SPECIFIC GRAVITY DETERMINATIONS. 



9 



O.//TJ/TZ 

 snefer 



4. Choice of Pyknometers. 



For the most accurate work with very fluid oils the Sprengel tube is the most 

 accurate form. This apparatus is difficult to clean, and for ordinary work a 

 specific-gravity bottle, with a cap to take up expansion, is the most convenient. 



A thermometer as part of the 

 apparatus adds to the cost and 

 has little or no advantage; in 

 fact, it has some distinct dis- 

 advantages. Aside from errors 

 in the thermometer, the liquid, 

 if placed in the pyknometer at 

 a low temperature and then 

 allowed to stand at room tem- 

 perature until the thermometer 

 registers 15.5 C., may not 

 be of the same temperature 

 throughout. If a pyknometer 

 without a thermometer is used, 

 it is necessary to bring it to 

 its final temperature by keep- 

 ing it in a bath for some time. 

 By filling the pyknometer at 

 about 14 C., inserting the stop- 

 per, and then placing it in a 



O.I mm diameter 

 of/io/e 



- -2mm diameter 

 of fio/e 



FIG. 1. Pyknometer for very fluid liquids 

 (actual size). 



FK;. i'. Pyknometer for vis- 

 cous liquids (one-half act- 

 ual size). 



ith which is kept at 15.5 C. until no more liquid rises out of the capillary tube, 

 one may be sure that the whole of the liquid in the pyknometer is at 15.5 C. 



The form of pyknometer shown in figure 1 is excellent for very fluid oils, 

 but it is not suitable for those that are very viscous. For the latter use the 

 form shown in figure 2. 



21694 Bull. 100 12 2 



