What measures the hydrogen ion level of a solution

PH. In chemistry, pH (/piːˈeɪtʃ/) (potential of hydrogen) is a numeric scale used to specify the acidity or basicity of an aqueous solution. It is approximately the negative of the base 10 logarithm of the molar concentration, measured in units of moles per liter, of hydrogen ions.

The air is going to come out because of the low pressure.

Answer it was we, the the whole people, who formed the union. and we formed it, not to give the blessings of liberty, but to secure them: not to the half of ourselves and the half of our posterity, but to the whole people- women as well as men.