ANALYTICAL CHEMISTRY
142
With the cooling system described, a flow of helium of from 5 to 25 liters per minute, depending upon sample thickness, produced the desired results. I n d l cases, the results were read from working curves that had been prepared using massive standard samples. GiveninTableIaremanganeseandniobiumvaluesdetermined from a sheet of 0.010-inch steel. For this thickness of sample, optimum flow is approlimrttely 28 litersper minute. The apparent values for manganese and niobium are not reduced to the true values of 0.40 and 0.38, butthey do approach minimum, reproducible values. These values must be corrected t o
the true value by a chemical analysis of one piece of each proposed sample thickness from a given heat of steel. Heat identification of large quantities of sheet stock can then be rapidly performed. For a general application of this technique to thin sheet stock of varied manganese and niobuim concentrations, complete working curves based on chemical analyses would have t o be drawn for eac'h sample thickness. 1'he precision of this method is now as good as that obtained h massive samples. . . for the Atomic Energy Commission. Work aarried out under oontrac' NO.W-31.109 En=-52.
Reduced-Scale Aleid Vapor PresSIi r e Apparatus R. L. LETOURNEAU, JULinn
r.
IV~~YJVIY,
and
'W. H. ELLIS
California Research Corp., Richmond, Calif.
A n a p p a r a t u s to measure Reid sapor pressure of small samples consists of a sample cup to fix the liquidvapor r a t i o and a pressure transduoer to conyert the pressure into an electrical equivalent, whioh is m a s ured by an auxiliary detecting circuit. The range is 0 t o 20 pounds. A sample of only 3 ml. is required. The time required to handle a sample properly a n d m a k e a measurement is about one third less by this m e t h o d t h a n by s t a n d a r d methods, and less bench space is required. The precision i s as good as that of s t a n d a r d methods.
in Figure 2, consists of a sample cup tightly clamped to a pressure transducer. A polyethylene gasket, lightly greased, is used to ensure a vapor-tight seal. The transducer element is a full-
ured bv a detector circuit.
The &Dositeside of .the bellows is
T.
H E Reid vapor pressure test is widely used in the petroleum industry as a measure of the vapor pressure of volatile, nonviscous petroleum products. The standard ASTM method ( 1 ) uses a bomb-type apparatus and requires a t least a 5-ounce sample. Although quarter-sized bombs are available, the amount of sample required is still too much to be taken directly a t the carburetor or other parts of the fuel system where only small quantities of fuel are available. Such information is often desirable in studying vapor lock and weathering characteristios of fuels. Therefore, au apparatus to measure Reid vapor pressures on small samples was developed and tested. It differs from apparatus previously reported for this type of measurement
Figure 1. Apparatus
(8).
DESCRIPTION OF APPARATUS
Figure 1is a photograph of the ap sratus with a cell in the oonstant temperature oil bath. The eel?, 8 drawing of which is shown
Table I.
Stability of Reduoed Scale Reid Vapor Pressure Apparatus (Measurements on pure noetone) Date
Operator
Scale
Pre*aure, Lb./Sq. Inch
Hot sir required to dry the vapor space is obtained from a %foot coil of 0.25-inoh stainless steel tubing (not shown) heated hv conneetina each end of the coil to the low voltage side of a 115- to 5-v& transformer. The 115-volt winding-is &orom a Variac. Air is blown directly through the steel tubing. On the outlet side. the steel coil is connected throueh a niece of rubber tubing to a short length of 'jlsinch outer dTamefrr steel tubing which can be inserted inside the pressure transducer. The heat generated and the temperature of the air can be controlled by adjusting the Variac. The scale an the calibrated halmcnce oontrol, Helipot, in the bridge circuit has 1000 divisions. and the bridge can be bdn n c d to T I diviision or ~ 0 . 0 2pound. Thc t~.;ns~Iucrm rere cslil,ratcd npinsc a mercury mnometrr arid are linear u w r tlic 0 to ?O-pounrl range. A typical cnlilrratiun i q qhown i n Ficurr 4. Electrical stability wa8 determined by measuring the vapor pressure of pure acetone. The results %.-e listed in Tahles I and 111. These results show that the stmdard deviation due to factors which include bridge atahility is 0.044 over a period of 2 months, and that stability is not the limiting factor in the repeatability of the method.
