Hydrometer error.

[DrD]

Evening all.

First, am I correct in assuming that the specific gravity of pure water should be 1.000 (i.e. that the hydrometer is calibrated using pure water as a reference)?

If so, am I also correct in assuming that my hydrometer reading 1.004 rather than 1.000 in tap water at 20.02 C (calibrated at 20 C) is a result of slight calibration error of the hydrometer, rather than mineral content etc in the tap water?

I'm sure it is irrelevant in practice, but instrument error is a bit of a pet hate and until I can check it in the lab on Monday I'd still like to know.

Cheers :hmm:

 

[winnywood]

If your reading is 1004 at 20°c and your hydro states 20°c then I think it is out of calibration. But be sure you are reading it correctly first before condemning it or applying a correction factor.

 

[oldbloke]

Some are intended to be read at the liquid level, some at the top of the meniscus - would that fix it?
Some have the scale slip inside the shaft, so readings are always off by a fixed amount.

 

[DrD]

Cheers both.

Some are intended to be read at the liquid level, some at the top of the meniscus - would that fix it?
Some have the scale slip inside the shaft, so readings are always off by a fixed amount.

Reading from the top of the meniscus would improve it, but this one is supposed to be read at liquid level and I'd rather not use the meniscus level as that depends on surface tension, which is altered by sugar/ethanol in solution.

I'll try it on distilled water, but it looks like I'm going to need to take the adjustment into consideration, which experience suggests will just annoy me until I buy a new one. This was a cheap Wilko jobby, are there brand makes?


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