This document specifies
a) a method for determining the hydrolytic resistance of glass grains at 121 °C. The resistance is 
measured and expressed by the volume of acid required for titration of the alkali extracted from 
the unit mass of glass, and can also be expressed by the amount of sodium oxide equivalent to this 
volume of acid, and
b) a classification of glass according to the hydrolytic resistance determined by the method of this 
document.
This document is intended for use on the more resistant types of glass, e.g. borosilicate glass. 
NOTE 1 For the less resistant glasses, e.g. soda-lime, the method specified in ISO 719 is more suited.
NOTE 2 It is emphasized that there is no exact correlation between the classification laid down in this document 
and that laid down in ISO 719, and it is, therefore, essential to identify which classification is being used.rd edition 2020-09 Glass — Hydrolytic resistance of glass grains at 121 °C — Method of test and classification Verre — Résistance hydrolytique du verre en grains à 121 °C — Méthode d'essai et classification Reference number ISO 720:2020(E) ？ ISO 2020 ISO 720:2020(E) COPYRIGHT PROTECTED DOCUMENT ？ ISO 2020 All rights reserved. Unless otherwise specifi