30 SCIENTIFIC AMUSEMENTS. 



when placed in a freezing mixture) becomes pasty, owing to the 

 separation in the solid form of the latter constituent, termed 

 stearine. By pressing the pasty mass \A several folds of blotting 

 paper the fluid part, oleine, is absorbed by the paper and the stearine 

 is obtained in the solid form, not melting at the ordinary tem- 

 perature if sufficiently free from the oleine. This operation is 

 best performed by means of a copying-press in a cold room, so as 

 not to thaw again the solidified portion before the liquid part is 

 separated. 



This experiment affords an illustration of a kind of process 

 largely employed in certain manufactures where solid matters 

 analogous to stearine are thus separated by cold and pressure from 

 more fluid impurities naturally accompanying them ; such methods 

 are chiefly used in the arts for preparing hard fatty matters for 

 candle-making from soft oils, &c., for obtaining paraffin wax from 

 petroleum and shale oils, spermaceti from sperm oil, and a variety 

 of similar operations. To produce the cold requisite in such cases 

 powerful freezing-machines are used, in most of which ether or 

 some still more volatile fluid is made to evaporate very quickly, 

 the evaporated liquid being recovered and used over and over 

 again. The production of cold in such cases is primarily due to 

 the fact that when a liquid evaporates, heat disappears or becomes 

 latent (vide Chapter XXL). 



Expt. 27. To Freeze out Pure Ice from Sea-Water. If 

 common salt be dissolved in water (as in sea-water), a greater 

 degree of cold will be required before the water will freeze than 

 with pure water ; but the ice which forms contains a much less 

 proportion of salt than the original brine, especially if the salt 

 water be agitated whilst freezing, so as to form small particles of 

 ice instead of a solid block, as the former can be readily drained 

 from the as yet unfrozen brine, whilst the latter is apt to enclose 

 drops of strong brine here and there throughout the mass. When 

 a quarter or a third of the water has frozen, the ice so formed 

 should be drained on a cloth from the brine ; on melting the ice 

 the water will often be found to be sufficiently free from salt to 

 be drinkable ; but if still somewhat brackish, it may be further 

 purified by repeating the process. In this way fresh water for 

 cooking purposes and for drinking may be prepared in cold 

 climates from water too salt to be otherwise used. 



It is evident that the unfrozen part of the water will be richer 

 in salt than the original brine, so that a concentration of the 

 liquor may be effected by freezing out some of the water, thus 

 producing the same result as if the brine had been strengthened 

 by boiling off part of the water. In the manufacture of salt from 



