litmus paper

A blue litmus paper turns red in acids while a red litmus paper turns blue in basic solutions.

So they are a litmus paper for wider fertility—not a significant driver of Israeli birthrates.

The solution of lead must contain acid; and if by keeping it does not change litmus-paper, acid must be added till it does.

The blue litmus paper became red showing the presence of an acid.

It turns litmus paper red; sometimes very slightly, and occasionally even not at all.

Litmus-paper, indigo blue or other vegetable colours are at once bleached.

Then add enough of the bicarbonate of soda solution till it turns the litmus paper back to blue.