1001
V O L U M E 25, N O . 6, J U N E 1 9 5 3 described. Using 0.1 sodium hydroxide and 0.1 X hydrochloric acid with methyl red as an indicator and approximately 0.3 cu. mm. of reagents in each titration, the end points were reproduced with a precision of 1 1 2 parts per thousand. The sensitivity of determination of color changes a t the end point can be increased by the use of suitable colored filters in the vertical illuminator, A , and the use of suitably colored glass for the titration capillary to produce a background contrast. The color change in the capillary tube is easily detected, even with standard concentrations of indicators, as the light passes from A , through the length of liquid, J , to the surface of the mercury column and is then reflected back through the entire column of liquid, giving a depth of color equivalent to that of a column of liquid which may be as long as 4 em. ACKYOWLEDGMEST
The author is indebted t o -4.A. Benedetti-Pichler for his encouragement during a course in chemical microscopy at Elroo!,Iyn College.
The spacing of the scale according to the figures in Table I is shown in the illustration, together with the graph of temperature correctione. From 100 to 105% ethyl alcohol temperature corrections were calculated. First readings in this extrapolated region n-ere determined by the formula:
(2)
where
+
dl, d'. B(t - 60) cubical thermal expansion coefficient of glass. taken as 2.5 X per C. hl, = distance between position of meniscus on hydrometer when immersed in V % ethyl alcohol a t t o F. and graduation corresponding to 90% ethyl alcohol a t 60" F. d = density of T.' % ethyl alcohol at ' f F. (1: B
= =
Alcoholometer Scale beyond 100' for Hydrometers. Rogpei Gilmont, T h e Emil Greiner C 0.. S e i \ l o r k , S . 1. HE
master scale for alcoholometers and correction tables up
Tto 100% ethyl alcohol for temperatures from 50" to 100" F.
are given by the Sational Bureau of Standards (Circ. 19, 6th ed., 1924). Frequently, in working with concentrations of ethyl alcohol in the neighborhood of 1 0 0 ~by o volume and a t temperatures in the neighborhood of 100" F. readings are obtained in exces- of 100% ethyl alcohol. As such solutions do not exist, the specific gravity us. concentration relationship was extrapolated by finite differences. Thus, the differences betn-een tabular values of specific gravity (6Oo/6O0 F.) for corresponding equal increments of per cent ethyl alcohol by volume and successive differences of differences were taken, until constant values were obtained. When the third differences were reached, scattering was too great to permit going further, so these rrere correlated by least squares and made to vary linearly, giving constant fourth differences. From the correlated third differences, values of specific gravity n-ere calculated and extrapolated to 105yoethyl olcohol (Table I). From these values of specific gravity a master scale r r a F calculated bv mCms of the formula:
where T * = per cent ethyl alcohol by volume in rvater solution
S,
=
hFo
=
(standard a t 60" F.) *pecific gravity a t 60")60" F. of T.' % ethyl alcohol solution tiiqtance b e t m e n graduation corresponding to 1- % ?thy1 alcohol a t 60" F. and graduation corresponding to90%ethylalcoholat G O O F .
Ti 90 91
Table I. >laster Scale s L
R
04
0 83382 0 83049 0 82703 0 82730 0.81988
0.0000 0.0797 0.1627 0.2489 0.3389
95 96
0 81602 0 81203
0.4333 0. ,5326 0.6377 0.7495 0.8699
cl2 93
97 98 99
0 80789 0 80360 0 79884
100 101
0.79388 0 . 78830 0.78269 0.2763fi 0 . ,6943 0.78181
102 103 104 105
1.0000 1.1419 1.2978 1.4703 1.6626 1.8777 *
90
95 IO0 OBSERVED % ETHANOL BY VOLUME
T E M P E R A T U R E CORRECTIONS T O READINGS OF ALCOHOLOMETERS (STANDARD AT 6 0 ° F ) B A S E D ON M A S T E R S C A L E
ANALYTICAL CHEMISTRY
1002 Table 11. Observed Temp., F. iO(10"C.) 52 54
Corrections to Be Applied to Readings of Alcoholometers (Standard at 60" F.) 95
96
Observed Per Cent Alcohol b y Voluine 97 98 99 100 101 102 103
.4dd to observed per cent alcohol 1.12 1.06 0.99 0 . 9 3 0.86 0.90 0.85 0.79 0.74 0.70 0 . 6 8 0 . 6 4 0 60 0 . 5 6 0 . 5 4 0.45 0.43 0.40 0.38 0.36 0.23 0.21 0.20 0.19 0.19 Subtract from observed per cent alcohol 0 . 2 3 0 . 2 2 0 . 2 1 0 . 1 9 0.16 0 . 1 4 0.46 0 . 4 4 0.41 0 . 3 9 0 . 3 5 0 . 3 0 0 . 7 0 0 . 6 7 0 . 6 3 0 . 5 9 0 . 5 3 0 47 0 . 9 4 0 90 0 . 8 5 0 . 8 0 0 . 7 2 0 . 6 4
56 58
1.17 0.94 0.72 0.48 0.24
62 64 66 68 (20'C.)
