B & L Transplant Surgery - a Tale of Two Refractometers

[ebenbildmicroscopy]

It was the best of times, it was the worst of times... it was the epic of belief, it was the epic of incredulity...

Well, probably 10 years ago, I bought this beautiful old Bausch and Lomb refractometer from Duke University. Back then, I began taking it apart out in the repair shop in order to clean and regrease it. I now recall, back then, being impressed with how clean the thing was and how nice the paint finish was - speculating that it was probably due to the small scratch (see middle pic) on the lower portion of the sample cell. Another refractometer came up on Fleabay last month for nearly nothing, so I decided to take the plunge and finally finish this project with a sample cell "transplant"...

I think my original is actually in better shape than the "new" donor. At any rate, I'm amazed at the resilience of some of the components on these units. Lucite was used as "light piping" throughout the system and, despite being probably 50 years old, is intact and clear - just needs buffing out. I'm going to replace all the seals in the sample cell and thermometer water cooler components.

As is usually the case when resurrecting and restoring vintage microscopes, the worst problems with these two units were the result of users who didn't leave them clean - just wipe the sample cells out after use would have helped. I NEVER understand this phenomena!

[Hobbyst46]

Amazing job!

Does this refractometer include an integral light source or rely on an external Sodium lamp?

BTW, how clear is the field of view (green/yellow circle and scales) ?

I had the opportunity to revive and use an old Zeiss refractometer, and had to improvise a yellow LED (590-595nm wavelength) since the original external Sodium lamp had disappeared to the world of shadows...

[ebenbildmicroscopy]

Hello Hobbyst46!

THANK YOU for the compliment! These refractometers differ (in application) from what you describe in that they measure how an unknown sample influences the angle of refraction of white (visible) light entering the sample. An example would be the common bottle of Cargille immersion oil that you use with your microscope immersion objectives - most immersion oil is supplied with a glass applicator stick attached to the cap - look very carefully in the bottle and you WILL NOT be able to see the glass applicator because, it has the same "refractive index" as the glass, hence the reason you use it with immersion objectives. The immersion oil creates an environment where there is a continuous interface all the way from the sample to the objective lens of your scope. These refractometers measure the amount of angle that the light diverts when encountering the sample...

Having said all that, what you describe is a spectrometer that measures the emission spectra of an unknown - I envy your experience with the spectrometer and hope to eventually do some work in that area! THANKS for sharing your experience - you ought to do a post about it!

[Hobbyst46]

... These refractometers differ (in application) from what you describe in that they measure how an unknown sample influences the angle of refraction of white (visible) light entering the sample. An example would be the common bottle of Cargille immersion oil that you use with your microscope immersion objectives - most immersion oil is supplied with a glass applicator stick attached to the cap - look very carefully in the bottle and you WILL NOT be able to see the glass applicator because, it has the same "refractive index" as the glass, hence the reason you use it with immersion objectives. The immersion oil creates an environment where there is a continuous interface all the way from the sample to the objective lens of your scope. These refractometers measure the amount of angle that the light diverts when encountering the sample...

Having said all that, what you describe is a spectrometer that measures the emission spectra of an unknown - I envy your experience with the spectrometer and hope to eventually do some work in that area! THANKS for sharing your experience - you ought to do a post about it!

Sorry for the misunderstanding. No, I referred to a refractometer, not a spectrometer which is a totally different instrument. A refractometer is used to measure the refractive index of a material - chemicals, oils, brewery products, sugar solutions, salt solutions, crystals, fuel, and many more. Since the refractive index always depends on the wavelength of light, to be meaningful, it must be defined at a standard wavelength. Here a citation from the Cargille web site:

"The refractive index of immersion oil is specified at one wavelength, generally the mercury e line (5461 A) because this wavelength is near the middle of the visible spectrum where the eye has the greatest sensitivity. The e line is specified by DIN /ISO; however, there are still some immersion oils calibrated at the sodium D line (5893 A) and the helium d line (5876 A). DIN/ISO specify that the refractive index of general purpose immersion oil at the e line at 23 C shall be 1.5180 +/- 0.0004 (DIN), +/- .0005 (ISO)."

