This proved by examina tion of the salt. Other gums similar. A second portion of weak nitric acid, left to stand on the residuum the same length of time, yielded a fresh quantity of oxalate of lime on the addition of ammonia. It required eight portions of diluted nitric acid in succession, completely to free this mucous acid from oxalate of lime. The quantity was each time less however, and the ninth portion showed scarcely any perceptible indication of it. The eight precipitates together amounted to 2.5 gram. [38.6 grs.] It was of importance to ascertain, whether this foreign matter, which had the appearance of oxalate of lime, were in reality this salt. I therefore boiled it with a solution of saturated carbonate of potash, and when the mutual decomposition of the two salts appeared to me complete, I collected on a tilter the portion that had precipitated. This precipitate, not so white as the former calcareous salt, and in coarser powder, dissolved with great effervescence in nitric acid. Its solution, which was acrid to the taste, was not precipitated by ammonia, but very copiously by oxalate of ammonia. The supernatant liquid, which contained an excess of carbonate of potash, was supersaturated by acetic acid, evaporated to dryness, and the residuum treated with alcohol, in order to separate the acetate from the oxalate of potash, which is not soluble in this menstruum. The mixture, being heated a few moments, was filtered, when the acetate of potash passed through with the alcohol, and the oxalate remained behind. The matter insoluble in alcohol was dissolved in distilled water; and a drop of this solution, added to half a spoonful of lime water, threw down a pulverulent precipitate, evidently of oxalate of lime. The same solution yielded by evaporation crystals of oxalate of potash. The experiments I have described leave no doubt of the nature of the calcareous salt, that affects the purity of the mucous acid obtained from gum tragacanth. The same experiments repeated on gum arabic, and on that called in the shops gum of Bassorah, which does not dissolve in water, afforded me nearly the same results. I observed, the appear I observed, that, in proportion as the mucous acid was Alteration in deprived of the oxalate of lime, that rendered it impure, it acquired a more flocculent appearance. ance of the acid. To ascertain, whether the mucous acid obtained from the Mucous acid sugar of milk, in which it was first discovered by Scheele, prepared from sugar of milk, were likewise contaminated with oxalate of lime, I boiled by way of a similar quantity of sugar of milk with eight parts of ni- comparison. tric acid of the same strength as before. The first portions of mucous acid formed I separated by decantation, and added to the residuum a fresh quantity of nitric acid. A second portion of mucous acid was deposited, which, added to the first, made up the weight of 12 gram. [185.3 grs.], or a fifth of that of the sugar of milk employed. 1 remarked, that this mucous acid, after washing, when This appa. diffused in water had as flocculent an appearance as that rently pure. from the gum, when it had been deprived of its oxalate of lime by dilute acid. This led me to presume, that the acid was much purer than that from gum; and my conjecture was soon confirmed by nitric acid having no action on it. This acid could not take up from it the smallest quantity of oxalate of lime in a long continued digestion, for ammonia did not produce the slightest cloud in the supernatant liquid. fectly pure of lime, What besides left no doubt of the perfect purity of the The acid from mucous acid from sugar of milk was its easy and complete gum not per solution in boiling water. This even proves it to be more when freed pure than the mucous acid from gum, after it has been de- from oxalate prived of oxalate of lime by the means mentioned above: for the latter, when boiled with distilled water, leaves an insoluble flocculent matter, amounting to 0:06 of its weight; as it contained which dries into a gray, horny, semitransparent substance, another submuch resembling in appearance the mucous matter, that connects together the particles of animal concretions; though, when thrown on burning coals, it does not emit the anmoniacal and fetid smell of auimal compounds, and yields by calcination carbonate of lime. The very small quantity I obtained did not allow me to make such experiments, as would furnish a more accurate knowledge of the nature of this substance. stance. From the facts that have been mentioned, we may infer, General con Vol. XXVIII-JAN. 1811. 