130 EXPERIMENTAL GENERAL SCIENCE 



remain in the liquid for a long time before settling to the bot- 

 tom. In such cases they are said to be suspended in it. 



109. Conditions Affecting Solution. The rapidity with 

 which a substance goes into solution depends somewhat upon 

 its temperature, the size of its particles, and whether the sol- 

 vent is still or in motion. When dissolving a solid, warming 

 the solvent not only causes the solid to dissolve faster, but 

 increases the capacity of the solvent for it, just as we have seen 

 that heating the air increases its capacity for moisture. At 

 zero Centigrade, 100 grams of water will dissolve 13 grams of 

 saltpeter, but if the water is warme'd to 20C., it will then dis- 

 solve 32 grams. Powdering the solid to be dissolved hastens 

 the process since it increases the surface which comes into 

 contact with the liquid. Shaking the solvent also hastens the 

 process since it removes the matter already dissolved from 

 the vicinity of the solute and allows more to be dissolved. 

 Although warming the liquid usually increases its capacity for 

 solids, it has the opposite effect on its capacity for gases. When 

 the temperature of the liquid containing the gas is increased, 

 the gas at once tends to escape. This is seen in a glass of 

 water left standing in a warm room for a time, the bubbles 

 formed on the sides of the glass being the gases driven out as 

 the temperature rose. 



110. Strength of Solution. The strength of a solution de- 

 pends upon the amount of the solute it contains. If very little 

 is present, it is said to be weak or dilute; if much is present, it is 

 strong. A concentrated solution is one that has been made very 

 strong, often by evaporating some of the solvent. A solution 

 that has all of the solid it can hold, is said to be saturated. If 

 the temperature of the solution is now increased it can take 

 up more of the solute, but if the temperature is lowered, 

 its capacity is decreased and some of the solute must be 

 dropped, just as cooling the air may cause it to drop some of its 

 moisture as rain. If the liquid containing the solid^evaporates, 



