178 Domestic Science 



difference will be the excess of the weight of the gas 

 over that of the air. Find the weight of the air by 

 multiplying the volume of the flask in cubic centimetres 

 by 0-001293. (1 c.c. of air weighs 0'001293 g. at C. 

 and 760 mm. bar.) Add this to the difference of weight 

 as found above, and the sum will be the weight of the 

 carbon dioxide. The specific gravity of the carbon 

 dioxide is then readily found by the method given for 

 air above. 



Exercise for Student. 



Suggest any sources of error in the methods of Experiments 

 61 and 62. 



116. In Experiment 48 a method of checking the 

 accuracy of the position of the boiling-point of water, 

 as marked on a mercury thermometer, was described. 

 It was directed that the bulb of the instrument should 

 be placed in the steam from boiling water and the 

 reason for this direction will be next considered. 



EXPERIMENT 63. Using similar apparatus to that 

 shown in Fig. 44, determine the temperatures of the 

 steam arising from distilled water, tap-water, and 

 10 % and 20 % solutions of common salt, i.e. solutions 

 containing 10 g. and 20 g. of salt respectively in every 

 100 c.c. of solution. Each liquid should be boiled 

 in turn in the same flask and heated by the same source 

 of heat, while all temperatures registered should be 

 taken from the same thermometer. 



After recording the temperature of the steam in 

 each case, lower the thermometer into the boiling 

 liquid and note the temperature shown, together with 

 any variations which may occur as the period of boiling 

 is prolonged. 



