WATER 223 



that is, the molecules of the substance are split up into two parts, each 

 part being charged with equivalent quantities of opposite kinds of elec- 

 tricity. These charged particles are called ions, and a compound which 

 yields ions is called an electrolyte ; all others, such as sugar, for in- 

 stance, are called non-electrolytes. Solutions of the former will easily 

 conduct an electric current, while solutions of the latter will do so no 

 more than the pure water itself. Of all common liquids which dissociate 

 substances, water has the highest power. It is dissociated itself only to 

 the very slightest extent. 



A fact which can be explained only by the theory of electrolytic 

 dissociation is, that whenever an acid in solution is acted upon by 

 an equivalent quantity of a base in solution, both solutions being dilute, 

 and no matter what the acid or base, the same amount of heat is lib- 

 erated in the reaction. The only thing here which can and does take 

 place is for the hydrogen ion, which is the essential part of the acid, 

 to combine with the so-called hydroxy 1 ion, the essential part of the 

 base, to form a definite quantity of water, the same in every case, and 

 hence giving off the same quantity of heat. The other parts of the 

 acid and base remain unchanged, as ions, in the solution. In concen- 

 trated solutions, other factors come into play which necessarily cause 

 the amount of heat to be variable. 



We see from the above that water instead of being a side i?sue in 

 chemical reactions, as we have been prone to place it, is really the most 

 important and most fundamental thing in them. Moreover, it is made 

 up of what constitutes both acid and base and yet has not the slightest 

 trace of the properties of either. It is perfectly neutral. 



When a soluble solid, no matter how great its specific gravity, is 

 placed in the bottom of a vessel and is covered with water, it will in 

 time diffuse through the entire liquid until the whole is perfectly 

 homogeneous, even though the force of gravity is pulling continually 

 against it, tending to keep it at the bottom. Diffusion is said to be due 

 to osmotic pressure, but as this has never been explained satisfactorily, 

 we are about as far from answering the question as to its cause as if we 

 had left it alone. All we know of osmotic pressure is, that if we sepa- 

 rate two solutions of different concentrations by a membrane, water will 

 pass through the membrane from the more dilute to the more concen- 

 trated solution, which, if the latter side is enclosed, will set up a pres- 

 sure on that side. This is called osmotic pressure, and there are certain 

 laws governing it. These have been thoroughly studied and have been 

 shown to correspond exactly to the laws of gases, but the cause for the 

 pressure is as yet unknown. Diffusion is not a property of water only, 

 but of all liquids. However, it has been studied in the case of water 

 more thoroughly than in any other. 



Another property of all liquids which has a special interest where 



