60 



ELEMENTS OF LABOKATOKY WORK 



We may be helped to do so by observing the result of adding 

 to one of the columns a known quantity of water. 



Cork one of the branches tightly, and fill it with water by 

 inverting the vessel. Add or remove water till the level 

 stands a short way up the other branch. Then add successive 

 equal quantities of water, say 5 c.c., from a burette, and mark 

 each level upon a strip of paper gummed along the branch, or 

 else mark the glass with a diamond. Calibrate the other 

 branch similarly, starting, for convenience, at the same level. 

 The distance between each mark in each branch may now be 

 divided into five equal parts, and the columns will be calibrated 

 in cubic centimetres with sufficient accuracy. 



a 



Fig. 18. 



B 





Water is now added to this calibrated vessel, and the level 

 in each limb noted. Five cubic centimetres of water are now 

 dropped from the burette into the narrow branch, and the 

 levels again noted. Had there been no movement of the liquid, 

 the addition of 5 c.c. of water would have raised the level 

 through a vertical distance which is easily measured from the 

 graduated marks by a scale. But this level has now changed 

 through a measurable distance and we may say that 5 c.c. of 

 water have moved through this distance, while the change of 

 level in the other limb enables us to calculate what quantity 

 of water has been simultaneously raised through a measurable 

 distance. 



It should be found that the quantities of water are in- 

 versely proportional to the distance through which they have 

 been displaced, and we have the same kind of change as 

 in the lever, illustrated under somewhat analogous conditions. 

 In this calculation we assume that there is no alteration of 



