34 BULLETIN 898, U. S. DEPARTMENT OF AGRICULTURE. 
Table 5 has been compiled to show the weight of a gallon of turpen- 
tine at temperatures varying from 20° F. (—6.7° C.) to 110° F. 
(43.3° C.). Experiments performed in the Bureau of Chemistry have 
shown that the coefficient of expansion of turpentine at temperatures 
down to 5° C. (41° F.) is the same as at higher temperatures. It 
was assumed, therefore, that the coefficient of expansion would be 
practically the same at a slightly lower temperature, since this 
temperature (20° F.) is still far above the freezing point of turpentine. 
In order to use Table 5 it is necessary to know the specific gravity 
of the turpentine at 15.5° C., or 60° F., which is usually and most 
easily determined by means of a Westphal balance or a hydrometer. 
Hydrometers are constructed to read in terms of specific gravity, in 
terms of density (p. 28), or in terms of Baumé degrees. To make 
possible the use in connection with Table 5 of a Baumé hydrometer, 
Table 6, giving the specific gravity at 15.5°/15.5° C. (60°/60° F-.) 
corresponding to various Baumé readings, was compiled. Since the _ 
Baumé scale for light liquids in general use in the United States is 
140 
~ sp. gr. 60°/60° F. 
dent that readings on a Baumé hydrometer bear a direct relation to 
specific gravity at 60°/60° F. only and must be taken at 60° F. 
Gigr oss): 
On the other hand, hydrometers reading in terms of specific gravity 
may be used at temperatures slightly above or below the base temper- 
ature for which they are calibrated without introducing a material 
error in the result. For example, if a hydrometer calibrated to give 
specific gravity at 20°/20° C. is used at 25° C., the resulting reading 
~ (disregarding a negligible error due to the expansion of the glass of 
which the hydrometer is made) will be the specific gravity at 25°/20° 
C. instead of 20°/20°C. Similarly, if a hydrometer calibrated to give 
specific gravity at 15.5°/15.5° C. is used at 20° C., the resulting reading 
will be the specific gravity at 20°/15.5° C. Tables 7 and 8 are used 
to determine the required specific gravity at 15.5°/15.5° C. (60°/60° 
F’.) corresponding to readings obtained with a 15.5°/15.5° C. (60°/60° 
F’.) or a 20°/20° C. (68°/68° F.) hydrometer, respectively, at various 
temperatures within the limit of negligible error. Table 7 may be 
used also in connection with a 15°/15° C. hydrometer, as the error thus 
introduced is negligible. If possible, it is always better to make the 
specie sravity determination at the temperature for which the 
hydrometer is calibrated. 
If a hydrometer calibrated to read in terms of density is used as on 
a 15.5°/4° C. or a 20°/4° C. basis, the temperature of the liquid at the 
time of obsery ving the density should be exactly 15.5° C. or 20° C., as 
the case may er To convert the reading to specific ee at 
15.5°/15.5° C., add 0.0008 to the density at 15.5° C., or 0.0045 to the 
density at 20° C, 
based on the formula, degrees Bé — 1380, it is evi- 
