40 EXPERIMENTAL GENERAL SCIENCE 



agreed that a cubic centimeter of water, when at its greatest 

 density, weighs a gram. If we know the density of a substance, 

 that is, if we know how much a cubic centimeter of it weighs 

 in comparison with water, we can easily ascertain its weight 

 by finding its volume in cubic centimeters and multiplying 

 this by its density. Suppose for instance that a body has a 

 density of 5. This means that a cubic centimeter of it weighs 

 five times as much as a cubic centimeter of water, or five 

 grams. If we had a volume of ten cubic centimeters, it would 

 weigh 5 times 10, or 50 grams. The density of a solid may 

 be determined in the first place by weighing it in air and again 

 in water. The second weighing is accomplished by attaching 

 it to a balance in such a way that it is immersed in the water 

 during the weighing. A substance weighed in water weighs 

 less than it does in air, and this difference in weight is the 

 weight of the water it displaces when immersed. In this way, 

 we find the weight of a volume of water equal to the volume 

 of the solid, and when this is compared with its weight in air, 

 we have its density. Suppose the weight in air of a given 

 substance to be 9 grams, and a loss of 3 grams in weight is 

 discovered when it is weighed in water. It is very evident 

 that the water it displaced must weigh 3 grams, and that the 

 substance is therefore three times as heavy as the same vol- 

 ume of water; that is, it has a density of 3. Though it is 

 usually more convenient to express density in grams per cubic 

 centimeter, we are not confined to that manner of expression 

 since density is a relative term. It can be as easily expressed 

 in grams per cubic foot, cubic inch, or other volumes. Gold 

 has a density of 19.3, therefore a cubic foot of gold would 

 weigh 19.3 times as much as a cubic foot of water, and a cubic 

 yard of gold would of course be 19.3 times as heavy as a cubic 

 yard of water. 



43. Specific Gravity. The term specific gravity is often 

 used to indicate the weight of substances in comparison with 