V O L U M E 27, NO. 1, J A N U A R Y 1 9 5 5 C A N N O N PLUG
143 utes. The air temperature is such that the temperature in the vapor space of the transducer is as near 100" F. as possible when the sample cell is connected to the transducer. Experiments have shown that a temperature of 102" F. from the air preheater will compensate for the drop that takes place while the cell is being connected. The sample cup is wiped clean and immersed almost to the top in an ice water bath. A piece of absorbent paper or a cork is inserted in the liquid space to prevent moisture from condensing in the cup. To prevent cooling of the air in the vapor space of the transducer and heating of the cup and sample while the apparatus is being assembled, the following sequential steps are carried out as uickly as possible. When the cup has cooled sufficientlv and %e sample is ready to charge, the gasket is coated lightly with vacuum stopcock grease. The sample bottle is inverted and shaken vigorously to mix the liquid and the air. The cup is removed from the ice water bath, the water is wiped off, and the gasket is placed on the top of the cup. The hot air tube is removed from the vapor chamber, the Helipot dial is set a t zero, the potentismeter circuit is adjusted to the null position by means of the 500-ohm zero adjustment in series m-ith the Helipot, and the air jet is replaced to keep the vapor chamber a t the proper temperature. The sample is charged to the chilled cup, the hot air jet is removed, and the cup and transducer are clamped together. After the cell is assembled, it is shaken, upside down, for 30 seconds. The cell is placed in the 100" F. bath in an upright position. After a minimum of 15 minutes, the galvanometer is again brought to null position by use of the Helipot and the dial is read. The Helipot dial reading times a constant factor gives the Reid vapor pressure in pounds.
PRESIURE T R A N S W C C R STATHAM LABORATORICS MODEL P I - Z O G - 8 7 5
4 -CONNECTION
VAPOR SPACE
-LIQUID
Figure 2.
=5
IUL
C U P = I 4ML
Pressure Transducer and Cell Assembly
A 1 -
CALIBRATED B A L I K C ,CONTROL
1
loon
- SOURCE DC
T
IS"
SCALE X 00200: PSI
I
i Figure 3.
+
I.,.
""
/
LINE
.
POWER
Simplified Diagram of Reid Vapor Pressure Indicator
Operation. The method of operation is as nearly the same as t h a t of ASTM D 323-52 as is practical with the reduced scale apparatus. Samples are drawn into chilled containers through a cooling coil if possible. The size of the sample container should be such that it is approximately SO% filled, and stored cold until used. Dewar flasks filled with ice water make convenient baths if the samples are to be stored for only a few hours; otherwise, cold room storage is more convenient. Before the first determination in a series is made, the assembled cell is preheated in the 100' F. constant temperature oil bath for 10 to 15 minutes. The cell is removed from the bath and carefully cleaned. The vapor space in the transducer is flushed with isopentane, the isopentane is removed by suction, and the vapors are blown out by use of the steel tubing connected to the hot air source. Hot air is blown into the transducer for a t least 10 min-
I/
-0
Zbo
4 M
do
M O O
SCALE READING
Table 11. Typical Replicate Measurements of Reid Vapor Pressure of Gasolines on Reduced Scale Apparatus Sample
lox
13X
Date Run 7-28 7-28 7-28 7-29 7-30 7-3 1 7-31 7-31 8-4 8-4 8-5 8-5 8-5 7-28
Operator B B B B
A B
A A B D
D
B B R
Reid Vapor Pressure, Lb./Sq. Inch 7.24 7.46 7.30 7.34 7.66 7.08 7.18 7.66 7.44 7.20 7.26 7.16 7.50 13.62
Figure 4. Calibration of Reid Vapor P r e s s u r e Apparatus
Although the apparatus is not checked against a mercury manometer each time, as in the standard method, the original calibration of the dial is done in this way. A standard sample is run frequently to check the accuracy. This procedure also detects leaks or other difficulties in operation. The new apparatus has one scale to cover the 0 to 20-pound pressure range, eliminating the necessity for three separate gages. The sample storage container can be of any &e larger than 2 ml., and an elaborate transfer procedure is replaced by simply pipetting the sample from a chilled pipet. It is important that the sample be kept cold while it is being transferred from the sample container to the cell. This can be accomplished by using chilled pipets. The ends of the pipet are sealed with rubber policemen while they are being chilled, to prevent internal condensation of moisture; the outside should be wiped dry to keep extraneous moisture out of the sample. If sufficient sample is available nearly to fill a Pounce
ANALYTICAL CHEMISTRY
144
Table 111.
Standard Deviation of Replicate Samples
Sample
h-0. of Observations
Av. Reid Vapor Pressure
Standard Deviation
deviations and replicate results are summarized in Table 111. The vapor pressures of the samples listed in these tables were determined in a random order by various operators over a period of about 2 weeks. The individual samples were identified only by numbers, and the relationship of the samples was unknown to the operators. The smaller samples permitted easier handling and storage than macro samples so that the small scale measurements require about one third less time than the standard measurements. ACKNOWLEDGMENT
Based on all gasoline samples measured. 76 degrees of freedom.