I am used to the refractive index being designated "nD" (n sub D), D means the 589nm of the sodium spectrum. The indices of commercial immersion oils (Cargille, Fluka, etc) are known. But, to identify an unknown liquid, or verify the nD of any liquid, I place a drop of it on the refractometer prism, cover with the mobile window, turn on the sodium lamp, rotate a knob until the dark and bright parts of the FOV are clearly visible and identical in size (the scheme is shown in the manual), and read the refractive index (nD) directly from the scale. I can compare the reading to a table of known nDs of materials to identify my unknown. For example, some time ago I prepared a home-brew diatom mountant by mixing styrofoam and cinnamon bark oil. Checked its nD in a refractometer to verify it was between 1.55 and 1.60 - logical, in between the known nDs of the components.

The citation above from the Cargille brochure tells me that their n's are specified mostly at 546nm (green) and not the 589nm (yellow) - this important information is new to me.

And, about the oil applicator in the Cargille oil bottle - here is a funny demonstration: Hold the bottle against a halogen lamp, and the tip disappears exactly as you said. Hold it against the whitish light background of the LCD monitor of the computer (when it displays the Microbehunter Forum posts ) and the tip is visible, although faintly! worth trying, for fun! but it demonstrates the importance of the wavelength. Does it mean that the immersion oil is most effective (between the slide and objective and condenser) under halogen light, rather than LED light ? I'm not sure...

[ebenbildmicroscopy]

Hello again, Hobbyst46!

I stand corrected and learn something new everyday! I so closely associate the sodium light source as an emission source comparison, I've just got that in my head as the only scenario. I think I have that Cargille publication and this is another one that makes for interesting reading, promoting use of the microscope and a set of refractive standards to determine index of materials being compared under magnification.

Your description lead me to go pull this out of the archives - I had forgotten I had it!

[Hobbyst46]

Likewise, I learn a lot owing to this great forum.

This link was posted about 9 months ago by MicroBob (citation):
"Here the measuring of the refractive index of mounting media is described in german: http://www.mikrohamburg.de/Tips/T_Brechungsindizes.html"

I guess there is more about this in the Cargille booklet.

[Scarodactyl]

Just as a general question, what type of materials are these b&l refractometers meant for?

[ebenbildmicroscopy]

Hello Scarodactyl!

Most refractometers are intended to measure the angle of refraction of liquids, however these B&L units are more of a research instrument and can be used to measure index in even, uniform opaque materials. For use in my hobby microscopy lab, this is clearly over-kill. When I was in college, I worked in the laboratory of the late mycologist, James F. Wilson who specialized in studying non-mating types in Neurospora crassa (orange bread mold) produced from micro-injection. When the crosses would alternate generations to form ascospores, we would isolate them and store them in a sugar solution that could be maintained in "suspended animation" in a dessicator cabinet for years. Suspension in a sugar solution of a specific refraction (ie, a specific concentration) seemed to work best (although, at what index, I have looooong forgotten).

I will be using this B&L to identify the index some glass chips against a set of standards in order to identify the type of glass.
JeffO

[Scarodactyl]

Cool. I am mostly interested in refractometers for gemological work. I have a couple of the basic models and they work just fine, but I have occasionally wondered if a B&L would work for the purpose, and if so if it would work better. The issue being that a lot of industrial refractometers are meant for water solutions and have a limited range that doesn't extend to the higher RI of gems. This sounds like it might be worth checking out. I saw one at a surplus store in New York earlier this year and didn't buy it, kinda regretting that now. To be fair I didn't know what it was.

[ebenbildmicroscopy]

hello again, Scarodactyl... here's a link to the manual for that particular refractometer, the Bausch and Lomb Abbe 3L...

I hope it gives you a more thorough explanation as to suiting your application:

https://vademecummicroscope.files.wordp ... imized.pdf