I have been trying to make phthalated gelatin according the following procedure: 1] 8g gelatin in 80ml water at 40C. 2] Adjust PH to 10 with 10% NaOH. 3] Slowly add mix of 0.8g Phthalic Anhydride in 6.4ml Acetone, while at the same time keeping PH at around 10.0 4] After all the mix of step  has been added, wait 10 minutes (while monitoring that PH stays at 10.0). Now to test that I did it correctly I then proceeded to lower the PH to below 3.5 with H2SO4. This should have caused the gelatin to precipitate out of the solution, but it did not. Does anyone know what I have done wrong here?