Hydrometers of Total Immersion. 



503 



the hydrometer, which was only handled by the top of the 

 stem 



(For Liquids) 

 was removed from its wrappings, 

 wiped with a clean handkerchief, 

 and lowered slowly into the water. 

 The platinum-ring weights to the 

 calculated amount were boiled in 

 distilled water and then picked up, 

 one at a time, by a pair of ivory- 

 tipped forceps, and placed over the 

 stem of the hvdrometer. 



(For Solids) 

 with its contents of mercury alone , 

 or mercury and quartz, was slowly 

 lowered into the water. Any 

 small bubble of air on the sur- 

 face of the mercury was removed 

 by a glass pipette drawn out to a 

 capillary point. 



The beaker and contents were then transferred to the 

 incubator, and the hydrometer clamped into position by 

 lowering the funnel. The stirrer was lowered to the bottom 

 of the beaker, the thermometers put into their places, the 

 doors closed, and the microscope fixed in position. 



A preliminary experiment with the temperature changing 

 somewhat quickly was then generally made to ascertain ap- 

 proximately at what temperature the hydrometer and the 

 water had the same density. 



Each observation was made as follows : — 



1. The liquid was stirred. 



2. The hydrometer was liberated by raising the funnel. 



3. The thermometer was read. When the exact point was 

 being reached, the readings were made with the divisions both 

 in front and behind the mercury column. 



4. The hydrometer was observed to see whether it tended 

 to rise, to sink, or to occupy a position in the centre of the 

 liquid. 



Observations were repeated with the temperature rising or 

 falling until no difference could be observed between the 

 specific gravities of the hydrometer and water, or until two 

 temperatures, differing only by a few thousandths of a degree, 

 had been obtained at one of which the hydrometer was heavier 

 and at the other lighter than the water. 



When the point of identical density was being approached, 

 slight motions were imparted to the hydrometer by moving 

 the funnel sideways or raising the stirrer, in order that the 

 tendency of the hydrometer to sink or rise might not be masked 

 by its touching the side of the funnel. 



To repeat the experiment it was only necessary, if working 

 with a rising temperature, to open the incubator- doors and 

 waft in a little of the cooler atmospheric air, until the tempe- 

 rature of the water in the beaker fell a few hundredths of a 



2N2 



