354 



SCIENTIFIC RECREATIONS. 



is derived from the calcareous formations, and contains lime, like the Kent 

 water. This can be ascertained by noticing the incrustations of the vessels 

 wherein the water is boiled. But water rising from hard rocks, such as 

 granite, can do little to disintegrate them at the moment, and therefore the 

 water rises purer. Springs from a great depth are warm, and are known as 

 "thermal springs"; and when they come in contact with carbonic acid and 

 some salts in their passage to the surface, they are known as "mineral waters." 

 These waters hold in solution salts of lime and magnesia, or carbonates of 

 soda with those of lime and magnesia; salts of iron, and compounds of 

 iodine and bromine are found in the natural mineral waters also, as well as 

 sulphurous impregnations, instances of which will occur to every reader. 



Fig. 342. Experiment with hydrogen. 



Fig. 343.~-The composition of water. 



We mentioned the Eudiometer just now, and we give an illustration of 

 it. This instrument is used to ascertain the proportions in which the 

 elements of water are composed by synthesis^ or a putting together of the 

 constituents of a body to make it up. This is distinguished from analysis, 

 which means separating the compound body into its elements, as we do 

 when we pass the electric current through water. 



The Eudiometer consists of a stout glass tube sealed hermetically at 

 one end ; two platinum wires are pushed in through the glass just before 

 the end is sealed. The tube is now filled with mercury, and inverted in a 

 bowl of the same metal. Hydrogen, and then oxygen, are admitted through 

 the mercury in the recognised proportions of two to one. By the time the 

 mercury is somewhat more than half displaced, the tube should be held 



