An instrument for ascertaining the strength of alkalies. The best, perhaps, is a tube graduated into a number of equal parts. Acid of a known specific gravity, diluted with water, and coloured with infusion of litmus, is poured in until a given number of parts is occupied. The alkali to be tried is accurately weighed, and gradually added to the dilute acid, until the original blue of the litmus, reddened by the acid, is restored. The relative quantity of an alkali requisite to neutralize a given portion of acid of uniform strength, is a test of its strength.