@ Marcus... I don't have time to do this right now, but if really interested:
"This method measures the alcohol content by volume of any wine,spirit,or beer,using a hydrometer, giving readings as accurate as an ebulliometer used by commercial wineries. The method is based on the research of Dr. William Honneyman,Ph.D."
1.Measure the SG of the wine you wish to test.We will call this figure SG-1.
2.Measure exactly one pint of the wine (500ml).We will call this the sample.
3.In a enamelled or glass pan,boil the sample down to about half it's original volume.This drives off some of the water,but all of the alcohol,because alcohol boils at a lower temperature than water.The sample now consists of water,residual sugar,colouring matter,acids and proteins-that is,all the non-alcoholic constituents of the wine.
4.With distilled water or rain water,make the boiled-down sample up to exactly a pint again.Tap water is not recommended because,in some areas,it has a considerable dissolved mineral content which could affect your results.
5.Cool the sample down to 60o-F, or what ever temperature your hydrometer is calibrated for.
6.Read the SG of the sample,we will call this reading SG-2.You will find it higher than SG-1 because you have removed the alcohol and replaced it with water.
7.Subtract SG-1 from SG-2. The difference is called the Spirit Indication.
8.Read the alcohol strength from the following table.
Spirit Indication---- Alcohol Strength,% by volume
1.5 ----------------------- 1,0
2-------------------------- <email> -------------------------- 3.4
6-------------------------- 4.1
7-------------------------- 4.9
8-------------------------- 5.6
9-------------------------- 6.4
10------------------------- 7.2
11------------------------- 8.0
12------------------------- 8.8
13------------------------- 9.7
14------------------------- 10.5
15------------------------- 11.4
16------------------------- 12.3
17------------------------- 13.2
18------------------------- 14.1
19------------------------- 15.1
20------------------------- 16.0
21------------------------- 17.0
22------------------------- 18.0
23------------------------- 19.0
24------------------------- 20.0
25------------------------- 21.0
26------------------------- 22.0
As an example:
SG-1 (SG of oraginal wine) = 0.995
SG-2 (SG of sample at stage 6) =1.011
Spirit Indication= 1.011 - 0.995 = 16
Alcohol strength= 12.3 % by volume.