iF 
Y 
TURPENTINE. 47 
be subtracted from the observed pressure reading to obtain the equivalent, or true, 
reading at 0° C. 
The distilling temperature of turpentine is affected plus (+) or minus (—) 0.057° C. 
for each millimeter variation of the barometer above or below the normal 760 mm. 
at 0° C.1 If the barometer reading, after correcting to 0° C., is below 760 mm., the 
turpentine will distill at a slightly lower temperature than nee normal pressure. 
‘Therefore, the temperature recorded at the beginning of distillation (and any others 
_ observed during the course of the distillation) must be corrected to get its equivalent 
at normal pressure. The final temperature observation point (170° C., of the speci- 
_fications) must be altered accordingly to get its equivalent at the pressure (corrected 
to 0° C.) at which distillation is made. 
For example, if the barometer reading, after correcting to 0° C., is 750 mm., the cor- 
rection of the observed initial distilling temperature will be 0.05710 Wim 0162 Cm 
approximately. If the reading of the thermometer when the turpentine begins to 
distill is 155.6° C., the corrected initial distilling temperature will be 155.6°+0.6° 
=156.2°C. Furthermore, the temperature observation point at the end of distillation 
(170.0° G. at 760 mm.) must be altered to the same extent. Since the turpentine is 
distilling 0.6° C. below what it would at normal pressure, distillation must be dis- 
continued at0.6° C. below the specified limit of 170.0° C. to determine the percentage 
distilling below 170.0° C. 
If the barometer reading corrected to 0°C. is above 760 mm., subtract the temper- 
ature correction from the observed thermometer reading to determine the initial dis- 
tilling point, and continue distillation to 170.0° C. plus the correction to determine 
the percentage distilling below 170.0° C. 
(g) Polymerization.—Place 20 cc. of 38 N (equivalent to 100.92 per cent H,SO,) 
sulphuric acid in a graduated, narrow-necked Babcock flask, stopper, and place in 
ice water tocool. Addslowly, from a pipette, 5cc. of the turpentine to be examined. 
Gradually mix the contents, keeping warm, but being very careful that the tempera- 
ture does not rise above 60° C. When the mixture no longer warms up on shaking, 
agitate thoroughly and place the flask in a water bath and heat at 60° to 65° C. for not 
less than 10 minutes, keeping the contents of the flask thoroughly mixed by vigorous 
shaking for one-half minute each time, six times during the period. Do not stopper 
the flask after the turpentine has been added, as it may explode. Cool to room tem- 
perature, fill the flask with concentrated sulphuric acid until the unpolymerized oil 
rises into the graduated neck and centrifuge from four to five minutes at not less than 
1,200 r. p. m., or for 15 minutes at 900r. p. m., or allow tostand, lightly stoppered, for 
12 hours. Calculate the percentage, note the consistency and color, and determine 
the refractive index (at 20° C.) of the unpolymerized residue. The consistency should 
be viscous and the color straw or darker. 
REAGENT FOR TESTING.—In a weighed glass-stoppered bottle (the regular 23-liter 
acid bottle is of a convenient size) mix ordinary concentrated sulphuric acid (sp. gr. 
1.84) with fuming sulphuricacid. Ifthe fuming acid used contains 50 per cent excess 
SO,, the ratio of one part, by weight, of the former to three-fourths of a part, by weight, 
of the latter will give a mixture slightly stronger than the required strength. To de- 
termine the exact strength of this mixture in terms of H,SO,, weigh exactly, in a 
weighing pipette of about 10 cc. capacity, approximately 20 grams of the acid. Allow 
it to flow down the sides of the neck into a 1,000-cc. volumetric flask containing about 
200 cc. of distilled water. When the pipette has drained, wash all traces of the acid 
remaining in the pipette into the flask, taking precautions to prevent loss of SO3, and 
make up to the mark. Titrate 20-cc. portions, drawn from a burette, against half 
normalalkali. Calculate the concentration in terms of the percentage of F,SO, in the 
sample taken. 
1 Landolt-Bérnstein Physikalisch-Chemische Tabellen, Ed. 4, Table 127, p. 435. 
2 
