10 



TESTING MISCELLANEOUS SUPPLIES. 



5. Calibration of Pyknometers. 



Clean and dry the pyknometer and weigh carefully after it has stood in the 

 balance case for about thirty minutes. Fill with freshly boiled distilled water at 

 about 14 C., insert the stopper, and place in a bath kept at exactly 15.5 C. 

 When the temperature of the water in the pyknometer has risen to 15.5 C., 

 u Inch will be shown by the water ceasing to rise out of the capillary tube of the 

 stopper, wipe off the water on the top of the stopper, place the cap on the stopper, 

 remove from the bath, wipe dry, and let stand until it has come to room tem- 

 perature, then weigh. This will give the water value of the pyknometer at 

 15.5 C. Calibrate the same pyknometer at 50 C., proceeding in the same way, 

 except that the water used in filling the apparatus is about 47 C. and is 

 brought up to 50 C. in a bath kept at exactly that temperature. Multiply the 



weight of water at 50 C. by 



=1.011125. This product is the water value 



of the pyknometer at 50 C. In determining the specific gravity of any oil pro- 

 ceed as in calibrating, only substitute the oil for the freshly boiled water, and 

 divide the weight of oil by the water value of the pyknometer. Results are 



1^5 ''i C 1 ^50 C 1 

 expressed in specific gravity at ^5 5 Q or -^ 5 Q If it is desired to calibrate 



the instrument at any other temperature, proceed in a similar manner and 

 multiply the weight of water found by the density of water at 15.5 C. (0.99905) 

 and divide by the density at the temperature used. (Use the tables of Landholt, 

 Bernstein, and Meyerhofer, previously mentioned, page S.) 



A plummet may be calibrated in a similar manner by calculating the water 

 equivalent at 15.5 C. ef the volume displaced at the different temperatures. 



6. Hydrometers. 



Hydrometers are frequently used by oil chemists, and when properly made 



are very j: 1 instruments. They should be calibrated at 15.5 C. (60 F.) and 



used at that temperature when exact results are desired. If a hydrometer is 



T 

 used at any other temperature (T,), the results should be recorded at 1f - K0f ^ 



and also reduce, I t<> 



i :..:. C. 



by applying the formula: G=G'+K (T 15.5 C.). 



15.5 C. 



Unless the determination is made at the temperature at which the hydrometer 

 is calibrated the result should not be relied on beyond the third place. If 

 more exact results are desired, do not use a hydrometer. 



7. Arbitrary Scales. 



Tll(> ' M Tie gravity in terms of arbitrary scales, such as Baume, 



is very objectionable, since there are a number of Baume tables in print which 

 differ widely. It is sometimes necessary, however, to report specific gravity 

 In degrees Baume. When this is the case determine the specific gravity in the 

 usual mam., i. mince, if necessary, to^'C-, and find the degrees Baum by 



!>..) t^i. 



i" an American standard table. Such a table has been recalculated 

 ami published by I lie Bureau ,,f Standards, Circular 19, and is calculated by 

 means of the following formulae: 



F<>r liquids lighter than water: II 

 I "i liquids heavier (ban water: 



Specific gravity at 15.5 C. 



130. 



145 



Specific gravity at 15.5 C. 



