142 Domestic Science 



tube between the marks already made into 10 equal 

 parts. 



The actual method of making a mercury thermo- 

 meter is very similar to that described above, but 

 precautions are taken with regard to the evenness -of 

 the bore of the tube, the dimensions of the bulb in 

 relation to the bore, and the expulsion of the last 

 traces of air in the filling, which are not necessary in 

 the performance of an experiment such as ours, in 

 which the illustration of the processes used rather than 

 the production of a standard article, is the chief point 

 to be considered. 



90. We obtained one of the points on our scale 

 by finding the level at which the liquid stood in the 

 bore of the thermometer when the bulb of the latter 

 was completely immersed in melting ice. The corre- 

 sponding point on the scale of a mercury thermometer 

 is obtained in a similar manner. 



EXPERIMENT 47. Check the accuracy of the freezing- 

 point as marked on the laboratory thermometers by 

 repeating that portion of the preceding experiment 

 dealing with the determination of this point, replacing 

 the alcohol thermometer by each of those to be tested 

 in turn. Allow each to remain in the ice till the mercury- 

 level remains steady for two minutes and note the 

 actual reading on the scale when this occurs. According 

 to the method of graduation adopted, the readings 

 should be for a Centigrade, and 32 for a Fahrenheit 

 thermometer. Unless the thermometers tested are 

 expensive ones, it will probably be noted that the 

 actual readings are slightly greater than they should be. 

 This is due to the fact that the bulb continues to con- 

 tract for a very long time after the making of the 

 thermometer, and hence the volume of mercury it can 



