GENERAL PRINCIPLES 25 



of matter, it remains to be proved that the nature of that matter 

 does not modify the value of the mass. 



When speed and acceleration are communicated to bodies in 

 a brief interval of time the effects of inertia can be appreciated. 

 A traveller who gets out of a carriage in motion may fall because 

 his body has retained the movement of the carriage. The same 

 effect is utilised by the workman who hits the back of a plane to 

 release the iron ; the blade has resisted by its inertia. In the 

 same way the head of a hammer is driven into its handle by 

 striking the end of the handle on the bench. Instantaneous 

 speed and force do not exist, but a force can act in a very short 

 space of time, causing shock ( 41). 



19. The smallest mass of a body that has the properties of 

 matter is the mass of the molecule. A molecule is not necessarily 

 indivisible ; it can be composed of atoms which are themselves 

 theoretically indivisible. The properties of matter are generally 

 considered in relation to the molecule. 



Analysing the constitution of the molecule, chemistry has 

 established that it is composed of a single atom in the case of 

 mercury, of two in that of oxygen, etc. The signs are Hg for the 

 one, O 2 for the other. The molecules can be condensed and 

 pass from the gaseous to the liquid or solid states. 



Composite bodies, acids, bases, salts, etc., have polyatomic 

 molecules. The most complex molecular constructions are found 

 in organic substances such as in albumen (white of egg). The 

 weight of a molecule is the sum of the weight of the atoms of 

 which it is composed assuming H = 1 gramme as the atomic 

 weight of hydrogen, the atomic weight of all elements has been 

 determined. For example : 



H = 1 (hydrogen) S = 32 (sulphur) 



O = 16 (oxygen) ' C = 12 (carbon) 



N = 14 (nitrogen) P = 31 (phosphorus) 



Consider a molecule of glucose. It contains 6 atoms of carbon, 

 6 of oxygen, and 12 of hydrogen. It is represented thus : 

 Glucose = C 6 H 12 6 



The molecular weight is 



(12x6) -f (1x12) + (16x6) = 180 grammes. 

 The molecule of water is H 2 O =18 grammes, and so on. 



It is a remarkable thing that the biological properties of a mole- 

 cule depend not only on its nature, but also its form. Thus a 

 certain microbe will ferment a sugar of which the atoms have a 

 certain arrangement, but it will not ferment another of the 

 same composition and the same molecular weight, if the atoms are 

 differently arranged. 



