38 WELLS'S NATURAL PHILOSOPHY. 



What is Ab- 71. The Absolute Weight of a body is 

 solute Weight f ||^g^^ ^^ j^g entire mass, without any reference 

 to its bulk, or volume. 



What IB spe- "^2- The Specific Weight, or the Specific 

 cific Weight? Oravity of a body, is the weight of a given 

 bulk, or volume of the substance, compared with the weight 

 of the same bulk, or volume, of some other substance. 



The term " Specific" Weight, or Gravity, is used, becauaa 

 the^t^rm^^Spey bodies of different species of matter have different weights 

 cific," as ap- under equal bullis, or volumes. Thus, a cubic inch of cork, 

 Vei^htT ^^^ ^ different weight from a cubic inch of oak, or of gold, and 



a cubic inch of water contains a less weight than a cubic inch 

 of mercury. Hence we say that the specific gravity, or specific weight, of 

 cork is less than that of oak or gold, and the specific gravity of mercury ia 

 greater than that of water. 



73. Specific Gravity, or Weight, being merely the compara- 



What is the ^^^q rrravity, or weight, it is convenient that some standard 

 Standard for , 7, , , ,,.,„, 



estimating the should be selected, to which all other substances may be re- 

 Specific Grav- ferred for comparison. Distilled water has accordingly been 

 taken, by common consent, as the standard for comparing the 

 weights of all bodies in the soUd, or hquid form. The reason for using dis- 

 tilled water is, that we may be certain of its purity. 



Water, therefore, being fixed upon as the standard, we determine the spe- 

 cific gravity of a body, or we ascertain how much heavier or ligliter a sub- 

 stance is than water, by the following rule: — 



How do we 74. Divide the weight of a given bulk of the 

 ci^c '^ra^^ substance, by the weight of an equal bulk of 

 of bodies? water. 



Explain the Suppose we take five vessels, each of which would contain 



application of exactly One hundred grains of water, and fill them respectively 



IS ru e. ^j^^ spirits, ice, water, iron, and quicksilver. The following 



differences in weight will be found : — The vessel filled with spirits would 

 weigh 80 grains; wiih ice, 90 grains; with water, 100 grains; with iron, 750 

 grains; with quicksilver, 1,350 grains. 



Water having been selected as the standard for comparing these different 

 weights, the question to be settled is simply this: How much lighter than 

 w.ater are spirits and ice, and how much heavier than water are iron and 

 quicksilver ; or, in other words, how many times is 1 00 contained in 80, 90, 

 750, and 1,350? The weights of the different substances fiUing the vessel 

 are, therefore, to be divided by 100, the weight of the water ; and there is 

 found for spirits the weight 0'80. one ifth lighter than water ; for the ice, 0-90, 

 one tenth lighter than water; for the iron, 7'50, or seven and a half times 

 heavier than water; for the quicksilver, 13-50, or thirteen and a half times 



