last process HF acts on SiO2 of the glass, forming H2O and SiF4.
Why cannot HF be kept in glass bottles?

A dilute solution of HF, which is a gas, may be kept in gutta
percha bottles, the anhydrous acid in platinum only; but for the
most part, it is used as soon as made, its chief use being to
etch designs on glass-ware. Glass is also often etched by a blast
of sand (SiO2).

Notice the absence of O in the acids HF, HCI, HBr, HI, and that
each is a gas. HF is the only acid that will dissolve or act
appreciably on glass.

Chapter XVIII.

NITRIC ACID.

85. Preparation. Experiment 52.--To 10 g. KNO3 or NaNO3, in a
flask, add 15 cc. H2SO4. Securely fasten the cork of the d.t., as
HNO3 is likely to loosen it, and pass the other end to the bottom
of a t.t. held deep in a bottle of water (Fig. 26). Apply heat,
and collect 4 or 5 cc.of the liquid. The usual reaction is: KNO3
+ H2SO4 = HKSO4 + HNO3. With greater heat, 2 KNO3 + H2SO4 = K2SO4
+ 2HNO3. Which is most economical of KNO3? Of H2SO4? Instead of a
flask, a t.t. may be used if desired (Fig. 27).

86. Properties and Tests.

Experiment 53.--(1) Note the color of the prepared liquid. (2)
Put a drop on the finger; then wash it off at once. (3) Dip a