MEASUREMENT OF DENSITY 47 



and finding the weight of it. By calculation the weight of 1 c.c. can 

 be found. 



To ensure accuracy in reading the burette, it is advisable to find the 

 weight of a number of equal volumes. With accurate manipulation 

 the weights are equal. 



20. USE OF A DENSITY BOTTLE. 



i. Take a narrow mouth stoppered bottle of about 4 oz. capacity, and 

 file a vertical groove upon the stopper. Weigh the bottle, Fill it with water 

 and insert the stopper so that the bottle is completely filled. Wipe away 

 from the rim the water that has escaped through the 

 file mark, and again weigh. What mass of water does 

 the bottle hold ? Hence what volume of any liquid ? 



Again fill the bottle with methylated spirit, vinegar, 

 turpentine, ink, or any other liquid, and find the mass 

 of each liquid the bottle contains when full. As you 

 know the volume, calculate in each case the density. 



ii. Weigh some small pieces of lead and place them 

 in the bottle. Fill the bottle with water and shake it 

 in order to get rid of air bubbles ; then insert the 

 stopper, wipe the bottle, and weigh. How much less 

 is the mass than the total mass of the lead and the 

 bottle of water ? This is obviously the mass of water 

 forced out by the lead. What is its volume ? and what 



then is the volume of the lead ? Hence find the density , r * G ; 37 ~. A bot t ]e 

 i i J for determining rela- 



of the lead. tive dengity 



iii. Find by the method used in the preceding experi- 

 ment, the densities of such things as tin tacks (these are really made of iron), 

 bits of slate pencil, brass wire or brass nails. 



In all the above experiments it has been assumed that the mass of 1 c.c. 

 of water is exactly 1 gram. As this will be later found to be only the case 

 at 4 C., the experiments have really only given the relative density with 

 respect to water at the temperature of the experiment. The difference, 

 however, will be very small. 



Determination of relative densities by relative density bottle. 

 A simple method of determining the relative densities of substances is 

 to use a specific gravity or relative density bottle. Such a bottle often 

 consists of a small glass flask, holding about fifty grams of water. It 

 is provided with a nicely- fit ting ground stopper, with a very small bore 

 through it or a vertical groove cut upon it (Fig. 37). To use the bottle 

 in determining the relative density of liquids and powders, the weight 

 of the empty bottle and stopper must first be known. The 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 



