Gage for Preparation of Laboratory Solutions 0.R. MITCHELL Technical Department, Refining Division, Magnolia Petroleum Company, Beaumont, Texas
T
HE use of a 1- or 2-liter volumetric flask for making large quantities of standard solutions up to 19 liters (5 gallons) is somewhat tedious and time-consuming. While clearglass bottles can be calibrated by placing a mark a t the desired point, this method cannot be used for opaque bottles and has the additional disadvantage that the bottle must be level. A bottle gage embodying the float principle is presented in the diagram and furnishes a simple, rapid, and accurate method for making up solutions in large bottles.
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The gage consists of a hollow bulb on the ’ end of a stem, together with a guide and support for the stem. The bulb must be of such Slmsize and shape that it will pass through the mouths and necks of all bottles to be used and a t the same time float in distilled water. The stem support must have enough clearance between it and the guide tube to accommodate all bottles. The gage for 2-, 3-, and 5-gallon bottles used in this laboratory has the following dimensions: Bulb. Length, 5.5 em.; greatest width, 2.3 cm.; volume displacement, 14.0 cc. Stem. Length, 32.0 cm.; diameter, 0.5 cm. Stem Guide. Length, 9.0 cm.; inside diameter, 0.6 cm. Support. Clearance between support and guide, 1.5 em. The gage iis calibrated by measuring the desired quantity of
Di-
distilled water into a bottle of suitable size, placing the gage in position, and making a mark on the stem even with the top of the guide tube. This process is repeated for other quantities and bottles as desired. However, the calibrations for bottles of any given size may be used for all bottles of the same size, provided that they are of approximately the same diameter and height. I n general, to make up a chemical solution the calculated amount of chemical or chemicals is put in the empty bottle, the page is placed in position, and distilled water is added to the proper mark. The solution is mixed well and then standardized, adjustments being made when necessary. Since the gage operates near the center of the solution with respect to the circumference of the bottle, its accuracy is not affected if the bottle is not exactly level. The slight difference between the specific gravity of the unmixed solution and that of distilled water does not materially affect its accuracy. A suitable holder for the gage is made by placing a small piece of cotton in a 500-cc. graduate. ACKNOWLEDGMENT
The author is indebted to J. H. Jordan for making the gage as well as for suggestions concerning details.
and Triethylene Glycols as Manostat Fluids
w.
J. RUNCKEL A N D D. M. OLDROYD Naval Stores Research Division, Bureau of Agricultural and Industrial Chemistry, United States Department
of Agriculture, N e w Orleans, La.
D
EVICES for automatically controlling reduced pressure have numerous laboratory applications. I n carrying out exacting laboratory vacuum distillations involving use of highefficiency fractionating columns of 100 theoretical plates or more and operating a t high reflux ratios (100 to l), it is essential that the column pressure be controlled closely. Even minor fluctuations in pressure will cause serious disturbance of the equilibrium between liquid and vapor carefully established along the entire length of the column. Since such precise fractionations may extend over periods of a month or even more, the pressure control should not only be very precise but also provide trouble-free operations.
means of a vacuum pump controlled by an ordinary mercury manostat. The pump operates only a t infrequent intervals. Fine control of pressure in the column line is achieved by use of the triethylene glycol Hershberg-Huntress-type (8) manostat, an electronic relay (Cenco-Gilson electronic relay obtainable from the Central Scientific Co., Chicago, Ill., Catalog No. 99,780), and a solenoid-operated breather valve (Model K-20-1 obtainable from the General Controls Co., Glendale, Calif.). Surges are minimized by adequate ballast and by insertion of a G e m . (6inch) length of capillary tubing in the breather line. I n practice there is no perceptible fluctuation of the level of the oil gage when the solenoid opens or closes, although slight motion of the manostat fluid is perceptible. The frequency of the audible clicking of the solenoid valve as it opens and closes provides a good guide to the presence of leaks in the system.
