244 ELEMENTARY GENERAL SCIENCE CHAP. 



This experiment, also taken in conjunction with the previous 

 experiments upon the volumes of the gases, proves further that 

 one volume of oxygen is 16 times as heavy as the same volume 



of hydrogen, so that 1 litre of hydrogen weighs , that is, nearly 



09 gram (accurately '0896). 



Natural Waters. Water dissolves a larger number of things 

 than any other liquid, and is in consequence of the greatest use 

 to chemists. This explains why we cannot find pure water in 

 nature. No sooner has the rain formed than it begins to 

 dissolve various substances ; in its passage through the air it 

 takes up varying amounts of the constituents of the atmosphere, 

 such as carbon dioxide and oxygen, and when the surface of the 

 earth is reached the water dissolves out of the soil and the under- 

 lying rocks portions of all the soluble ingredients. The most 

 soluble bodies are naturally dissolved to the largest extent. It 

 will be seen later that the solvent property of water is consider- 

 ably increased by the presence of the carbon dioxide it obtains 

 in part from the air. When the amount of material dissolved 

 in water is very great it gives a distinctive character to the 

 liquid, which becomes known as a mineral water. Those natural 

 waters which contain a compound of sulphur and hydrogen, 

 called sulphuretted hydrogen, are spoken of as sulphur-water, if 

 some compound of iron is the substance which has been taken 

 up in large quantities, we have chalybeate waters formed. 

 Effervescent waters have a great amount of carbon dioxide 

 dissolved. 



EXPT. 249. Completely fill a flask with water and attach a 

 cork and delivery tube, dipping under a jar of water inverted 

 in a trough. Heat the flask and observe that dissolved air is 

 driven out. Collect the air and see that, since it supports 

 combustion, it contains oxygen. Prove also (by means of 

 lime-water) that it contains carbon dioxide. 



Hard and Soft Waters. It is a fact familiar to every one 

 that soap lathers very easily in some waters and not at all in 

 others. If rain-water be used, the lathering takes place with 

 great ease, while with the water which is supplied to some towns 

 a lather can only be made with difficulty ; and if we attempt the 

 same process in sea-water there is no lathering at all. Those 

 waters in which soap lathers easily are said to be soft. When such 

 is not the case the water is spoken of as hard. 



