48 Testing Milk and Its Products. 



and dry test bottle. Since the specific gravity of mer- 

 cury is 13.59, double this quantity will occupy a volume 

 of exactly 2 cubic centimeters (48). The neck of the 

 test bottle is then closed with a small, smooth and soft 

 cork, or a wad. of absorbent cotton, cut off square at one 

 end, the stopper being pressed down to the first line of 

 the graduation. The bottle is now inverted so that the 

 mercury will run into its neck. If the total space in- 

 cluded between the and 10 marks is just filled with the 

 two cubic centimeters of mercury, the graduation is cor- 

 rect. Bottles, the whole length of the scale of which 

 vary more than two-tenths of one per cent., are inaccu- 

 rate and should not be used. 



The mercury may be conveniently transferred from one 

 test bottle to another, by means of a thin rubber tube 

 which is slipped over the end of the necks of both bot- 

 tles, and one weighing of mercury will thus suffice for a 

 number of calibrations. In transferring the mercury, 

 care must be taken that none of it is lost, and that small 

 drops of mercury are not left sticking to the walls of the 

 bottle emptied. A sharp tap on the bottle with a lead 

 pencil will help to remove minute drops of mercury from 

 the inside of it. Unless the bottles to be calibrated are 

 perfectly clean and dry, it is impossible to transfer all 

 the mercury from one bottle to another. 



After several calibrations have been made, the mer- 

 cury should be weighed again in order to make certain 

 that none has been lost by the various manipulations. 

 The scales, figs. 33 and 34, shown in (94), are sufficiently 

 delicate for making these weighings. 



54. Cleaning mercury. Even with the best of care, 

 mercury used for calibration of glassware will gradually 