I n the laboratory of the Naval Stores Research Division various terpene hydrocarbons are commonly distilled a t a pressure of 20 mm. of mercury. A Palkin-type oil gage ( 4 ) which can be easily read to 0.5 mm. of oil (and, therefore, to approximately 0.03 mm. of mercury) is used, and column pressure is maintained a t 293.0 mm. of oil (corresponding to 20.0 mm. of mercury) to approximately this precision. Five columns are operated from a single “column line” manifold controlled by a triethylene glycol manostat, and individual distillations have been continued for as long as 5 weeks. The same manostat has been in use for over a year without replacement and without requiring any attention other than reset,tin*:. A dual system of pressure control involving an automatically controlled gas leak from the hipher pressure column line to the lower pressure vaciiuni pump line is used. The low pressure pump line is maintained a t approximately 10 mm. of mercury by
According to Hershberg and Huntress (B), a desirable manostat fluid is a Illiquid which will combine electrical conductivity, low density, low vapor pressure, and reasonable viscosity with the property of wetting the manostat wall”. These investigators recommended sulfuric acid of specific gravity 1.71 as a manostat fluid to control a thermionic relay. Acid of this concentration, although superior to ordinary concentrated sulfiiric acid, is not entirely satisfactory, as it is corrosive and hygroscopic and easily becomes fouled with grease from the stopcocks In addition, some electrolysis occurs and the electrodes become pitted. The Cenco-Gilson electronic relay, which is reported to operate on as little as 0.5 microampere, permits the use of a practically
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ANALYTICAL EDITION
January, 1946
Table I. Comparative Properties of Manostat Fluids Specific Gravity Viscosity Boiling Point a t 20’ C . a t 20’ C. a t 760 Mm. Centipozsea C. Mercury 13.56 ( S ) 1.547 (5) 357.9 (3) 80% &SO4 1.7272 (3) 2 0 . 3 (3) 202 ( S ) (at 26O C . ) 75% &SO4 1.6692 (3) 1 4 . 0 ( S ) 182 (9) (at 25O C.) 3 5 . 7 (1) 244.8 ( 1 ) Diethylene glycol 1.1184 (S) Substance
Triethyleneglycol
1.1254 ( 1 )
47.8 (1)
287.3 ( I )
Vapor Pressure a t 2 j 0 C.
Mm. 0 , 0 0 1 8 (5) 0.124 (3)
0 408 ( 3 ) 0.1 (1) (0 1 a t 46O C.) 0.01 ( 1 ) ( 0 , l a t 80’ C.)
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commercially, have been found superior to sulfuric acid for use as manostat fluids. Both these glycols have sufficient electrical conductivity t o operate the Ccnco-Gilson electronic relay, but when they are used with the thermionic relay suggested by Hershberg and Huntress, a drop of concentrated sulfuric acid must be added to provide sufficient conductivity. The significant properties of the substances discussed above as possible manostat fluids are compared in Table I. LITERATURE CITED
(1) Carbide and Carbon Chemicals Corp., New York, “Glycols”,
nonconducting manostat fluid, therefore materially enlarging the field from which a suitable fluid may be selected. Both diethylene glycol and triethglene glycol, which are readily available
A
Booklet 4763,1941. (2) Hershberg, E. B., and Huntress, E. H., IXD.ENG.CHEM.,ANAL. ED.,5,344 (1933). (3) International Critical Tables, McGraw-Hill Book Co.. New York, 1929. (4) Palkin, S., IND.EXG.CHEM.,.INII.. ED.,7, 434 (1936).
Rapid-Filling Capillary Polarimeter Tube
D A N I E L S M I T H AND SHIRLEY A. E H R H A R D T Research Laboratories of Interchemical Corporation, N o w York 19, N. Y.
