WATER. 207 



stirred with water, it is said to be diffused, instead of 

 dissolved. The solvent action of water plays a most 

 important part in nature, as will be seen in the conclu- 

 ding chapter of this work. The subjects of solution, 

 and precipitation, are more fully considered in the 

 chapter on Salts. 



Wkatispre- ^10. PRECIPITATION. Where a substance 

 dpitation ? which has been dissolved, is re-converted 

 into a solid form, it is said to be precipitated. 

 Thus, when air from the lungs is blown 

 through a quill or pipe-stem into water, the 

 lime combines with the carbonic acid from the 

 lungs, and falls to the bottom of the vessel, in 

 the form of solid particles of chalk. The 

 solid thus produced, is called a precipitate. 



511. FILTRATION. Filtration is 



What is filtra- 

 tion, and hoio the separation of a precipitate 



is it effected? from the Uquid m which it j g con- 



tained. This is effected by throwing the mix- 

 ture into a paper cone, which retains the 

 solid, while the liquid passes through its pores. 

 Such a filter is prepared by folding unsized paper into 

 the shape of a quadrant, which is then opened, so as 

 to form a cone, commonly supported in a glass funnel. 

 It is possible, in small experiments to dispense with the 

 funnel, as is done in the figure, and even to use ordi- 

 nary newspaper, in the place of that especially pre- 

 pared for the purpose. 



