To ascertain if the sulphate of potash and nitrate of ammoniac could be easily separated, I added to a heated saturated solution of sulphate of ammoniac, pulverised nitre, till the decomposition was complete. After this decomposition, the solution contained a slight excess of sulphuric acid, which was combined with lime, and the whole set to evaporate at a temperature below 250°. As soon as the sulphate of potash began to crystalise, the solution was suffered to cool, and then poured off from the crystalised salt, which appeared to contain no nitrate of ammoniac. After a second evaporation and crystalisation, almost the whole of the sulphate appeared to be deposited, and the solution of nitrate of ammoniac was obtained nearly pure: it was evaporated at 212°, and gave fibrous crystals. VII. _Non-existence of Ammoniacal Nitrites._ I attempted in different modes to combine _nitrous_ acids with ammoniac, so as to form the salts which have been supposed to exist, and called _nitrites_ of ammoniac; but without success. I first decomposed a solution of carbonate of ammoniac by dilute olive colored acid; but in this process, though no heat was generated, yet all the nitrous gas appeared to be liberated with the carbonic acid.[75] I then combined a small quantity of nitrous gas, with a solution of nitrate of ammoniac. But after evaporating this solution at 70°-80°, I could not detect the existence of nitrous gas in the solid salt; it was given out during the evaporation and crystalisation, and formed into nitrous acid by the oxygene of the atmosphere. I likewise heated nitrate of ammoniac to different degrees, and partially decomposed it, to ascertain if in any case the acid was phlogisticated by heat: but in no experiment could I detect the existence of _nitrous_ acid in the heated salt, when it had been previously perfectly neutralised. [75] When nitrous gas exists in neutro-saline solutions, they are always colored more or less intensely, from yellow to olive, in proportion to the quantity combined with them. When nitrate of ammoniac, indeed, with excess of nitric acid, is exposed to heat, the superabundant nitric acid becomes phlogisticated, and is then liberated from the salt, which remains neutral.[76] [76] Hence a nitrate of ammoniac with excess of acid, when exposed to heat, first becomes yellow, and then white. We may therefore conclude that nitrous gas has little or no affinity for solid nitrate of ammoniac, and that no substance exists to which the name _nitrite_ of ammoniac can with propriety be applied. VIII. _Of the sources of error in Analysis._ To compare my synthesis of nitrate of ammoniac with analysis, I endeavoured to separate the ammoniac and nitric acid from each other, without decomposition. But in going through the analytical process, I soon discovered that it was impossible to make it accurate, without many collateral laborious experiments on the quantities of ammoniac soluble in water at different temperatures.