THE REASON WHY. 171 



" He gathereth the waters of the sea together as an heap ; he layeth up the 

 depth in storehouses." PSALM xxxm. 



leaves the mineral matters behind ; they therefore form a crust 

 around the sides of the kettle. 



It is said that if a child's marble be placed in a kettle, it \pill attract the 

 earthy particles, and prevent the encrusting of the sides of the vessel. 



763. Why is it difficult to wash, in hard water ? 

 Because the soap unites with the mineral matters in the water, 



and being neutralised, thereby, cannot dissolve the dirt which we 

 desire to cleanse away. 



764. Why is the sea milt ? 



Because salt is a mineral which prevails largely in the earth, and 

 which, being very soluble in water, is taken up by the ocean. 



Lakes and rivers, also, even those that are considered fresh, hold 

 in solution some degree of saline matters, which they contribute to 

 the ocean. 



As, in the evaporations from the sea, the salt remains in it, while 

 the vapours fall as rain, and again wash the earth and carry some 

 of its mineral properties to the ocean, the greater saltncss of the 

 sea, as compared with rivers, is accounted for. 



By some persons the opinion is entertained that the sea has been 

 gradually getting salter ever since the creation of the world. This, 

 they say, arises from the evaporatiou of water free from salt, and the 

 returns of the water to the sea, taking with it salt from the land. 



765. What is the estimated amount of salt in the sea ? 

 The amount of common salt in the various oceans is estimated at 



3,051,342 cubic geographical miles, or about five times more than 

 the mass of the mountains of the Alps. 



766. What is the depth of the sea ? 



The extreme depth has not, probably, been ascertained. But Sir 

 James Ross took soundings about 900 miles west of St. Helena, 

 whence he found the sea to be nearly six miles in depth. Now, if 

 we take the height of the highest mountain to be five miles, the 

 distance from that extreme rise of the earth, to the known depth of 

 the sea, will be no less than eleven miles. 



767. Why are the waters of some springs impregnated 

 ivith mineral matters ? 



