Organic Combustion Apparatus for Highly Volatile and for Inflammable Liquids JOHANNES H. BRUUN AND W. B. MASON FAULCONER, Sun Oil Company Research Laboratory, Norwood, Pa. BU8BLE
FIGURE1.
I
PD -ASWEST05
ORGANIC COMBUSTION
is transferred carefully into the vaporizing tube (Figure 2) which has been cooled in advance by immersing it in a proper cooling agent. As soon as a sufficient cooling of the liquid in the sample tube has been effected, the capillary tip of the glass tube is broken off by means of any suitable breaking ch as the one shown in Figure 3, and the combustion r to control the evaporation of the low-boiling substance from the vaporizing tube into the combustion tube, the temperature of the cooling mixture in the Dewar flask should be maintained well below the boiling point of the sample. By gradually lowering the Dewar flask, a steady and uniform evaporation of the liquid may be a c c o m p l i s h e d in about 15 minutes. In working with liquid mixtures such as lower boiling petroleum fractions, motor fuels, etc., a brownish residue is frequently found in the sample tube when the vaporization of the lowboiling liquid has been completed. In order to complete the combustion of this residue, the Dewar flask is replaced with the electric heater shown in Figure 2, after which the temperature of the lower part of the vaporizing tube is increased to a dull red heat. The electric heater may also be used for controlling the evaporation and the rate of combustion when higher boiling liquids (boiling point above 70" C.) are being analyzed. Here it is advisable to heat the small copper spiral between the vaporizing tube and the rubber stopper to a dull red heat by surrounding a small section of the tube with an electric heating coil. Organic combustions of highly inflammable liquids, such as low-boiling petroleum fractions, are preferably carried out in an atmosphere consisting of a mixture of nitrogen and oxygen as indicated in Figure 1. - I n order to avoid explosions the amount of oxygen in such cases is increased from about 40 per cent by volume a t the beginning of the combustion to 100 per cent a t the end of the combustion. The apparatus shown in Figure 1 has been in use for over 3 years, during which time organic combustions have been
APPARATUS
N ESTABLISHING the purity of low-boiling hydrocar-
bons, such as propane, the carbon-hydrogen ratio may be used as a convenient supplement to other criteria such as freezing point, boiling point, molecular weight, etc. For this purpose organic combustion analyses of the greatest possible accuracy are essential, and special precautions are necessary in order to avoid explosions which are likely to occur whenever the concentration of the inflammable vapor in the combustion tube becomes large enough to reach the explosion limit with oxygen or with the oxygen-nitrogen mixture, when used. In principle the combustion apparatus used is identical to that published by Reid (2) and is shown in Figure 1. As indicated in Figure 2, a controlled evaporation of the sample is accomplished by attaching to the combustion tube a separate vaporizing tube made of quartz. The dead space a t the bottom of the vaporizing tube enables the operator to evaporate the sample a t a low rate, even in a rapid stream of oxygen. Thus, a gas mixture well below the explosion limit is ensured in the combustion tube and the secondary oxygen or air is obviously eliminated. The samples to be analyzed are cooled and inclosed in sealed Pyrex glass tubes which have been drawn out into a fine capillary opening a t one end. In sealing this open end with the oxygen flame, all hazards are APORlZlNG removed if a stream of nitrogen is directed toward the tip of the cooled glass tube while the flame is being applied. Considerable pressure will d e v e 1o p within the glass bulbs in which low-boiling samples are sealed when they are allowed to warm up to room temperature. However, such low-boiling liquids as propane (boiling point -42.2' C.) have been kept in this manner in a desiccator for weeks without the occurrence of a single breakage. When the sample tube is ready it FIGURE2. VAPORIZING TUBE 315
PRESS
HERE
WREAK
TIP
TUBE
FURNACE
STEEL
TUBE
STEEL
WIRE
F I G U R E3 . D E V I C E FOR BREAKING TIPSOF SAMPLE TUBES
INDUSTRIAL AND ENGINEERING CHEMISTRY
316
TABLEI. RESULTS OF THE COMBUSTIONS
Sample
Run
Hydrogen Carbon Deviation Deviation from mean from mean Found value Found value
% Commercial propane fraction (oontains propylene)
,
1 2
3
Cracked petroleum fraction (boiling between 25' and 50' C.)
