in this experiment. By simultaneously starting the spectrophotometer chart drive a t the beginning of each addition, the time required for complete mixing was automatically recorded-the time was consistently in the 10- to 12-second range. This represents the time required from the beginning of addition to complete equilibrium within the apparatus. Because the aliquots were larger than one would normally add in practice, this time is probably an upper limit. Independent experiments show that during approximately 6 of the 10 to 12 seconds above, sample was being added. Therefore, if the addition time is cut down by adding smaller incrementa of sample, the total time to reach equilibrium from the beginning of addition will naturally drop. However, even in the extreme case the mixing has been shown to be quite rapid. Buret Bleeding. In operation of the
apparatus, there is the opt.ion of lowering the burets into the solvent for sample addition and then withdrawing or hsving the bureta in constant solvent contact. The latter might prove to be more convenient in some cases; however, it introduces the possibility that the burets might bleed into the solvent during the periods between additions. To determine if this were a serious problem the following experiment was carried out. Chloroform was added to the reaction reservoir. The burets were filled with ethyl benzoate and lowered into the chloroform within the reservoir. The magnetic stirrer and the circulating (pump were then turned on.
No infrared absorption was observed a t the frequency of the strong carbonyl band in ethyl benzoate after 45 minutes of operation. This shows that little or
no bleeding of the burete took place under these conditions. Pumping Rate. The pump handles approximately 0.60 ml. per second of liquids with densities in the neighborhood of one, when the line is not restricted with a thin cell. With a 0.01-cm. IR-4 absorption cell in series with the pump, the rate drops slightly to approximately 0.50 ml. per second. This is still several times the volume of the usual infrared absorption cell. ACKNOWLEDGMENT
The authors emress amreciation to R. Robert Brattah for %e suggc tion which led to the development of this instrument. RECEIVEDfor review May 1, Accepted June 5, 1959.
959.
Dilatometers for Highly Viscous Systems: Recording and Nonrecording Instruments JOHN F. VOEKS and ROBERT A. CRANE Western Division, The Dow Chemical Co., Piffsburg, Colif. ,A dilatometer for studies on highly viscous and chemically reactive systems is described. Two models, a simple and inexpensive nonrecording instrument and a recording model, have been used successfully in these laboratories.
S
time ago, the need arose in these laboratories for a dilatometer suitable for use with highly viscous solutions-i.e., solutions with viscosities up to several thousand poise. The materials of construction had to be inert to peroxides and other reactive components found in polymerizing systems; the dilatometer needed to be equipped with recording instrumentation. The dilatometer of Schulz and Harborth (S,6)waa unsatisfactory because of the presence of mercury which was reactive in the systems studied. OME
NONRECORDING DllATOMElER
Principle of Operation. Although in the final version the dilatometer recorded automatically, early models did not. They did, however, satisfy other requirements and offer obvious advantages of simplicity and low cost to those who have only occasional need for such an instrument (Figure 1). The purpose of this instrument is to 1906
ANALYTICAL CHEMISTRY
separate the viscous material-which in this work is a polymer solution with a viscosity up to several thousand poisefrom a low viscosity liquid in the measuring capillary by a diaphragm, bellows, or piston. Dilatometers with Teflon diaphragms have been used in this laboratory with some success, but the difficulty of obtaining tight glass-toTeflon joints led to the model shown. Instrumentation with diaphragm-type dilatometers is more difficult because of problems associated with conversion of volume changes into proportional electrical signals. Mechanical System. As noted in Figure 1, the piston is made from a 1.5cc. hypodermic syringe. The plunger is sawed off a t both ends and fastened by a graded seal to’the capillary and stopcock assembly. The barrel is sawed off and sealed a t one end to provide a close fitting cap that slides on the outside of the plunger. With this arrangement, a decrease in the volume of reactants in the dilatometer moves the b a m l in a direction to expose a new glass surface. This is important, and is opposite to the result if the reactants are placed inside a normal syringe. The object is to minimize the tendency for the polymerizing solution to penetrate the space between barrel and plunger. This tendency is further re-
duced by a film of Kel-F grease which lubricates the piston and is sufficiently unreactive chemically. The stopcock a t A locks the barrel in position during the filling of the reaction chamber. The measuring capillary and connectin6 spaces are kept full of water so that with A closed, the relative position of barrel and plunger is fixed. Stopcocks B and C merely facilitate filling the reaction chamber, and are in no way essential to the operation of the instrument. For some work, they may be eliminated or replaced by one near the top of the reaction chamber with advantage. Procedure. Fill the measuring capillary and associated spaces with water. Then set the barrel, lightly lubricated with Kel-F, in about the center of its range and close stopcock A . Assemble the dilatometer. Flush the reaction chamber with prepuri6ed nitrogen and fill with the deaerated reaction mixture. Close stopcocks B and C . Open stopcock A and place the assembly in the thermostat. As the reaction mixture is brought to temperature, it expands, causing the barrel to move up the plunger. The initial positioning of the barrel is made to permit this without jamming the barrel a t the end of ita run. Polymerization is accompanied by a decrease in solution volume. If the dilatometer is completely filled with liquid, this volume change is followed
exactly by the modified syringe and may be observed visually by noting the height of the liquid meniscus in the capillary.
