YII PRINCIPLE OF ARCHIMEDES 99 



bottle is then filled with pure water, the stopper inserted, and 

 the water which is forced through the hole in the stopper wiped 

 off, and the bottle and its contents weighed. In this way the 

 weight of water which just fills the bottle is found. If now we 

 empty the bottle and carefully dry it inside and out, and fill it 

 with the liquid of which the density is required, say spirits of 

 wine, and weigh again, we have the weight of the liquid which 

 just fills the bottle, or the weights of equal volumes of the 

 liquid and water, the proportion of which gives us the relative 

 density of the liquid. Instead of a bottle of this kind, a flask 

 having a narrow neck around which a mark has been made may 

 be used, or, any bottle with a vertical file mark made on the 

 stopper, will do. The weight of water which fills the bottle up 

 to the mark may thus be compared with the weight of liquid 

 which fills it to the same mark. 



EXPT. 93. Counterpoise an empty specific gravity bottle, 

 or a flask having a mark on its neck. Fill the flask up to the 

 mark with methylated spirit and weigh it ; then empty the 

 flask, dry it, and fill with water up to the same mark. Weigh 

 again, and from the two weights find the relative density of 

 the spirit, remembering that 



weight of substance 

 Relative density = we ight of equal vol7of"Vater 



EXPT. 94. Following the method of the previous experi- 

 ment, determine the relative densities of two or three liquids, 

 such as turpentine, milk, vinegar, beer, wine, sea-water or a 

 solution of salt, and ink. 



EXPT. 95. Weigh out about 100 grams of shot. Fill the 

 specific gravity flask with water, and counterpoise it together 

 with the shot. Next put the shot into the bottle, and remove 

 the water displaced. Add weights until the index of the 

 balance swings evenly. The weights added must equal the 

 weight of the water displaced, that is, the weight of a volume 

 of water equal in volume to the shot. Therefore 



Relative density of the shot = weight of shot 



weight of water displaced 



EXPT. 96. Find by the method used in the preceding ex- 

 periment the relative densities of such common things as tin 

 tacks (which are really made of iron), bits of slate pencil, 

 brass wire, and brass nails. 



H 2 



