litmus paper.

Experiment 41.--Burn a little S in a receiver of air containing
10 cc. H2O, and loosely covered, as in the O experiment. Then
shake to dissolve the SO2. H2O + SO2 = H2SO3. Apply test paper.

69. Naming Acids.--Compare formulae H2SO3 and H2SO4. Of two acids
having the same elements, the name of the one with least O, or
negative element, ends in ous, the other in ic. H2SO3 is
sulphurous acid, H2SO4, sulphuric acid. Name H3PO4 and H3PO3;
H3AsO3 and H3ASO4; HNO2 and HNO3.

If there are more than two acids in a series, the prefixes hypo,
less, and per, more, are used. The following is such a series:
HClO, HClO2, HClO3, HClO4.

HClO3 is chloric acid; HClO2, chlorous; HClO, hypochlorous; HClO4
perchloric. Hypo means less of the negative element than ous; per
means more of the negative element than ic. Name: H3PO4 (ic),
H3PO3, H3PO2. Also HBrO (HBrO2 does not exist), HBrO3 (ic),
HBrO4.

What are the three most negative elements? Note their occurrence
in the three strongest and most common acids. Hereafter note the
names and symbols of all the acids you see.

70. What Bases Are.

Experiment 42.--Put a few drops of NH4OH into an evaporating-
dish. Add 5 cc. H2O, and stir. Taste a drop. Dip into it a piece