46 BULLETIN 898, U. S. DEPARTMENT OF AGRICULTURE. 
containing high-boiling mineral oil or glycerin and fitted with a concave cover having 
in the center a circular opening 54 to6cm.in diameter. Inall cases take the necessary 
precautions to prevent fluctuation in temperature in the neck of the flask. 
Thermometer.—The thermometer used for turpentine a shall conform to 
the following specifications: 
It shall be graduated from 145° to at least 200° C. in 0.2° intervals. Thermometers 
graduated above 200° C. may be used, provided they also comply with the following 
requirements: Length, bottom of thermometer to 175° mark, not more than 8 nor less 
than 6.5 cm.; length, top of bulb to 145° mark, not less than 1.5 cm.; length, 145° 
to 175° mark, not more than 6 ‘cm. 
The thermometer shall be made of suitable thermometric glass and thoroughly 
annealed, so that the scale errors will not increase after continued heating. 
The thermometer shall be filled above the mercury with an inert gas, with sufficient 
pressure above the mercury column to prevent breaking of the column. It shall 
have a reservoir at the top, so that the pressure will not become excessive at the highest 
temperature. 
e 
Every fifth graduation shall be longer than the intermediate ones, and the marks ' 
shall be numbered at each interval of 5°. The graduation marks shall be clear-cut 
and fine and the numbering clear-cut and distinct. 
The error at any point on the scale shall not exceed +0.5° C. when tested for total 
immersion of the mercury column. 
Receiving cylinder.—Collect the distillate in an accurately graduated 50 or 100 ce. 
cylinder. The so-called normal or precision cylinder of 50 cc. capacity, having an 
internal diameter of 1.5 cm. and graduated in 0.2 cc., is preferred. If a cylinder 
with larger inside diameter is used, a pasteboard cover should be placed over the top 
and surround the condenser tube. 
OpERATION.—Place 100 cc. of the turpentine and several small pieces of pumice 
(or glass) in the distilling flask, fit the thermometer so that the top of the mercury 
bulb is level with the bottom of the side tube, and the 175° C. (347° F.) mark is below 
the cork. Place the flask in position on the asbestos board or oil bath and connect 
with the condenser. Apply the heat cautiously at first, and, when distillation begins, 
regulate the heat so that the turpentine distills at the rate of not less than 4 nor more 
- than 5 cc. per minute (approximately two drops per second). The initial boiling point 
is the thermometer reading at the instant when the first drop falls from the end of 
the condenser. Discontinue distillation when the temperature reaches 170.0° C. 
(338° F.), or an equivalent thereof, depending on the atmospheric pressure, as out- 
lined below; let the condenser drain and read the percentage distilled. 
The percentage distilled below successive selected temperatures and the tem- 
perature at which each successive 10 cc. distills may also be determined, if desired, 
making the necessary correction of the temperature for variations in ane 
pressure. 
CORRECTION FOR VARIATION IN ATMOSPHERIC PRESSURE.—Since distillation results 
are comparable only when obtained under exactly the same pressure conditions, 
turpentine shall be distilled at that pressure which, at room temperature, 1s equivalent 
to a pressure of 760 mm. of mercury at 0° C. Whenever the atmospheric pressure 
after correcting to 0° C. is other than 760 mm., a correction must be made. Since 
alteration of the pressure in the distilling system requires rather complicated 
apparatus, it is simpler to alter the temperature observation points to comeeneny to 
the prevailing pressure. 
To determine what the atmospheric pressure at the prevailing room temperature, 
or at the temperature of the barometer, would be at 0° C., read the barometer and 
thermometer alongside when about to begin distillation. Refer to Table 9, page 4 
Under the column nearest the observed pressure reading, and on the fine ae 
the observed temperature of the barometer will be found the correction which must 
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