112 CONDENSATION OF WATER 



the zero of our thermometric scale. The well-known 

 pungent compound, ammonia, so exceedingly volatile at 

 common temperatures, is converted into a crystalline, 

 translucent, white substance at the temperature of 

 103. The difficulties which necessarily attend the 

 exposure of a body to extreme cold and great pressure 

 at the same time, appear to be the only obstacle to the 

 condensation of oxygen, hydrogen, and nitrogen gases. 

 A sufficient amount of condensation was, however, 

 effected by Dr. Faraday, to lead him to the conclusion, 

 arrived at also by other evidences, that hydrogen, the 

 lightest of the ponderable bodies, partakes of the nature 

 of a metal.* 



During the solidification of water by freezing, some 

 remarkable facts may be noticed. 



Water, in cooling, gradually condenses in volume 

 until it arrives at 40 Fahr., which appears to be the 

 point of greatest density. From this temperature to 

 that of 32, the point at which it begins to solidify, its 

 volume remains unchanged,* as crystallisation (freezing) 

 begins, the bulk increases, the mass becomes specifically 

 lighter, and it swims on the surface of the fluid. From 

 40 to 32 the particles of water must be taking up 

 that new position which is essential to the formation of 

 the solid ice; and while this is taking place, every 

 substance held in solution by the water is rejected. 



If we mix with water the deepest colouring matter 

 the strongest acid or the most acrid poison they are 

 each and all rejected during the process of freezing, and 

 if the water has been kept in a state of agitation during 

 the process so that the liberated particles may not be 

 mechanically entangled the ice will be transparent, 

 colourless, tasteless, and inert the substances rejected 

 being gathered together in the centre of the frozen mass 



* On the Liquefaction and Solidification of Bodies generally 

 existing as Gases, by Michael Faraday, D.C.L.,F.R.$., &c.; Philo- 

 sophical Transactions, vol. cxxxvi, p. 155. 



