Of the commoner mineral acids the chemical changes of Nitric Acid, from their evident complexity, have formed the subject of numerous memoirs, while those of sulphuric acid, from their assumed simplicity, have been to some degree neglected; on the other hand, the physical properties of the latter have been studied with considerable elaboration, while those of the former have been passed over, doubtless on account of the corrosive nature of the acid and the difficulty of preparing and preserving it in a reasonable degree of purity. Further, with certain exceptions, the alterations in physical properties induced by the products of reduction, be they nitrogen peroxide or nitrous acid, either singly or conjointly, have attracted but little attention, though it is a common matter of observation that the current intensity of a Grove’s or other cell containing nitric acid remains constant, even though the fuming acid, originally colourless or red, has become of a deep green tint. It is more than probable that of the factors of Ohm’s law, both the E. M. F. and internal resistance are continually varying. At the earliest stages of the enquiry it was found that the passage of a few bubbles of nitric oxide gas into a considerable volume of nitric acid produced an alteration of one percent, in the resistance, and the same result could be effected to a less degree by exposure to sunlight, and to a still less degree by exposure to artificial illumination. Therefore, we determined to investigate the alterations of conductivity produced by changes of concentration and temperature in samples of acid purified with necessary precautions, more especially as former workers upon the subject have either used samples of acid confessedly impure, or have been silent as to any method of purification, or have adopted no special care in dealing with a substance so susceptible of polarisation.
The Dissociation of the Compound of Iodine and Thio-urea
