Document ZknoVNkxQzZqz6VNJ0jEDLrL

** 148 t Monsanto Chemical Company W. G. KRUMMRICH PLANT LABORATORY ATE ISSUED 9/27/57 WRITTEN BY PAGE NUMBER 1 OF 4 11,784 APPROVED BY STANDARD ANALYTICAL METHOD RLM ATTACHMENTS WGK Drawing No PRODUCT General Method No. 28 TEST Refractive Index by Abbe Refractometer RFS 146 and 147 THIS FORM [ ] SUPERSEDES METHOD 1----- , [X| REVISES INSTRUCTIONS ISSUED ON 10/7Av5 ---------- 1 1 SCOPE This method determines the refractive indices of liquids, and could be modified for use with solids. EQUIPMENT a. Abbe Refractometer, Bausch and Lomb Cat. No. 35-45-50-01. b. Bath, constant temperature and circulator, Fisher Scientific Co. Cat. No. 13-983* Precision Scientific Co. Cat. No. 6600, or equivalent. c. Auxiliary water bath, a Sears and Roebuck ice chest, or equivalent. Solder two eight inch pieces of l/4" copper tubing into the end of the ice chest, about 9 or 9-l/2 inches from the bottom. These are for circulating the water. Solder a third eight inch piece of l/4" copper tubing into the back of the chest about 9 to 9-1/2 inches from the bottom. This is an overflow. d. Circulating pump, Fisher Scientific Co. Cat. No. 13-874-92, or equivalent. e. Approximately 9 feet of red rubber tubing, I.D. 3/8", wall size 3/32", Fisher Scientific Co. Cat. No. 14-166, used to connect ice chest to circulating pump and constant temper ature bath. f. 1 ft. of thick wall rubber tubing, I.D. 3/8", wall size l/8", Fisher Scientific Co. Cat. No. 14-167, used to connect cir- ' culating pump exit to return water inlet of the auxiliary water bath. (See attached drawing No. 147 for assembly) g. Illuminator, Fluorescent, Bausch and Lomb Cat. No. 31-33-55-01, or equivalent. DSW 551056 STLCOPCB4089473 Product: General Method No. 28 Test: Refractive Index Method No. 11,784 Page 2 of 4 pages SAFETY i Consult the specific method for hazards connected with the material being analyzed. DETERMINATION 1. Study the attached drawings to familiarize yourself with the principal parts of the Abbe refractometer which are referred to throughout this method. 2. If the temperature of the water in the auxiliary water bath is above 25C. or the temperature at which the determination is to be made, add ice until the temperature is below that point. , j5- Turn on the circulating pump and the constant temperature bath by flipping the toggle switch marked "Line" to the up position. NOTE: If the circulating pump stays on for over 1 minute, add more ice to the water bath. 4. Holding the refractometer base with your left hand, rotate the telescope with your right hand so it is pointing slightly away from you. 5- Wait until the temperature of the prisms adjusts to 25 .1C., or other specified temperature. NOTE: If the temperature of the prisms does not adjust to 25 . 1C., or other specified temperature, an adjustment is required. In the WGK Laboratory, this adjustment is to be made by the in : strument man. The adjustment is made by rotating the mercroid ' switch (see attached drawing No. 147) to the left to raise the bath temperature and to the right to lower it. 6. Flush the prisms with acetone or other solvent as stated in the specific method for the material being analyzed, wipe the metal holder with tissue and allow the prisms to air dry. (See paragraph b of the Discussion Section) IMPORTANT: The Abbe prisms are made of a dense glass which scratches easily. Do not touch the surface of the prisms with tissue paper or your hands. 7 Place enough distilled water on the lower prism to completely cover it with a thin layer. DSVi 551057 STLCOPCB4089474 Product: General Method No. 28 Test: Refractive Index Method No. 11,784 Page 3 of 4 pages IMPORTANT: Do not touch the prism with medicine droppers or other hard objects which would scratch or nick the surface. ,8. Immediately bring the prisms together and fasten them with the sample compartment lock nut. 9. Holding the refractometer base with your left hand, rotate the telescope with your right hand until the telescope is in a convenient position for observation. 10. Make sure the "Prism Box Shutter" is in an upright position, thus closing the rear ground glass window. 11. Turn on the illuminator and adjust the mirror until light is reflected into the lower prism. NOTE: If a Bausch and Lomb Illuminator is used, it is necessary to depress the red button several seconds before releasing, or the light will not go on. . 12. Release the "Hand Positioning Control Clamp" and move the index arm slowly by hand until the boundary between the dark and light field is under the telescope. 13. Clamp the index arm in this position by means of the "Hand Positioning Control Clamp". 14. Adjust the eyepiece of the telescope up or down until the cross-wires are in good focus. 15. Turn the "Compensator Control Knob" until the color fringe is eliminated, and the dividing line is sharp. NOTE: The line will be sharpest when the edge is just turning blue. 16. Move the mirror slightly. If the dividing line moves, it is a false line. Move the mirror to clear the false dividing line from the field and then locate the true dividing line. 17. Turn the "Fine Adjustment Knob" until the black edge coincides with the intersection of the cross-wires. 18. Adjust the "Scale Magnifier" eyepiece up or down until the refractive index scale is sharply focused. 19. Read the scale where the fine wire crosses it, estimating the fourth decimal place. DSW 551058 STLCOPCB4089475 Product: General $jtori&fQS Test: Refractive Index Method No. 11,784 Page 4 of 4 pages 20. If the reading of the distilled water at 25C. varies from 1.5525, record the difference. NOTE: Corrections at temperatures other than 250. can also be made. The nj)2 of the distilled water is 1.5530 and nj)3o of dis tilled water is 1.5320. For the index of refraction of water at other temperatures consult Lange's Handbook of Chemistry, Ninth Ed., p. 1382. 21. Repeat steps 6 thru l8, substituting the sample for the dis tilled water in step 7* CALCULATION nj)25 = uncorrected reading correction (step 20) Report results to the nearest 0.0001 unit. DISCUSSION a. It is estimated that the precision of this method is 0.0002 refractive index units. b. Although the manufacturer advises against the use of acetone for cleaning the prisms, we have found it more economical to use this method of cleaning. c. The lower prism is used to illuminate and confine the sample, while the upper prism is the actual refracting prism. d. The refractive index depends on the wavelength of the light and on the temperature, which are usually specified with subscripts and superscripts, respectively. Thus nj)25 in dicates a refractive index (n) taken with the monochromatic yellow D light of the sodium arc at a temperature of 25Co e. Although a white light source is used with the Abbe refractometer, the refractive index is obtained for the sodium D line, i.e. 5893A, because the Compensator (Amici) prisms are constructed so that rays from the sodium D line are not deviated, while all other wave lengths are. REFERENCES a. Bausch and Lomb, Abbe Refractometer, Directions for Use. b. Daniels, et al, Experimental Physical Chemistry, 4th Ed., 1949, pp. 14-19 and 5bb. c. Lange, Handbook of Chemistry, Ninth Ed., p. 1382. DSW 551059 STLCOPCB4089476 to {v4lJclffN^ \\tosia AuiTifirimta--*i GonltfoL C.LamP AtdbtfwtNf KN6 yfiftje Cotofirtultia CiDnllftoL KMo& (tilDBElsA Sort SUuTfeft (jRCdUTjON Ifl VlRbM CdnsTahT tt/ftPEtoltfAE &frf \jbwat ft ism DRAWING wn. 146 DSW 551060 STLCOPCB4089477 f I s <c CQ i CC Cafct. CL * V- S3 's in Z 3 o O* cQ n 3 or DS\N 551061 STLCOPCB4089478