356 



SCIENTIFIC RECREATIONS. 



never depart. Snowflakes are regular six-sided prisms grouped around a 

 centre forming angles of 60 and 120. There are a number of forms, as will 

 be seen from the accompanying illustrations, and at least ninety-six varieties 

 have been observed. One snowflake, apparently so like all other flakes that 

 fall, can thus be viewed with much interest, and yet, while so very various, 

 snovvflakes never get away from their proper hexagonal structure. It has been 

 remarked that snowflakes falling at the same time have generally the same 

 form. 



Of the latent heat of ice, etc., we have already spoken in our article 

 upon Heat, and therefore it will be sufficient to state that the latent heat of 

 water is 79 thermal units, because when passing from the liquid to the 

 solid state a certain amount of water absorbs sufficient heat to raise 



Fig. 346. Snow crystals. 



an equal quantity of the liquid 79. This can be proved by taking 

 a measured quantity (say a pint) of water at 79 and adding ice of the 

 same weight to the water. The mixture will be found to be at zero. 

 Therefore the ice has absorbed or rendered latent 79 of heat which the 

 water possessed. If we melt ice until only a trace of it is left, we shall still 

 find the water as cold as the ice was ; all the latent heat is employed in 

 melting the ice. So it will take as much heat to bring a pound of ice at 

 zero to a pound of water at zero, as it would to raise 79 pounds of water 

 i. The same law applies to steam. 



Water can be distilled in small quantities by an apparatus, as figured 

 in the illustration, and by these means we get rid of all impurities which are 



