1000
ANALYTICAL CHEMISTRY
indication of significant hygroscopicity. The solubility of the glass fibers was determined by placing two disks, weighing together 37 mg., in a Gooch crucible and slowly percolating through them first water, then 2 F ammonia, and finally 2 F hydrochloric acid. .4bout 100 ml. of each solvent was applied without suction, so that each solvent could act for about 25 minutes. The following losses of weight mere observed: water, 0.13 mg.; ammonia, 0.20 mg.; acid, 0.02 mg. The determination of chloride was selected for a practical test, because highly retentive paper is usually recommended for the filtration of silver chloride, which tends to peptize on vashing. The test was performed by a group of inexperienced operatorsundergraduate students. In spite of the fact that several grades of less suitable glass fiber paper were used, a standard deviation of f.4.5 parts per thousand around the mean of 27 reports was ohtained. This precision is obviously determined by the lack of experience on the part of the experimenters and their pronounced differences in natural aptitude: S170 of the reports stayed within the standard deviation, and five people reported exactly the average, 5.666 grams of chloride per liter. Prejudice need‘not be considered, for the determinations 1Tei-e performed on different unknown dilutions of a standard Polution. ACKYOWLEDGIIEYT
The authors are indebted to the Hartford City Paper Co., Hartford City, Ind., and the Hurlbut Paper Co., South Lee, hiass., for samples of glass fiber papers and permission to report the findings. LITERATURE CITED
(1) Dural, CIBrnent, ANAL.C m v . . 23, 1271 (1961). ( 2 ) O’Leary, M. J., et al., PTOC. Tech. Assoc. P u l p P a p e r Ind., 35, 289 (1952,. (3) Russell, W. W., and Harley, J. H. A , , Jr., IND.ESG. CHEV., .ANAL. ED., 11, 168 (1939).
C oloriscopic Capillary for Titration of Microgram Samples with Color Indicators. Harold Dorf, 1713 54th St., Brooklyn 4, K.Y, Benedetti-Pichler [IsD.ESG. CHEJI.,ANAL.ED., L 17,187 and (1945)]presented a technique for titration of microOSCSLZO
gram samples under the microscope. I t s principal shortcoming lies in the inadequacy of the method for observing indicator colors. The titration capillary described here has been used to overcome this difficulty. h capillary drawn from thermometer tubing, partly filled with mercury, is mounted vertically in the moist chamber in such a manner that color changes in the liquid within the capillary are observed through the microscope with the use of a vertical illuminator and reflection from the mercury meniscus. hiicrogram samples may be titrated with standard concentrations of reagents and indicators, and colorations are readily observed in total volumes of lesq than 0.5 cu. mm. Miuing is obtained by uw of the plunger as suggested by Loscalzo. The capillary, C, has a bore diameter of about 0.2 mm. and a length of about 2 cm. It is placed so that the light used for illumination passes downward through the liquid, strikes the surface of the mercury, and is reflected back through the liquid. Thus, the attainable light path is equivalent to a depth of about 4 cm. of liquid and is comparable to that obtained in macrotitrations. Preparation of Titration Vessel. A 10-cm. length of thermometer capillary tubing, B, of approximately 6-mm. diameter and 1- to 2-mm. bore, is carefully cleaned and dried. I t is then drawn out in the center to an outer diameter of about 1 mm. and a bore of about 0.2 mm., C . The fine capillary thus produced is broken squarely a t a point about 3 cm. from one end of the wider tube and bent into the shape shown in the diagram. A rubber tube is connected t o the wide end of the capillary and air is blown through it while it is briefly immersed in a suitable water repellent (Drifilm or molten paraffin). The coating of repellent formed, 111,confines the liquid within the capillary. The large end of the
tt
capillary is then connected to the plunger devicr. DeKhotinsky cement or other suitable material is applied over the outer surface, end, and a portion of the inner bore of the capillary as shon n in G. A needle is heated and plunged through the hardened cement in the bore of the capillary and then rrithdrawn quickly before it cools, thus producing a fine opening in the cement plug inside the bore. The whole tube is filled with clean, dry mercury by applying suction while the fine tip of the capillary is held under mercury. The plunger device consists of a brass collar, D, threaded internally for about 1 cm. The unthreaded end is counterbored to fit over the capillary tubing. A knurled screw, E, has a stainless steel or Xichrome wire, F , about 0.5 mm. in diameter and 3 cm. long, soldered into its end. A suitable assembly can be adapted from a standard instrument binding post. The brass collar is attached t o the tubing by carefully heating collar and cement and pressing them together until the cement hardens. The capillary and collar are then mounted in a moist chamber, 0, by DeKhotinsky cement or othsr msans in such a way that the axis of the fine capillary, C, is vertical when the chamber is placed on the microscope stage. The xire plunger, F , is then heated and quickly thrust through the needle hole in the cement plug and allowed to cool. The threads of screw E are engaged and manipulation of the screw will cause the mercury column, H , to rise or fall. I shows the air space. Use of Device. The moist chamber with the titration capillary is placed on the mechanical stage, and the tip of the capillary is brought into focus with the ]OK power objective, L. The vertical illuminator is used for all observation of the tip and transmitted light may be used during manipulations. Screw E is advanced until the meniscus of the mercury column, H , appears in focus a t the tip, and is then retracted one turn to create a n air space about 2 to 3 mm. in length. By the use of the micromanipulator, pressure control devicr. and micropipet as described by Loscalzo and Benedetti-Pichler (:Introduction t o the Microtechnique of Inorganic .$nalrsis,” h e w York, John Wiley & Sons, 1942) the tip of a calibrated micropipet, N (coated on the outside with inert water repellent) is brought over the opening of the capillary so that it nearlj touches it. Pressure in the micropipet is increased until a drop forms a t the tip and touches the opening of the capillary tube a t K . By retracting plunger F with one hand and controlling thr pressure on the micropipet with the other, a measured volume of reagent is introduced into J . Indicator may be added to the first reagent or to the standard solution used in the titration or 130th. By manipulation of the mechanical stage or the micromanipulator, contact is broken and transfer of liquid halts. When standard solution is added, F is advanced so that the column of liquid, J , forms a convex meniscus as a t K . This convm meniscus is essential for proper observation of the color of the liquid in the capillary and for introduction of controlled amounts of reagent from the micropipet. By suitable manipulation of the pressure in the micropipet, liquid will flow from the pipet tip into the hemispheric drop a t K a s soon a s they are brought into contact. When contact is interrupted by withdrawal of the piprt, liquid flow ceases immediately. Mixing is accomplished by raiqing and lowering the column of liquid in J four or five times by manipulation of F.
.1 series of five titrations was performed with the capillary
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. Alcoholometer Scale beyond 100' for Hydrometers. Gilmont, T h e Emil Greiner C 0.. S e i \ l o r k , S . 1. HE
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
= =
Rogpei
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 o volume and a t temperaalcohol in the neighborhood of 1 0 0 ~by tures 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
