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Weight of water


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I've been assigned a new task at the pottery shop: mixing casting slip. As I'm making 20 gallons a day I'm using plastic buckets to measure water. I tested several buckets and noticed they all differ, slightly, in what they consider "one gallon". I decide to stick with one bucket to keep things consistent.

I then consider measuring deflocculant. There too I notice several different plastic things measure out milliliters/ounces differently. 

So I wonder: does the "weight of water" still hold true that one gram of water, by weight, equals one milliliter of water, by volumn? If this holds true then all of my plastic measuring devices are incorrect. (Only slightly, though, but incorrect nonetheless.)

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This page has a decent table for density variation by temperature:
Water Density | U.S. Geological Survey (usgs.gov)

Other variables to consider might include dissolved material, thermal expansion/contraction of measuring device?
I'm thinking there's another major variable, but can't put my finger on it just now...

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2 minutes ago, Jeff Longtin said:

So I wonder: does the "weight of water" still hold true that one gram of water, by weight, equals one milliliter of water, by volumn?

Sort of, but ...
- The SG of water varies with temperature.
- Dissolved solids will increase the SG (mainly thinking of hard water).

Size of the effects on SG seem small enough to ignore "for government work"

Water - Specific Gravity vs. Temperature

https://www.hillcrestplumbingandheating.com/b/hard-water-vs-soft-water-debate-finally-solved
The Guidelines for Canadian Drinking Water Quality Hardness rank hard to soft by CaCO3 levels. Here are their guidelines:

  • Soft Less than 60 mg/L
  • Medium Hard 60 to 119 mg/L
  • Hard 120 to 179 mg/L
  • Very Hard 180 mg/L or greater

 

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Unless you’re using a really expensive scientifically calibrated measuring device, there can be considerable variation in volume measurements. Not all 500 ml graduated cylinders are made equally. For things like commercial packaging, the acceptable variation is even more so.

If you go by weight, there’s still some variation, but as long as you’re using  tap water to do your mixing, I can’t see it making a huge difference. Even allowing for hard vs soft water,  the variance at 60 C/140F (most people’s highest hot water tank setting), the variable is pretty small. If you do have hard water, I’d be more concerned with any calcium carbonate concentrations affecting deflocculation than water SG differences.

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