sample bottle, the sample can be transferred to the cup through a wash bottle top in place of the cork. If 10 to 12 ml. of sample are forced through the delivery tube before charging sample to the cup, the system will be cold enough for safe transfer of the sample. Heating the vapor space to 100" F. eliminates the need for correcting for change in air pressure on heating and for change in the vapor pressure of water. This technique also eliminates the necessity for measuring the temperature of the air chamber n.hen the apparatus is assembled. Performance. The repeatability of the method by different operators within one laboratory was evaluated by determining the Reid vapor pressure approximately 100 times. The standard
The authors are indebted to Robert Matteson and V. B. Waithman for the original design of this instrument. They nish to thank V. C. Davis for designing and constructing the bridge and R. K. Stone for his participation in many helpful discussions of this problem. LITERATURE CITED
(1) Am. Soc. Testing Materials, Philadelphia, Pa., "ASThI Standards
on Petroleum Products and Lubricants," Method D 323-53, November 1953. (2) Levin, H., Morrison, A. B., and Reed, C. R., ANAL.CHEM.,22, 188 (1950). (3)
Statham Laboratories, 12401 West Olympic Blvd., Los -4ngeles 64, Calif., Instmment S o t e s , S o . 4, (November 1949).
RECEIVED for review M a y 26, 19.54
Accepted September 9. 1954.
Determination of Boron in Silicates after Ion Exchange Separation HENRY KRAMER U. S. Geological Survey, Claremont, Calif. Existing methods for the determination of boron in silicates are not entirely satisfactory. Separation as the methyl ester is lengthy and frequently erratic. A n accurate and rapid method applicable to glass, mineral, ore, and water samples uses ion exchange to remove interfering cations, and boron is determined titrimetrically in the presence of mannitol, using a pH meter to indicate the end point.
R
ECENTLT Martin and Hayes ( 3 ) have shown that boron can be separated from interfering cations by ion exchange. Their experimental data are restricted to the analysis of steel samples, although their basic data imply wider applications. This investigation confirms the earlier work and tests the method for the determination of boron in silicates. The conventional procedure for the isolation of boron is by distillation a3 the methyl ester. This method was investigated and, as others have found ( 3 , 4),incomplete volatilization was obtained from large amounts of aluminum, and frequently a double distillation was necessary in the presence of both iron and silicon. As such. the method is unwieldy and time-consuming. In this investigation only minor modifications were made in the procedure described by JIartin and Hayes. Boron is brought into solution either by an acid extraction or by fusion, eluted through an ion exchange bed, and determined titrimetrically in the presence of mannitol, using a pH meter to indicate the end point. METHOD
Reagents. Methyl red indicator solution. Concentrated hydrochloric acid. Sodium carbonate, c.P., anhydrous. Sodium hydroxide, standardized 0.055. Sodium hydroxide, 20% weight per volume (carbonate free, prepared from 50% sodium hydroxide).
Mannitol, neutral, boron-free. Amberlite IR 120 (H), analytical grade (exchange capacity of the dry resin is approximately 5 meq. per gram). This material may be regenerated after use by transferring the accumulated resin from a number of determinations to a large glass tube and washing with (1 9 ) hydrochloric acid until the issuing liquid gives a negative test for adsorbed ions. The hydrochloric acid is removed by washing with distilled water. Apparatus. Beckman, Model 2H, line-operated pH meter with saturated calomel and glass electrodes. Preparations of Ion Exchange Column. A borosilicate glass chromatograph tube, 20 X 400 mm., with sealed-in, coarse porosity, fritted disk provided with a small rubber tube extension and screw clamp is used. Fill the tube with water and add the resin slowly as a slurry until a column 10 inches in length is formed. The column should be free of air spaces. Before using, wash the column with 100 ml. of (1 9 ) hydrochloric acid and follow with 50-ml. portions of water until the effluent gives a negative test for chlorides. Solution of Borates. ACID-SOLUBLE BORATES.Keigh a sample containing 10 to 20 mg. of boron oxide into a 125-ml. Erlenmeyer flask. Add 30 ml. of ( 5 25) hydrochloric acid and connect the flask to a reflus condenser. Heat the misture to boiling and reflux slowly for 20 to 25 minutes. After allowing the mixture to cool slightlv, pour 5 ml. of water through the top of the reflux condenser; disconnect the condenser and wash the tip of the condenser carefully with water. Filter the misture while hot through a 9-em. Whatman 41 H filter paper, and wash the residue with hot m.ter to a volume of about 50 ml. ACID-INSOLUBLE BORATES. Keigh a sample containing 10 to 20 mg. of boron oxide (not more than a 1-gram sample) into a platinum crucible, add six times the sample weight of anhydrous sodium carbonate, and, with a platinum stirring rod, mix the sample and flux intimately. Cover the crucible and heat gently for 5 to 10 minutes to expel moisture. Vow gradually increase the heat so that after 5 to 10 minutes more, a liquid melt is formed. When fusion is complete, grasp the crucible with tongs and give i t a rotary motion so as to spread the contents over the sides of the lower half of the crucible, thus expediting subsequent solution. Cool, and place the crucible in a 150-ml. beaker containing 20 ml. of water. Cover the beaker with a watch glass and add concentrated hydrochloric acid down the sides of the beaker until there is an eyress of 1 ml. over the theoretical amount
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