I
S T H E course of an extended study of the optical rotations of several scarce materials, the limited quantities of sample available necessitated the use of capillary polarimeter tubes. The ordinary polarimeter tubes which are generally used in sugar analysis (1) and are readily available have an inside diameter of about 9 mm. With a tube of t’his bore, it would have been necessary either to reduce the length to a few millimeters or to use extremely dilute solutions. Since the rotation is a function of the length of tube and concentration of the solution, neither alternative was feasible. Compared with the usual 9-mm. diameter tube, the 2-mm. bore tube employed by the authors requires ouly 5% of the solution volume for an equal tube length. Many investigators have employed capillary tubes such as the Fischer microtube ( 2 ) the Naumann tube ( 3 ) or various modifications of them. The filling of small-bore tubes of these types presents definite difficulties. I t is impossible to pour the liquid into the vertically held tube while one of the cover glasses is fastened to the lower end. If any air bubbles are trapped in the course of the filling, it is generally necessary to empty t’he entire sample before attempting to refill free of air bubbles. This difficulty is usually overcome by introducing the solution from a long thin dropper which mill extend to the bottom of the capillary ( 2 ) . Withdrawing the dropper as the liquid enters the tube permits filling with a fair degree of success. However, the fragility of the long dropper and the ever-present danger of losing the sample if the dropper is broken are disadvantages. The “halo” caused by light scattered from the inside walls of small-bore tubes makes it difficult to obtain a well-defined balance of the photometric field. Xaumann (3) overcomes this difficulty by employing black glass capillary tubes with etched inside walls, but admits that proper cleaning of the etched tube is a problem in itself. The authors have reduced this halo effect t o a minimum by limiting the field of the polarimeter. Whcn a diaphragm is mounted in the threaded end cap of the tube nearest the analyzer, with its hole diameter so selected that it’ subtends a smaller angle t o the observer than does the end of the capillary bore nearest the polarizer, the halo is eliminated at the expense of a small reduction in the diameter of the photometric field. In order to obtain satisfactory tubes for their investigation, thc authors have devised a new type of capillary tube by the simple espcdicnt of introducing into an ordinary straight-bore, 100-mm. polarimeter tube a piece of capillary whose outside
diameter makes a rather snug sliding fit (about 0.01-mm. clearance) in t4e inside of the regular tube. These sections of capillary are optically polished on both ends. Their total length is made approximately 0.5 mm. shorter than that of the regular tube, so that the original tube length still remains effective when rotation measurements are made. While using these assembled capillary tubes it became apparent that they can be filled easily, rapidly, and safely by putting the necessary aniount of solution into the large tube and then slowly lowering the capillary into it. The lowering of the capillary displaces the solution, which rises into the bore completely free of bubbles. The solution also rises in the annular space between the tube and the capillary, but this does not interfere, nor does it use much of the solution. For a tube of the dimensions stated, the annular volume is about 0.015 ml. If the solution does not come all the way to the top, when the capillary is lowered in the tube, a small amount may easily be added from a short dropper. In many laboratories it is necessary to have a large number of polarimeter tubes of different bore size to accommodate the various quantities of solutions to be measured on the polarimeter, By means of a series of different-size capillaries which may be readily constructed, a single observation tube may be quickly converted into a capillary tube of the proper bore. Waterjacketed tubes without tubulatures may be similarly converted to capillary tubes, bearing in mind, of course, that the time required for attaining temperature equilibrium will be greatly increased because of the increased thickness of tube wall. SUMMARY
Polarimetric measurements on small amounts of the sample require the use of capillary tubes. As a result of optical rotation studies on several small samples, a rapid-filling capillary polarimeter tube has been developed. For small volumes of solutions, this tube gives the. maximum tube length which is concomitant with a sufficiently large field to permit photometric matching. LITERATURE CITED
Bates, F. J., and associates, Nat. Bur. Standards, Circ. c440,103 (1942).
Fischer, E., Be?., 44, 1, 129 (1911). Kaumann, H., Biochem. Z . , 211,239 (1929).
