Lesson VIII.] 



CHEMISTRY. 



117 



QUESTIONS. 



83. r. What do you mean by the 

 specific gravity of a body ? 



P. It is the ratio of its weight to the 

 weight of an equal bulk of another body, 

 taken as a standard [Experiment 12.] If 

 we fill one egg-cup with water and another 

 with mercury or quicksilver, we shall find 

 that although they both occupy the same 

 space, yet the mercury is 13$ times heavier 

 than the water, and hence we say that the 

 density of mercury is greater than that of 

 water. [See Q. 55, p. 15.] 



89. T. How is the density or specific 

 gravity of a body ascertained ? 



P. It depends upon the nature of the 



body. That of fluid* is easily obtained. 



For example, take a small bottle with a 



narrow neck (Fig. 20), and 



weigh it carefully. Then 



fill it with pure water up to a 



certain mark (a), and weigh 



it again. Now empty the 



bottle, dry it well, and fill it 



up to the same mark with any 



fluid say, for example, beer 



and weigh it again ; then 



divide the weight of the fluid, 



r,y. jo. (the beer) the specific gravity 



of which is required, by the weight of the 



water, and the product will indicate the 



specific weight By employing a vial that 



holds exactly 1,000 grains of water,* much 



time and trouble in calculating is saved, 



because we only require to weigh the 



liquid contained in the bottle, and its weight 



expresses its specific gravity. 



90. T. Is it necessary to be particular 

 with respect to the temperature of the fluid 

 to be weighed ? 



/' Yes; because we know that liquids 

 arc extremely expansible when heated ; 

 therefore, if one fluid (water) iswel. 

 60, and the other (spirit) at 70, it is 

 probable that you will not have weighed an 

 equal volume of each, because when they 



i reduced to the same 

 it will be found that the one that stood at 



Th*M botUTniar bVprocurtd for U. fid. 

 tach .of Mr.,- Ihormr.lt. * Wood, 



1M, N.w,.,.,tr..t. London, from whom any or 

 th apparatus UMd by Ga*or* 



y be purctuucd at a moderate ratt, ud 

 of tht belt quality. 



70 will occupy less space. It has, there- 

 fore, been found convenient to weigh all 

 bodies at a fixed temperature, such as 60 

 Fahrenheit Let us see how the 1,000 

 grain bottle acts. [Experiment 13.] I 

 have the bottle here ; it is filled with dis- 

 tilled water, at 60, and you see how correct 

 it is, for it weighs exactly 1,000 grains. 

 [Weighs it, then empties the bottle and 

 dries it]. We will now fill it with sul- 

 phuric ether, and weigh it [ Does so, and the 

 bottle is found to be too light]. You see 

 that it requires 270 grains to be placed in 

 the same scale with the bottle to balance 

 the 1,000 grains weight; therefore we say 

 that the specific gravity of the ether is 

 0730. Let us fill the bottle with sulphuric 

 acid instead of the ether, and observe what 

 takes place. [Does so, and the bottle 

 weighs down the 1,000 grains weight] 

 You see that we must add 875 grains to the 

 scale with the weight in it, consequently 

 the specific gravity of the acid is 1 



91. T. Is not the specific 

 gravity of fluids ascertained by 

 some other means than weighing 

 them ? 



/'. Yes ; by means of the hy- 

 drometer or areometer, which con- 

 sists of a hollow glass tube, with a 

 scale in the inside () so nrr 

 that it denotes the specific gravity 

 of lighter fluids by a scale with the 

 degrees proceeding from the bot- 

 tom to the top, and of heavier 

 fluids by the degrees proceeding 

 from the top to the bottom ; the' 

 end of the tube is blown out into 

 two hollow balls (Fig. 21), the 

 lower one containing mercury, so 

 ai to balance the instrument 

 Now, if we place this instrument 

 in .1 vessel containing a fluid, and 

 find that it marks 80 on the scale, 

 uc learn that 80 parts of the fluid 

 weigh as much as loo d w.itrr ; the spe- 

 cific gravity is therefore that of water M 

 100 to 80, or = ViP or 1>25 - 



/ How can you asccrt.v 

 uprcific gravity of a solid body f 



P. First weigh the body in t 1 

 then suspend it fnm the pan of a common 

 balance (Fig. 22, b), by a fine thread, and 



