Randy,
Today at our club meeting we tried mixing up a specific gravity standard to calibrate members' hydrometers. We used the 2 liter diet coke and measuring cup method. All measured way off by the standard.
We then checked them against the refractometer standard I had previously mixed up using a triple beam balance and graduated cylinder. (We compared the sodium chloride content of 3.65 against table 5 in your article to obtain a SG of 1.026.) All hydrometers were within about .002 by that solution instead of being off by as much as about .008 by the SG standard. This led me to suspect that the 2l diet coke bottle and the 1/4 measuring cup are not as precise as suspected.
I weighed the 2l bottle of water (filled to top) from the diet coke bottle: 2047.8g
I then weighed the salt (Morton iodized) from a 1/4 kitchen measuring cup: 78.9g
The 1 tsp measure came out close enough: 6.0g
Based on those measurements the sodium chloride content of the solution we mixed was actually 3.98 weight %. All the hydrometers were measuring the solution at around 1.030, as expected.
I think the recipes will only work if you have access to an accurate scale +/- graduated cylinder as it appears that diet coke bottles and measuring cups are not as accurately reproduced as suspected.
Allen
Today at our club meeting we tried mixing up a specific gravity standard to calibrate members' hydrometers. We used the 2 liter diet coke and measuring cup method. All measured way off by the standard.
We then checked them against the refractometer standard I had previously mixed up using a triple beam balance and graduated cylinder. (We compared the sodium chloride content of 3.65 against table 5 in your article to obtain a SG of 1.026.) All hydrometers were within about .002 by that solution instead of being off by as much as about .008 by the SG standard. This led me to suspect that the 2l diet coke bottle and the 1/4 measuring cup are not as precise as suspected.
I weighed the 2l bottle of water (filled to top) from the diet coke bottle: 2047.8g
I then weighed the salt (Morton iodized) from a 1/4 kitchen measuring cup: 78.9g
The 1 tsp measure came out close enough: 6.0g
Based on those measurements the sodium chloride content of the solution we mixed was actually 3.98 weight %. All the hydrometers were measuring the solution at around 1.030, as expected.
I think the recipes will only work if you have access to an accurate scale +/- graduated cylinder as it appears that diet coke bottles and measuring cups are not as accurately reproduced as suspected.
Allen