0.24 0.49 0.73 0.98
70 72 74 76 78
1.23 1.19 1 . 1 4 1.49 1 . 4 3 1 . 3 7 1 . 7 5 1 . 6 8 1.61 2.01 1 9 4 1.85 2.28 2 . 2 0 2 . 1 0
1.07 1.30 1.53 1.76 2.00
1.00 1.22 1.43 1.65 1.87
0.92 0.82 1.12 1.00 1.31 1 . 1 8 1.04 1.52 1.37 1.22 1 . 7 2 1 . 5 6 1.31)
80
82 84 86 (3OOC.1 88
2.56 2.84 3.10 3.38 3.66
2.46 2.72 2.96 3.26 3.54
2.35 2.60 2.86 3.13 3.39
2.24 2.48 2.73 2 98 3 24
2.09 2.32 2.56 2.80 3.06
1.93 1.76 1.57 2.14 1.96 1.74 2.37 2.16 1.94 2.60 2.38 2.14 1.87 2.81 2.60 2.34 2.04
00 92 94 96 98
3.94 4.23 4.52 4 82 3.12
3.81 4.10 438 4.67 4.95
3.66 3.93 4.20 4.48 476
3.50 3.76 4.02 4.29 4.55
3.30 3.55 3.80 4.06 4.31
3.07 3.30 3.54 3.78 4.02
100
105
5.42 5.24 5.04 4.82
110 11,5
2.82 3.04 3.26 3.48 3.70
2.54 2.74 2.96 3.1G 3.36
2.22 2.40 2.59 2 79 2.98
4,56 4.27 3.94 4.90 4.54 5.55 5.15 5.78
3.56 4.13 4.70 5.30
3.17 3.68 4.20 4.75
5,92
5.32 5 90
120 12.5 130
Values of R in Formula 2 were computed for several values of alcohol for different temperatures, and were then compared with those given in Table I to obtain corresponding values of V. The difference between the true value and the above value gave the correction for the coriesponding temperature. In this manner the isothermals shown in the chart of correction us. observed reading were extended in the eytrapolated region of 100 to 105%. This correction chart is valid only when used in conjunction with the arbitrary master scale shown w.ith it. Corrections from 95 to 105% ethjl alcohol and from 50" to 13O'F. are tabulated in Table 11.
'I from 95 to 100% ethyl
104
105
fastened to the bottom of the sl~dingplatform, G . When the front cell is in position for reading as shown, the tab pinches the drain tube against the flange, so that the cell may be filled with a sample. A back catch, A , is provided t o engage the lip on the platform handle, B , and hold the platform against the back stop, JI. Raising the platform handle slightly and pulling it forward, allow the sample to drain through the rubber tubing to a waste. These modifications do not interfere with the normal operation of the instrument. The back cell may be used to hold a blank or standard sample and pulled into position if desired. When a microcell is used as shown, a 5/~6-inch hole is drilled through the bottom of the microcell adapter, E, to accommodate the drain tube. If the 23-ml. cells are used, a bushing cut from thin sheet metal and having the same pattern as the bottom of the 23-ml. cell adapter, F , but with a 5/ls-inch hole under the front cell, is placed between the cell adapter and platform. This raises the front cell slightly and provides room a t the bottom for the drain tube connections.
For routine use a cell made from a selected piece of ordinary glass tubing is satisfactory, as the same cell is used for all measurements. The cell shown in the drawing is made from tubing 13 mm. in outside diameter. One end is drawn down to forni 2.73 a tube 3/8 inch long by 3/16 inch in outside diam3.20 eter. The other rnd is cut off to provide a cell 3.65 4 . 1 6 3 50 0.75 inch longer than the ordinary cells and is 4.67 3.94 flared into a funnel measuring 1.25 inches across 5,21 4.42 the top. 5.79 4 . 9 4 For most solutions it has been found advantageous to use cells coated with Desicote [Gilbert, P. T., Science, 114, 637 (1951)]. Such cells drain cleanly, but air bubbles must be guarded against by pouring the samples doxn the side of the funnel. Ordinarily the cell need not be rinsed between samples. Tests were made using two permanganate solutions of different concentrations, which gave widely separated optical density readings. Using Desicote-treated cells, successive readings of a solution of one concentration or alternate rradings of the trro different concentrations checked as closely as the same samples transferred to individual absorption ?ells and read in the usual ninnner.
/7- - - -
-n
ACKNOWLEDGRIEVT
Permission by the E n d Greiner Co. to publish this information is gratefully acknov ledged. Special Absorption Cell for Routine Photometric Determinations (With Adaptation to the Fisher Electrophotometer). Richard W. Blake and Manford K. Patterson, Jr., The Samuel Roberts Noble Foundation, Inc., Ardmore, Okla. cell has been designed which facilitates Essentially it is a cell provided with a funnel top for convenience in filling and an outlet a t the bottom with a rubber tubing and pinchclamp for draining. By this arrangement both the need for handling many individual cells and the factor of variations between cells are eliminated. The diagram shows such a cell, D , as adapted for use in the Fisher Electrophotometer. -41~0 shown are modifications of the instrument which permit closing and opening of the drain tube, J,by the same mechanism which positions the cells for reading. In order to provide passage for the drain tube through the bottom of the instrument, a 0.5 X 1.75 inch slot, I, is cut in the bottom of the cell compartment, C, and a hole, L.is drilled through the bottom panel of the instrument. The back of the slot is not cut out, but is turned up and cut off to form the flange, K . The X 13/16 inch tab, H , which is piece cut off is used to make a
/
21
SPECIAL absorption
A rapid routine photometric readings.
In this laboratory two Fisher Electrophotometers have been modified and used with the special absorption cells as dpscribrd One has been used for more than two gears for routine turbidimetric readings of niicrobiological assay tubes and colorimetric readings for other analyses. Operation of both instruments has been very satisfactory. Cells of this type should be readily adaptable to other instruments. Some work has been done R-ith a Becknian Model DU spectrophotometer with a cell and arrangement for closing and opening the drain tube similar to the method described herein. The cell was made from 10-mm. precision bore square borosilicate glass tubing.
