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 T u b e
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).
