1758. Reid, trans. Macquer’s Chem., I. 7. A species of Earth absolutely unvitrifiable in its nature.
1778. Pryce, Min. Cornub., 253. The micose clay … is known to be absolutely unvitrifiable.
1879. Cassell’s Techn. Educ., II. 338/2. The alkali … facilitates the vitrification of the earthy particles, which separately are unvitrifiable.