problem of providing automatic recording instrumentation was attacked. A linear differential transformer provides an easy method for converting a linear displacement into a mwurable electrical signal (I). In this instrument, the displacement of the sensing core is balanced by a second coil aa shown in the schematic representation of the instrument in Figure 2. The amplifier detects any unbalance between the two core positions and causes the motor to rotate in such a direction that the balancing core is moved until its displacement is equal to that of the sensing core. A somewhat similar application of the linear differential transformer was made by Kelly and Harris
RECORDING DILATOMETER
Principle of Operation. After satisfactory performance of the modified syringe dilatometer was achieved, the
ln
matic Timing and Controls, Inc., catalog numbers 6171,for the 0.25inch displacement servo mechanism, and 6251, for the amplifier. A single turn potentiometer (lo00 ohms) was mounted as an integral part of the shaft which turns the null balancing cam (Figure 2) so that an electrical signal proportional to the balancing transformer core displacement could be obtained. This shaft rotates 3331/1" for a maximum displacement of 0.250 inch for the differential transformer core. No other modifications to the servo balancing system were made. . RECORDER CIRCUITRY.The circuitpy used to permit zero adjustment, span adjustment, and continuous recording of the output of the dilatcmeter is shown
(4).
-
Table 1. Linearity and Calibration Mechanical System. Figure 2 Data for Recording Dilatometer shows a cutaway drawing of the Pist.on output dilatometer assembly which consists of Displacement, Rotation, Recorder a syringe barrel, connecting rod, transInch Degreee Reading former core, and counterbalance. The 0.250 15 7.5 transformer core is held by a set screw 0.240 30 11.7 to the nickel connecting rod, which in 0.230 43 15.0 turn is cemented with Epon resin into 0.220 55 18.4 the bottom of the syringe barrel so that 0.210 67 21.5 any displacement of the syringe barrel 82 25.7 0.200 0 190 95 29.6 results in an equivalent displacement of 108 33.1 0.180 the transformer core. The counter121 37.0 0.170 balance provided to prevent zero drift 0.160 134 40.5 which might occur dur to leakage be148 44.5 0.150 tween the syringe and the barrel under 161 48.0 0.140 the weight of the transformer core has 174 52.0 0.130 been found generally unnecesssry. 0.120 186 55.2 199 59.0 The counterbalance support and other 0.110 0.100 212 62.6 parts necessary to hold the coil of the 225 66.5 0.090 differential transformer to the glass 238 0.080 70.0 parts of the dilatometer are machined 25.~ 1 73 7 0.070 from Lucite. The clamp is held to0.060 264 77.4 gether bv four small bolts, not shown in 0.050 277 81 . O Figure 5. 290 0.040 85 .O Electrical Circuits. BALANCINQ 0.030 304 88.8 316 SYSTEM. The null balance servo 0.020 92.5 0 010 329 95.9 system and amplifier used in this instrument were manufactured by Auto-
19/38 S T A N D A R D T A P E R
PLUNGER
FROM
AND
I I/.kc.
BARREL SYRINGE
OFF
Figure 1. Nonrecording dilatometer
RUN I
1OO-X SPAN P O T . FRONT PANEL
+ --,
-PULLEY
SUPPORT
1.5-VOLT
I
CELL
CLAMP
2
FRONT
/ CAM)
TANDARD TAPER GLASS J O I N T
)
\
O
T
\,
$
? RECORDER
BALANCING MOTOR
IK
i/ Figure 2.
PANEL
RECORDER INPUT
"d\ P
.,\
REPrATING SLlDIWlRE 2 CALl0RATlON NETWORK
Schematic of recording dilatometer
SLIDEWli)E
( DRIVEN BY SERVO
Figure 3.
