WATER 



419 



longer tube and the air is expelled through the shorter 

 tube. The bubbles of air can be seen or heard rising 

 through the water, until the bottle is nearly full, a 

 small volume of compressed air remaining in the neck 

 of the bottle. 



As the apparatus is raised, the air thus imprisoned 

 expands, and prevents the entry of more water from 

 nearer the surface. 



FIG. 205. Ice-box for transmission of water samples, etc. 



Transport of Sample. If the examination of the sam- 

 ple cannot be commenced immediately, steps must be 

 taken to prevent the multiplication of the bacteria con- 

 tained in the water during the interval occupied in transit 

 from the place of collection to the laboratory. To this 

 end an ice-box such as that shown (in Fig. 205) is essen- 

 tial. It consists of a double- walled metal cylinder into 

 which slides a cylindrical chamber of sufficient capacity 

 to accommodate four of the 60 c.c. bottles; this in turn 

 is covered by a metal disc the three portions being 



