46 



JUNIOR GRADE SCIENCE 



In using this relation between the volume and weight care must 

 be taken that the values of weight and volume are reduced to the 

 proper units. In all scientific work it is customary to adopt the 

 cubic centimetre and gram as the units of volume and weight 

 respectively. 



The ratio of the weight of any volume of a substance to the weight 

 of the same volume of water is equal to the relative density of the 

 substance, or, as it is frequently called, the specific gravity. 



19. DENSITY OF LIQUIDS. 



i. Use of a burette for finding the density of a liquid. Examine a 

 burette, noticing especially its division into cubic centimetres. Fill it 

 with liquid. 



Notice that the surface of the liquid is not flat but curved downwards, 



being higher near the sides of the 

 burette than at the centre. 



In reading the level of a liquid 

 having a surface of this kind, the 

 lowest part of the curved surface 

 should be observed, and the eye 

 should be brought on a level with 

 it, as shown in Fig. 36. 



A piece of paper held behind 

 the burette, opposite the eye, at 

 an angle of 45, is an assistance 

 in reading the graduations. 



Fill the burette with methylated 

 spirit. Make sure that the nozzle 

 is also filled, by running a little 

 of the liquid out. Weigh a small 

 beaker. Having noted the level 

 Fia. 36 Showing that an inaccurate read- o f t h e liquid in the burette, slowly 



rt ,^( fl,r> l,.i-..l ,,l' i;,,ni,l in a luln-Hi- id 



run into the beaker 10 c.c. of the 

 liquid and again weigh. Then 

 run in a further 10 c.c. and 

 weigh. If the weight of each quantity of liquid is not the same, run in a 

 further 10 c.c. and weigh. This weight should agree with one of the others. 

 If so it may be taken as accurate. 



Find the weight of 1 c.c. from two concordant results. 



Determination of the density of a liquid by means of a burette 

 and balance. It is sometimes desirable to be able to find the density 

 of a liquid without allowing it to touch the hands or even a duster, 

 as must be done in wiping the density bottle. In such a case a burette 

 may be used with advantage. For example, the density of strong 

 nitric acid may be determined, using a burette with a glass tap, by 

 running a known volume of the acid into a weighed stoppered bottle, 



ing of the level of liquid in a burette is 

 obtained, if the eye is not level with the 

 surface of the liquid. 



