The ever-increasing importance of nitrites in medicine, owing to their power as therapeutical agents, and to the scientific work which has been and is being done to elucidate their pharmacology, renders a knowledge as to the precise amount of nitrite a commercial specimen contains of high, importance. For while to most patients a dose of five or six grains of pure, or nearly pure, nitrite of sodium is as large a quantity as they can conveniently bear, we read of twenty and thirty grains of so-called nitrite of sodium having been administered without dangerous or very unpleasant results. In such cases we cannot but conclude the drug was impure, and MacEwan has shown that samples of nitrite of sodium were met with in commerce containing but a decimal percentage of the salt. Many papers have recently appeared on the estimation of nitrite of ethyl in the spirit of nitrous ether, but in this contribution I desire only to consider those methods suitable for the estimation of nitrous acid in its inorganic compounds.