52 PRINCIPLES OF CHEMISTRY 



this time of the year the ice splits up into spars or prisms, bounded by 

 angles proper to substances crystallising in the hexagonal system. The 

 temperatures at which water passes from one state to another are 

 taken as fixed points on the thermometer scale : namely, the zero 

 corresponds with the temperature of melting ice, and the temperature 

 of the steam disengaged from water boiling at the normal barometer 

 pressure (that is 760 millimetres measured at 0, at the latitude of 45, 

 at the sea level) is taken as 100 of the Celsius scale. Thus, the fact 

 that water liquefies at and boils at 100 is taken as one of its 

 properties as a definite chemical compound. The weight of one cubic 

 metre of water at 4 is 1,000 kilos, at it is 999'8 kilos. The weight 

 of a cubic metre of ice at is less namely, 917 kilos ; the weight of a 

 cubic metre of water vapour at 760 mm. pressure and 100 is only 0'60 

 kilos ; the density of the vapour compared with air =; 0'62. and com- 

 pared with hydrogen = 9. 



These data briefly enumerate the physical properties of water as a 

 separate substance. As a supplement to this it may be added that water 

 is a mobile liquid, colourless, transparent, without taste or smell, c. 

 It is unnecessary to dwell on these properties here, as water is familiar 

 to all ; other properties will also be pointed out in describing less known 

 substances. Its latent heat of vaporisation is 534 units, of liquefac- 

 tion 79 units of heat. 11 The large amount of heat stored up in water 



11 Of all known liquids, water exhibits the greatest cohesion of particles. Indeed, it 

 ascends to a greater height in capillary tubes than other liquids ; for instance, two and a 

 half times as high as alcohol, nearly three times as high as ether, and to a much greater 

 height than oil of vitriol, &c. In a tube of two millimetres diameter, water at ascends 

 15 '8 millimetres, counting from the level of the liquid to two-thirds of the height of the 

 meniscus, and at 100 it rises 12'5 millimetres. The cohesion varies very uniformly with 

 the temperature ; thus at 50 the height of the capillary column equals 13'i) millimetres 

 that is, the mean between the columns at and 100. This uniformity is not destroyed 

 even on approaching the freezing point, and gives reason to think that at high tempera- 

 tures cohesion will vary as uniformly as at ordinary temperatures ; that is, the difference 

 between the columns at and 100 being 2'8 millimetres, the height of the column at 

 500 should be 15;/- (5 x 2'8) = Vji millimetres. Consequently, at these high temperatures 

 the cohesion between the particles of water would be almost nil. Only certain solutions 

 (sal ammoniac r.i-a lithium chloride), and these only with a great excess of water, rise 

 higher than pure water in capillary tubes. The great cohesion of water doubtless 

 determines many of both its physical and chemical properties. 



The quantity of heat required to raise the temperature of one part by weight of ( 

 water from to 1, i.e., by 1 C., is called the unit of heat or calorie; the specific 

 heat of liquid water at is taken as equal to ttnity. The variation of this specific 

 heat with a rise in temperature is inconsiderable in comparison with the variation 

 exhibited by the specific heats of other liquids. According to Ettinger, the specific heat 

 of water at 20 =1'016, at 50 = r039, and at 100 = 1'078. The specific heat of water is 

 greater than that of all other known liquids ; for example, the specific heat of alcohol at 

 is 0'5475 i.e., the quantity of heat which raises 55 parts of water 1 raises 100 parts 

 of alcohol 1. The specific heat of oil of turpentine at is 0'4106, of ctli.-r <f,V2<), of 

 acetic acid G'527-4, of mercury 0'038. This means that water is the best condenser or 



