MEASUREMENT OF QUANTITY OF MATTER 11 



volume equal to that of 1,000 cubic centimetres [written 1,000 

 c.c.] is called a litre. 



The final authority for the unit quantity of matter in the 

 C.G.S. system, and the standard by which it must be deter- 

 mined, directly or indirectly, is the Kilogramme des Archives, a 

 piece of platinum adjusted by Borda. 



The gram is '001 of this piece of platinum. 



All distances must be compared, directly or indirectly, with 

 the distance between the ends of a rod of platinum when it is 

 at the temperature of melting ice. This is the standard 

 metre made by Borda in 1795. The centimetre is equal to 

 01 of this distance. 



The metre was selected as being the ten-millionth part of 

 a quarter of the earth's circumference, so that all lengths 

 might be compared with the circumference of the earth, a 

 length looked upon as permanent, and hence always capable 

 of being redetermiiied. That the earth's circumference should 

 be commonly referred to as the standard is, however, impossible, 

 and the alternate authority is now the length of the platinum 

 rod made by Borda. 



Having fixed on a distance and called it a metre, a piece 

 of platinum was prepared containing the same quantity of 

 matter as a cubic decimetre of pure water at 4 C. This was 

 called a 'kilogramme.' Hence a cubic centimetre of such 

 pure water would have a mass of 1 gram. This process was 

 adopted with the intention of being able to re-establish the 

 unit of mass, if necessary, from the unit of length, but this 

 is practically very difficult, and moreover the supposed 

 relation is only approximate. Hence both the metre and 

 kilogramme are arbitrary standards. 



It is part of the same uniform system to take a density 

 of 1 gram per cubic centimetre as unit of density. It was 

 intended to make the density of water unit, and it is very 

 nearly so, for it contains approximately the unit quantity of 

 matter in the unit volume. A body which contains 2 grams 

 per c.c. would have a density denoted by 2, and so on. 



The number expressing the magnitude of a given den- 

 sity is determined by finding the number of units of mass it 



