4 ANATOMY FOR NURSES [Chap. I 



two hydrogen atoms and one oxygen atom (II2O), when sepa- 

 rated, water gives the two elements hydrogen and oxygen. Again, 

 sugar is composed of hydrogen, carbon, and oxygen, each mole- 

 cule having in it twelve atoms of carbon, twenty-two atoms of 

 hydrogen, and eleven atoms of oxygen (C12H22O11), when sepa- 

 rated it gives several compounds with simpler molecules, as car- 

 bon dioxide (CO2), water (H2O), methane (CIi4), etc. 



Mixtures. — A mixture can be made up of either or both ele- 

 ments and compounds. These can often be separated by simple 

 physical means, as filtration or evaporation. ]\Iilk is a mixture of 

 several compounds, — water, cream, proteins, sugar, and salts. 

 The cream can be separated by allowing the milk to stand, when 

 it will rise to the top, and can be skimmed off. Salt solution is 

 a mixture of the compounds, salt and water. They can be sepa- 

 rated by evaporating the water. Air is a mixture of compounds 

 and elements, carbon dioxide (compound), nitrogen and oxygen 

 (elements). They cannot be separated bj' any simple means. 



3. Matter undergoes changes. 



Physical change. — When matter has been subjected to a 

 change which does not affect the composition of the matter, the 

 change is said to be a physical one only. The following are 

 given by way of illustration : — 



Water can solidify (freeze) or it can vaporize ; whether it exists 

 in the state of a solid, a liquid, or a gas, depends upon the tempera- 

 ture, but the composition in all these states is identical. Sugar 

 melts, but the solid sugar and the liquid sugar are exactly the same 

 in composition ; the change is only one in physical state. 



Other physical changes besides change in physical state are, 

 change in size, 'position, magnetic or electric condition, and change 

 in temperature. 



Chemical change. — V^Tien matter undergoes a change in com- 

 position, it is said to have undergone a chemical change. The 

 following are illustrations : when an electric current is passed 

 through water, the water is separated into two distinct substances, 

 hydrogen and oxygen. In this case we start with a single com- 

 pound (water) of definite composition, and as a result of the 

 change, obtain two different substances (oxygen and hydrogen). 

 Again, in a bar of iron there is nothing but the element iron, 

 but if it is left exposed to the air, it is converted into a red 