SFAFT)
Calibration network
VOL 31, NO. 1 1, NOVEMBER 1959
1907
Table II. Calibration of Recording Dilatometer with Water
Specific
Recorder
1.01207 1.01162 1.01116 1.01072 1.01028 1.00985 1.00943 1 . m 1
5.8 18.9 32.7 45.2 58.1 70.1 81.6 93.9
1.01162 1.01116 1.01072 1.01028 1.00985 1.00943 1. m 1 1.OO861
13.6 27.3 39.8 52.3 64.5 76.1 87.9 99.1
To,C. Volume of W a W
Reading
The recorder presently used is a portable one manufactured by Varian ABLW ciatea and requires 10 mv. for full-scale displacement (Model G-11A). Any similar recorder could be used as well. CAUBRATION
Kl.0 49.0 48.0 47.0
46.0 45.0 44.0 43.0
Run 2 49.0 48.0 47.0 46.0 45.0
44.0 43.0 42.0 Data taken from reference (3).
in Figure 3. This circuitry permits accurate adjustment of recorder span tg correspond always to a given displacement of the syringe barrel placement. The recorder zero adjustment permits setting the start of a run a t zero on the recorder chart regardless of the actual initial position of the syringe barrel. These two adjustmenta, zero and span, are not completely independent, but no dficulty is encountered in bringing both to the desired settings.
OF INSTRUMENT
Teats were made to check the output of the null balancing system to determine whether it accurately indicated displacement of the syringe barrel. The results are presented in Table I. The figures in column 1 represent the physical displacement of the syringe barrel from an arbitrary zero position. This displacement was measured by a dial indicator graduated in divisions of one thousandth of an inch. Column 2 gives the angular displacement of the potentiometer shaft. Column 3 gives the recorder reading corresponding to these displacements. These data have been fit by least squares to a straight line giving a value of 368.8 divisions per inch displacement. Given the above value for chart divisions per inch of displacement and the diameter of the syringe plunger (0.3368 inch in this instrument), the number of chart divisions per unit change in volume in the reaction chamber is readily calculated. For this ins&ment, the value 253 chart units per cc. was obtained. This method of palibration has proved easier than methods bawd on the volume of the dilatometer
bulb and the known temperature coefficients of specific volumes of various liquids, such aa water. Two examples of the latter method are given in Table 11, however. They serve to illustrate the quality of results which may be expected. The calibration constants calculated by least squares from these two runs were 246 and 250 scale divisions per cc. change in volume. These are in’good agreement with themselves and with the value 253 estimated above, Both runs were made with a dilatometer bulb which contains 116.0 cc. when the barrel of the syringe is in its uppermost position. The instrume‘nt accurately records changes in volume ‘of the dilatometer contents. LITERATURE CITED
(1) Automatic Temperature Control Co., Philadelphia, Pa., Bulletin R-31,“Differential Transformers aa Applied to
the Measurement of Straight Line Motions.” (2) Burnett, G. M., Trans. Faraday Soc.
46,772 (1950). (3) “Handbook of Chemistry and PhyaICE,” Chemical Rubber CO., 38th ed., 19561957 p. 1990. (4) Kelly, d. J., Harris, H. M., J . Am. Ceram. SOC.39, 344-8 (1956). (5) Schulz, G. V., Harborth, G., Angm. Chem. 59,W (1947).
RECEIVEDfor review March 23, 1959. Accepted June 22,1959.
Rapid Determination of Blood Alcohol by Diffusion Oxidation in High Vacuum H. S. MAHAL Forensic Science laboratory, Bombay 8, India
bA
new simple, quick, and accurate procedure for estimations of blood alcohol has proved very useful in this laboratory. An analysis was done in 5 minutes with 0.5 ml. of blood. Recovery of alcohol was very good from blood having alcohol ranging from 0.01 to 0.50 gram per 100 ml. Apparatus and reagents used are readily available in all chemical laboratories, This procedure was not specific for ethyl alcohol, as other volatile reducing substances-e.g., methyl and propyl alcohol, ether, chloroform, and formaldehyde, if present, interfered with the estimation. Acetone, however, did not interfere, and volatile acids were fixed and did not diffuse while carrying out the test.
1908
ANALYTICAL CHEMlSTRY
Q
UANTITATIVE removal and oxida-
tion of ~1~0401 in blood are carried out in a minute by diffusion oxidation in high vacuum. The quantity of dichromate used in the oxidizing difTusate is determined by iodometric titration. Volatile acids and free acetone in blood do not interfere with the test. With the introduction of complete prohibition in the state of Bombay, this laboratory has been concerned with thousands of determinations of alcohol in blood samples for liquor consumption cases each year. Because the courts in these cases depend on the blood alcohol concentration, it became imperative to have a rapid and axurate microtest that could be applied for routine multiple analyses.
Numerous micro- and macromethods have been described for the quantitative determination of alcohol in biological fluids. Most of these methods are based on Widmark’s method (6)which utilizes oxidation of the separated alcohol by acid,dichromate solutions; an alkaline permanganate solution had also been tried as an oxidizing agent (a,but was generally abandoned. Alcohol has been separated from blood by distillation and by aeration or diffusion desiccation a t room or higher temperatures ( I , 2 ) . Some of these methods, no& withstanding their lack in specificity as compared to enzymatic procedures (4), have been generally favored for routine multiple analyses. A special committee of the British Medical Association on the
