Besides this Sea-salt, Urine contains another Salt of a singular nature, which crystallizes differently from Sea-salt. In this Salt, according to Mr. Marggraff's experiments mentioned on the subject of Phosphorus, is contained the Acid necessary to produce the Phosphorus of Urine. There is reason to think that this Salt is a Sea-salt, disguised by the fat matters with which it combines during its stay in the animal body.
Mr. Boerhaave calls it the Essential Salt of Urine. If you desire to have it by itself, you must evaporate the Urine, with a gentle heat, to the consistence of fresh cream, filter it, and let it stand quiet in a cool place. Crystals will at length shoot therein, and adhere to the sides of the vessel. These crystals are the Salt you want: they are brown and oily. If you desire to have them purer, you must dissolve them in warm water, filter the solution, and set it by to shoot. This operation repeated several times will render them clear and transparent. Mr. Schlosser, a young and very promising Chymist, is the last who hath made any experiments on this curious Salt of Urine. Those who are desirous of a particular account of its properties may consult his dissertation, printed at Leyden in 1753, as well as Mr. Marggraff's excellent Memoirs, printed among those of the Academy of Berlin.
The chief result of Mr. Schlosser's experiments is, first, that this Salt may be obtained from recent Urine, and even in greater quantities than from putrid Urine, and that too in very little time: seeing it crystallizes in twenty-four hours, after due evaporation.
Secondly, that this Salt is a Neutral Ammoniacal Salt, consisting of a Volatile Alkali, (which can never be extracted from it but in a liquid form, like that which is separated from Urine by the addition of Lime); and of an Acid of a very singular nature, the most remarkable property of which is, its being so fixed as to resist the violence of fire, and turn into a sort of glass rather than exhale in vapours. This is that Acid which, according to Mr. Marggraff's experiments, forms the combination of Phosphorus when united with the Phlogiston. The other properties of this singular Acid are the principal objects of Mr. Marggraff's inquiries.
It follows, in the third place, from Mr. Schlosser's experiments, that this Acid, being combined to the point of saturation with a common Volatile Alkali, forms a true, regenerated Salt of Urine; and that, by this union, the nature of the Volatile Alkali is so changed, that it cannot afterwards appear by itself in a concrete form, but is always fluid, like that which is extricated by the additament of lime.
If Fixed Alkalis be mixed with fresh Urine, they immediately separate from it a Volatile Alkali; and, if the mixture be quickly put into an alembic, and distilled, the first liquor that rises is a Volatile Spirit: or else a Volatile Alkali in a concrete form will rise first, provided the Fixed Alkali made use of be not liquid, and the Urine be dephlegmated.
Herein Urine resembles other animal matters: for Fixed Alkalis produce the same effect on them. This affords us good grounds for believing that all animal matters contain a Neutral Salt of an Ammoniacal nature, which the Fixed Alkali decomposes, as it doth all other Ammoniacal Salts. Quick-lime also extricates from Urine a Volatile Alkali, still more quick and pungent than that which is separated by a Fixed Alkali, and which constantly remains liquid without ever putting on a concrete form: and this is another proof of the existence of the Ammoniacal Salt above-mentioned; for quick-lime hath just the same effect on Sal-Ammoniac, as we shall see in its place. Mr. Schlosser's experiments, compared with those now mentioned, seem to shew that the Urine contains several distinct sorts of Ammoniacal Salts.
Of all the liquors which animals afford, Urine putrefies the most easily, and by putrefaction parts with, or forms, the greatest quantity of Volatile Alkali. If it be distilled when putrefied, there comes over first a Spirit impregnated with much Volatile Alkali; then an aqueous liquor, which Van Helmont assures us is a medicine of wonderful efficacy in dissolving the stone in the bladder. When all this water is come over, and the remaining matter is almost dry, there ascends, on increasing the fire, a yellow Oil, together with a Volatile Salt.
After this there remains in the retort a black charred earthy matter, containing a great deal of Sea-salt. If this matter be calcined in the open air, in order to consume its Phlogiston, and be afterwards lixiviated, all the Sea-salt it contains may by this means be easily separated; nothing but its earth being left behind. This caput mortuum contains also the materials proper for forming Kunckel's Phosphorus; and if, instead of calcining it in the open air, it be urged with a violent fire, in close vessels, it will yield a Phosphorus: but then all the precautions recommended on the subject of Phosphorus must be used; and, in particular, the caput mortuum must be lixiviated before it be distilled, in order to free it from part of the Sea-salt contained therein; because too much of that Salt might defeat the operator, by not only melting itself, but melting also the containing vessel during the operation.