176 



Domestic Science 



115. A corresponding diminution of volume occurs 

 when steam condenses, and this is taken advantage 

 of in a simple method whereby an 

 approximate determination of the 

 specific gravity of air maybe effected. 



EXPERIMENT 61. Fit a round- 

 bottomed flask of about 500 c.c. 

 capacity with a rubber stopper, 

 bored to receive a short glass tube. 

 To the other end of this tube attach, 

 by means of stout rubber tubing, 

 a second short length of glass tube. 

 Fix a small screw clamp on the 

 rubber tubing . The general arrange- 

 ment of the apparatus is shown in 

 Fig. 54. The wire shown is for 

 suspending the apparatus from the 

 hook at the end of the arm of a 

 balance while weighing. Pour about 50 c.c. of distilled 

 water into the flask. Heat this to boiling-point, and 

 allow the heating to continue till most of the water has 

 boiled away. In this manner practically all the air 

 is displaced by steam. While still boiling, clamp the 

 rubber tube, and at once remove the source of heat. 

 Let the flask cool and then weigh it carefully. Next 

 open the clip gradually. The greater part of the 

 steam has condensed during the cooling and thus 

 produced a considerable decrease of pressure within 

 the flask, so that the opening of the clip is attended 

 by an inrush of air from the room until the pressure 

 inside the flask has reached atmospheric pressure. 

 When no more air enters, weigh the apparatus 

 again. The gain in weight will be the weight of the 

 air which has entered the flask. To find the volume 



Fig. 54. 