1 2
n-Heptane
1
17.64 17.68 17.65 Bv. 17.66 14.37 14.41 -4v. 14.39
% -0.02 +0.02
-0.01
....
-0.02
+o.oz
....
16.01 -0.05 2 16.09 +0.03 3 16.09 +0.03 Av. 16.06 Theoretical 16.10
.... ... .
% 82.22
82.26 82.20 82.24 84.82 84.78 84.80
Carbon-Hydrogen Ratio Deviation from mean Found value
Sum
% -0.02 f0.02
-0.04
.. . .
+0,02 -0.02
....
83.76 -0.08 83.87 +0.03 83.89 f0.05 83.84 .. 83.90 ..
.. ..
made of a very great number of low-boiling petroleum fractions without the occurrence of a single explosion. The data shown in Table I indicate that the results can be duplicated with an accuracy of about 0.05 per cent, even if rubber stoppers are used a t both ends of the combustion tube.
Glass Head for a Laboratory Water Still PAUL F. SHARP AND EARLE B. STRUBLE Cornel1 University, Ithaca, N. Y.
T
WO large Pyrex flasks, joined by a goose neck of widebore glass tubing, have been used for large-scale laboratory vacuum distillations in various laboratories for a number of years. In this laboratory two 23-liter flasks are used, one serving as the distilling flask, the other as the condenser, with the cooling water flowing over the outside. Difficulty with the repeated loosening of the tubes in the head of laboratory water stills, which permitted a trace of the cooling water to enter the stream of distilled water, led to the trial of a Pyrex flask as a stillhead. A 5-liter flask was used on a steam-heated still with a capacity of 8 liters (2 gallons) an hour. The glass stillhead was satisfactory and has been in almost daily use for about 2 years.
81
+CON DENSING WA TER
99.86 99.94 99.85 99.88
4.66 fO.01 4.65 0.00 4.65 0.00
99.19 99.19 99.19
5.90 f 0 . 0 1 5.88 -0.01 5.89
99.77 99.96 99.98 99.90
5.23 +O.Ol 5.21 -0.01 5.21 -0.01 5.22 ... . 5.21 . ..
...
..
...,
.... .
VOL. 8, NO. 4
For greater accuracy all rubber connections in Figure i should be e l h i nated and replaced with ground glassto-glass, glaes-to-copper, or quartz-toquartz joints (1). If a separate combustion tube is used for the analysis of liquids only, it is evident that, since the usual combustion boat has been the ing tube and the combustion tube may be made in one piece, thereby eliminating the rubber stopper between them' In such case the section of the combustion tube which is normally used for the boat and for the copper spiralmay be either entirely omitted or filled with copper oxide. Literature Cited
(1) Bruun, J. H . , Bur. Standards J. Research, 2, 487 (1929). (2) Reid! E. E.1 J. Am. Chem. SOc.134,1037 (1912). RECEIVED May 9, 1934. Resubmitted April 22, 1936.
A Simple Micro- and Macro-Kjeldahl Steam Distillation Apparatus J. M. FIFE U. S. Department of Agriculture, Bureau of Plant Industry Division of Sugar Plant Investigations, Riverside, Calif.
T
HE Kjeldahl distillation apparatus shown in Figure 1
possesses all the advantages of the apparatus now on the market and yet is so much simpler in design that it can be built by the average laboratory technician without difficulty and a t a comparatively low cost. B y placing a steam chamber, C, between the steam g e n e r a t o r , B, and the distilling chamber, F , the s t e a m jacket and its two large ring seals are eliminated, which is the chief difficulty encountered by the ordinary laboratory technician. The distillation is carried out with all s t o p c o c k s closed. The generated FIGURE1 steam passes through the steam chamber, C, to the distilling chamber and then through the trap, G, to the cooled condenser. The water formed from the first steam which condenses in the steam chamber keeps the large 4-mm. stopcock cool and out of contact with the steam. With suction applied at I by means of the aspirator, the sample is removed and ammonia-free rinse water drawn up the condenser tube through the trap, G, and down into the distilling chamber, through the steam chamber, C, and into the sink.
l
The arrangement used is illustrated in sufficient detail to make its construction clear. The curved neck and the return of a small amount of the condensed water reduce entrainment. The transparency of the condenser permits the inspection of its operation. The condensing surface is large. The cooling water cannot enter the distilled water supply. The condenser can be readily cleaned. RBCBIVED February 17, 1936.
RECEIVED January 15, 1936.
