The 0.1562 normal hydrochloric acid for testing the strength of solutions used for testing citrus can also be used to check the strength of the 0.1333 normal sodium hydroxide solution used for testing grape maturity.

By means of a volumetric pipette transfer 25.00 milliliters (ml.) of 0.1562 normal hydrochloric acid to the titrating flask. Do not blow out the liquid remaining in the tip of the pipette, but touch the pipette tip to the surface of liquid in the flask to remove the adhering drop.

Add phenolphthalein indicator solution to the titrating flask, and then add the alkali solution to be tested from the burette, agitating the contents of the titrating flask continuously if possible. As the end-point is approached and the indicator color starts to spread through the liquid, add the alkali solution dropwise, swirling the flask to mix the entire contents before adding additional alkali.

The true end-point is a faint but persistent pink color, not a deep red.

The keeping qualities of the 0.1562 N hydrochloric acid standard are excellent when the bottle is kept properly closed to avoid evaporation and out of direct sunlight. Unused titrating solutions should never be returned to the bottle, but discarded to minimize the hazard of contamination. There should be a slight change in normality of the acid in a six-month period. Sodium hydroxide solutions do not keep as well but tend to become weaker as they age. They should be checked with the standard acid as frequently as necessary to assure the operator that their strength is known.