aniket1706 wrote:
USP in it's stimuli article has given the formula for extrapolation of specific gravity at 25°C to 15.56°C as below.

Extrapolation
Calculation:
Extrapolated Value = R U1 – [( R T1 – S) × ( R U1 – R U2 )/( R T1 – R T2 )]
where
R T1 = Upper value of the test range
R T2 = Lower value of the test range
R U1 = Upper value of the unknown range
R U2 = Lower value of the unknown range
S = Experimental value

Example:
Specific Gravity (SG) for Alcohol determined at 25 converted to 15.56
Experimental:

Sample SG = 0.7893 at 25 .
From the table select the 25 and corresponding 15.56 range for your result:
25 (test range)
15.56 (unknown range)

0.7921 0.7986
0.7871 0.7936

R T1 – R T2 = 0.7921– 0.7871 = 0.0050
R U1 – R U2 = 0.7986 – 0.7936 = 0.0050
0.7986 – [(0.7921 – 0.7893) × 0.0050/0.0050] = 0.7958 SG at 15.56°C.

I was referrring to dehydrated alcohol USP spec. when came across this calculation. There are still two questions unanswered.

1. How to calculate the alcohol strength by referring to alcoholometric table?
2. What to do if the specific gravity is below the highest value in the table. Then the above formula does not apply.

I have searches a lot on the net but could not get any suitable answer. Can anyone help????

Can you tell me from where exactly you find this calculation in USP?