WATER. 151 



Analysis and synthesis. These terms refer to two methods of 

 research in chemistry, accomplished by two kinds of reaction, ana- 

 lytical and synthetical. 



Analysis is that mode of research by which compound substances 

 are broken up into their elements or into simpler forms of combina- 

 tion, and analytical reactions are all chemical processes by which the 

 nature of an element, or of a group of elements, may be recognized. 



Synthesis is that method of research by which bodies are made to 

 unite to produce substances more complex. 



Analytical and synthetical methods, or reactions, frequently blend 

 into one another. This means : A reaction made with the intention 

 of recognizing a substance, may at the same time produce some com- 

 pound of interest from a synthetical point of view. 



Properties of water. Water is an inodorous, tasteless, and, in 

 small quantities, colorless liquid. Thick layers of water show a blue 

 color. On cooling, water contracts until it reaches the temperature 

 of 4 C. (39.2 F.), at which point it has its greatest density. If 

 cooled below this temperature it expands and the specific gravity of 

 ice is somewhat less than that of water. Water is perfectly neutral, 

 yet it has a tendency to combine with both acid and basic substances. 

 These compounds are usually called hydroxides (formerly hydrates), 

 such as NaOH, Ca(OH) 2 , etc. These compounds are often formed by 

 direct union of an oxide with water, thus : 



CaO + H 2 = Ca(OH) 2 . 

 SO 3 + H 2 O = SO 2 (OH) 2 . 



Water is the most common solvent, both in nature and in artificial 

 processes. As a general rule, solids are dissolved more quickly and 

 in larger quantities by hot water than by cold, but to this there are 

 many exceptions. For instance : Common salt is nearly as soluble 

 in cold as in hot water ; sodium sulphate is most soluble in water of 

 33 C. (91 F.), and some calcium salts are less soluble in hot than 

 in cold water. 



The term solution is applied to any clear and homogeneous liquid 

 obtained by causing the transformation of matter from a solid or 

 gaseous state to the liquid state by means of a liquid called a solvent 

 or menstruum ; solutions may also be obtained from two liquids, as 

 when we dissolve oil in ether. A solution is said to be saturated when 

 the solvent will not take up any more of the substance being dissolved. 



Two kinds of solutions are distinguished viz., simple solutions and complex 

 or chemical solutions. In the former we have a mere physical change, the mole- 



