141
V O L U M E 27, NO. 1, J A N U A R Y 1 9 5 5 of visual matching the chromaticity coordinates, x and y, based on the Interns,tional Commission on Illumination standard observer and coordinate system ($), were calculated. The method of ten selected coordinates (6)and Standard Illuminant C were used. For the reduced molybdophosphate, values of z and y were 0.153 and 0,200, respectively; for the visually matched color standard, 0.149 and 0.190. These figures show that the solutions match well in color hue. With the aid of the Maxwell triangle ( 4 ) to indicate hue deficiency, an even closer match probably could be obtained by s slight empirical adjustment of solution pH. The stability of the color standards is demonstrated by the data of Table 11. Spectral transmittancy curve^ were determined periodically on a mixture of 4.98 mg. of copper sulfate and 0.920 mg. of bromophenol blue in 10 ml. of acetate buffer of pH 4.53 during the time i t remained in an east window exposed to considerable direct morning sunlight. There was no change in the absorption spectrum of the mixture even after 24 day& indicating that the color standards have good stability characteristics.
The calor standards should prove valuable for routine u8e in the visual estimation of traces of phosphate by the molybdenum blue method. LITERATURE CITED
Deniphs. BuU. SOC. p h m . Bordeazlz. 65, 107 (1027). (2) Florentin, Ann. china. anal. et china. appl., 3,205 (1921). (3) Mellon, M. G.. “Andlytioal Absorption Spectroscopy,” p. 522, New York. John Wiley & Sons. 1950. (4)Ibid., p. 525. (5) Ibid.. p. 535. (6) Meyer, Science. 7’2, 174 (1030). (7) Parry. E. P., and MoClellmd, A. L.. Piogressive Fish CdLrrist. 16, No. 4, 158 (1054). (8) Woods, J. T., and Mellon. M. G., IND.END.CHEM.,ANA,,.Eo.. 13, 760 (1941). (1)
R~.OEIYBD for review July 6, 1954. Accepted September 27. 1954. This investigation was supported by Federal Aid to Fish Restoration Funds under Dingell-lohnson Project No. F-3-R.
Method for Sparking Thin Sheet Samples for Spectrographic Analysis Application to Manganese and Niobium Determination in Stainless Steel F. P. LANDIS and L.
P.
PEPKOWITZ
Knolls Atomic Power Laboratory, General Electric Ce., Schenectady, N. Y.
.4 technique has heen developed for sparking thin sheets of steel a n d applied to the spectrographic determination of manganese and niobium. The sample is a n l e d by helium d u r i n g sparking.
A
TECHNIQUE has been developed for sparking thin sheets
of steel for the spectrographic determination of manganese and niobium. Normally, reproducibility and accuracy are achieved by using massive samples which do not become appre-
ciably warmer than room temperature when sparked. However, when thin sheets of stainless steel are sparked, the heat produced by the spark is sufficient to cause oxidation of the sheet on the unsparked side. Whenever this evidence of overheating occurs,
manganese and niobium values are very erratic and unusually high, manganese being affected much more than niobium. It is believed that, because of the high local temperatures of the steel, excessive volatilization of manganese and niobium occurs (with respect to the amount of iron volatilized). An attempt to cool the sample while sparking by attaching it to a solid block of steel or copper was unsuccessful, probably because of the poor thermal contact of the thin sample with the cooling block. More successful was the technique of using a flow of cooled helium on the upper or unsparked side of the sample during the analyBis. Helium was chosen because of its high thermal conductivity. To accomplish helium cooling, the clamp on the Petrey stand sample holder wa8 replaced with a hollow fitting into which the cooled gas could flaw and impinge on the upper surface of the thin sample (Figure 1). The gas was passed through a flom-meter and then through a copper coil immersed in an ice bath and from there into thc Petrey stand clamp. Ice was used a8 a cooling
Table 1. Effect of Variation in Coolant Flow He Flow LiterdMih.
0
4
Anparent
% Mn 0.76 1.09 1.98
28
Figure 1. Apparatus
1.73
2.75
1.38
0.95 0.92 0.93 0.99
i.oo
0.79 0.74 0.74 0.70
15
0.61 0.95
2.80
1.15 1.17 9
Apparent 7% N b
0.68
0.71 0.70 0.71 0.61 0.67 0.60
0.61 0.63 0.53
0.60
0.57 0.62 0.58
0.54 0.53
0.60
0.49
0.55
0.51
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 to
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 to 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 apparatus to measure Reid sapor pressure of small samples consists of a sample cup to fix the liquidvapor ratio 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 method t h a n by standard methods, and less bench space is required. The precision i s as good as that of standard 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.
HE 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.
