136 METHODS OF TESTING BABCOCK MILK BOTTLES. 



These results correspond exactly with the change in volume, 

 as calculated above, that would be brought about by a change 

 of 1°C. in temperature in the amount of mercury (700 grams) that 

 fills a bottle of this size. Hence the lowering of the level of the 

 mercury in the neck is practically all due to the fall in temperature 

 that takes place in the mercury when cooling down to the room 

 temperature, after the slight rise that took place when pouring it 

 into the bottle. 



4. Owing to the large weight of mercury in the bottle, with 

 the consequent loss of sensitiveness in the balance used, it inay 

 be possible to have an error of as much as 0'02 gram when 

 weighing. Now 0'02 gram of mercury occupies a volume of 

 0'0015 c.c, or nearly O^Ol per cent, on the Babcock scale, which, 

 however, is within the limit of error in reading the scale. 



5. Any dust, or dirt of any description, in the bottle fouls 

 the surface of the mercury, thus adding to the difficulty of 

 reading the level correctly. 



From the above results and remarks it is seen that the 

 volumetric method given is a fairly reliable method for calibrating 

 Babcock milk test bottles, and is the best one of the three 

 mentioned for ordinary use, when a large number of bottles have 

 to be tested, and when no elaborate precautions can be taken to 

 secure uniformity in the conditions of working, especially as 

 regards temperature. 



