calibrating refractometers

[rwestoll]

Sorry I have been away and missed this thread, so please bear with me. I'm a bit perplexed by the instructions supplied with my Refractometer. This is a cheapo from Hong Kong (Model RHB 90ATC) and has three scales on it. At the Right Hand side there is a water percentage scale between 12 and 27%.(The one I would like to use). In the centre a 58 - 90% Brix and on the left a 38-43 degree Be, whatever this is.

Questions.....
Is the mark at 78.7 % Brix the calibration point for distilled water? If so I find it very hard to adjust the machine to give a good line at this point using distilled water. It produces a curve, not straight line.

So given a liquid of known refractive index -e.g. Silicon Oil has a refractive index of 1.52045, how does that relate to my Refractometer Scales.

I have tried the Extra Virgin Olive Oil method calibrating at 71.5% Brix, advocated by MJBee and this gives an encouraging 17.5% moisture, with nice clear readings. All frames extracted were at least 3/4 capped but there is a lot of HB about here. So I would prefer to use the Silicon Oil to calibrate if someone on the forum can explain how to convert Refractive Index to Brix.

Thanks in anticipation - Richard

 

[oliver90owner]

From Wiki: One degree Brix is 1 gram of sucrose in 100 grams of solution and represents the strength of the solution as percentage by weight (% w/w) (strictly speaking, by mass). If the solution contains dissolved solids other than pure sucrose, then the °Bx is only approximate the dissolved solid content

The scale you will use is the one on the right.

Distilled water is just water, so the answer to your first question is obviously 'no'.

Refractive indices from robinwooddotcom:
Sugar Solution 30% 1.38
Sugar Solution 80% 1.49

Honey is around the 80% mark. Extrapolation should give a reasonable result for your oil. I would not be that bothered about the absolute value for a mixture of sugars, such as honey.

RAB

Here are some more RI's (same origin): Honey, 17% water content 1.494 Honey, 21% water content 1.484

 

[rwestoll]

RAB, you say "Distilled water is just water, so the answer to your first question is obviously 'no'.". But if the scale only starts at 58% Brix, how can the instrument be calibrated at zero?

I suspect the best way to do it is make up an accurate solution of sugar and distilled water which is above 58%. That should give an accurate bench mark to calibrate against. Is sugar in a bag near enough pure sucrose?

 

[Hivemaker.]

I suspect the best way to do it is make up an accurate solution of sugar and distilled water which is above 58%. That should give an accurate bench mark to calibrate against. Is sugar in a bag near enough pure sucrose?

Why not simply buy a small bottle of the proper refractometer calibration fluid.

 

[m100]

So given a liquid of known refractive index -e.g. Silicon Oil has a refractive index of 1.52045, how does that relate to my Refractometer Scales.

It's off the end of the conversion tables I have - something over 85 Brix

 

[drstitson]

Bx = (((((11758.74*nD -88885.21)*nD +
270177.93)*nD - 413145.80)*nD + 318417.95)*nD -99127.4536)

so answer is 90.98

 

[drex]

Cor blimey. I thought beekeeping was so easy. I shake any unsealed over the frames!
Dr S, could you calculate the force I need to apply, rate of acceleration and deceleration and frequency for me please? I want to get it right.

 

[drstitson]

if you give me the equation!!!!

seriously - isn't google/wikipedia wonderful.

NB i know even the cheapo chinese refractometers have ATC now BUT you will make sure you use sodium light won't you!

 

[raysa]

Just to clear up one point which has been hinted at but not spelt out ... a refractometer with a range useful for honey (such as the models mentioned with 12-27 water%) cannot be calibrated with distilled water. Water is 100% water so obviously way outside the range of the instrument.

 

[oliver90owner]

raysa,

I thought it quite clear that if one gram in 100g of solution is one Brix, zero grams in water will be zero Brix. Not actually sure there will be a real zero Brix (ie it is an imaginary value).

The weight over weight % (from the Wiki quote) is a bit of a give-away as well.

0/100 = 0

But thanks for clearing it up for those unable to follow the post.

Regards, RAB