

 varies ad infnitum, in accordance with differences in 

 the molecular nature and properties of the bodies 

 themselves. Most of their distinctive chemical charac- 

 ters remain, however, essentially the same, in whatever 

 physical condition the matter may at the time exist 

 whether that of gas, fluid, or solid 1 . 



When reduced to the state of solution, also, bodies 

 lose the obvious physical characters which originally 

 distinguished them, Their individual and separate 

 existence has gone their constituent molecules have 

 parted company, and are, for the time, more intimately 

 related to the molecules of the solvent. The solvent 

 itself may vary much in nature, though that with 



1 The molecular relationships of liquids and their vapours has been 

 further elucidated in a recent memoir by Prof. Tyndall, ' On the Action 

 of Rays of high Refrangibility upon Gaseous Matter,' in which he makes 

 the following highly interesting statements : ' i. The vaporous nitrite 

 of amyl absorbs with such avidity the rays competent to decompose it that 

 a very small depth of the vapour quenches the efficient rays of a power- 

 ful beam of solar or electric light. 2. The vaporous iodide of allyl, on 

 the contrary, permits a beam to traverse it for long distances without very 

 powerfully diminishing the chemical power of the beam. 3. The liquid 

 nitrite of aniyl, in a stratum one quarter of an inch thick, quenches all the 

 rays which could act chemically upon its vapour. 4. The liquid iodide 

 of allyl, on the contrary, in a stratum of four times the thickness just 

 mentioned, does not materially diminish the power of the beam to act 

 upon its vapour.' (* Phil. Trans.' 1870, p. 344.) 