1st, C clusions. Mucous acid from gum con tains mucite , 1st, There is a striking difference between the mucous acid obtained by the action of the nitric acid from gums, and from the sugar of milk. 2dly, This difference consists in the former being always contaminated with a mixture of oxalate of lime, proportional to the lime contained in the gum; while the mucous acid from sugar of milk does not exhibit the least trace of this calcareous salt, and seems to be perfectly pure. 3dly, The mucous acid from gum may be brought to a similar state of purity by a very simple process, which consists, 1st, in removing all the oxalate of lime by repeated digestions in very dilute nitric acid; and, 2dly, in boiling it in water, which dissolves it, without dissolving the flocculent matter, that the nitric acid did not take up. 4thly, The ucous acid from gum, when thus freed from substances foreign to its nature, is exactly similar to that from sugar of milk, possesses all the properties, that characterise this acid, and may be employed with equal advantage in the most delicate experiments, or such as require this acid to be of the utmost purity. Since I wrote the above I have ascertained, that under certain circumstances the mucous acid obtained from gum of lime, when is mixed with mucite of lime, instead of the oxalate I have prepared with mentioned. This happens, when the nitric acid employed diluted nitric acid. Reason of this. is not in a concentrated state, but diluted with water, and the process consequently goes on not rapidly, but slowly. The difference of the results is easily understood. If a weak acid be employed, the mucous acid is at first produced alone; it precipitates with the lime, with which it forms a salt of little solubility; and it may be separated from the mixture previous to the formation of the oxalic acid, which requires the concentration of the nitric. If on the contrary concentrated nitric acid be used, the formation of the two acids, though taking place in succession, is very near in point of time; and it may readily be supposed, that in this case the oxalic acid, in proportion as it is formed, lays hold of the lime in consequence of its great affinity for this earth. I shall add one more fact, that has led me to remark a singular property of the mucous acid, which I purpose to examine more fully. When When a solution of pure mucous acid in boiling water is Mucous acid changed by gently evaporated to dryness, without separating the crys- heat. talline precipitate, that forms during the evaporation; we soon find, as soon as the whole of the liquid is wasted, that the crystals grow yellow, then brown, and are converted into a kind of viscid substance, tenacious, undergoing a sort of fusion, aud acquiring considerable hardness on cooling. in this state. The mucous acid, that has experienced this changé, is Its properties much more sour than usual, infinitely more soluble in water, and wholly soluble in alcohol, so that its properties are in part altered. At first I thought, that I had converted the mucous acid either into the malic, or the tartaric; but the experiments I have made to verify this conjecture do not yet appear to me sufficient, to authorise my advancing any opinion respecting the nature of the change, that takes place in the experiment I have described. III. Chemical Analysis of a Black Sand", from the River Don, in Aberdeenshire; and of a Copper Ore, from Airthrey, in Stirlingshire. By THOMAS THOMSON, M. D. Lecturer on Chemistry, Edinburgh†. the Don, THE specimen, which formed the subject of the first of Black sand on the following analyses, was brought from the banks of the the banks of river Don, about seven years ago, by my friend Mr. James Mill, who at that time resided in Aberdeenshire. By him I was informed, that considerable quantities of it are found in different parts of the bed of that river,-that it is called by the inhabitants iron-sand,-and that they use it for sanding newly written paper. I tried some experiments in the year 1800, in order to ascertain its nature; but was too little skilled at that time, both in mineralogy and practi For an account of a black sand, consisting of a ferriferous ore of titanium, found on the shores of Liguria, and traced to the rock from which it proceeded, see our Journal, vol. XXVI, p. 94. + Trans, of the Royal Soc., of Edinburgh for 1807. mixed with the cal chemistry, to manage an analysis of any considerable difficulty. The black powder is mixed with a good many small, detritus of gra- whitish, reddish, and brownish grains, which, when exanite or gneiss, mined by means of a glass, prove to be pieces of quartz, felspar, and mica. From this it would appear, that the sand of the river Don consists chiefly of the detritus of granite or gneiss. and consisting of two substances, iron-sand and iserine. The iron-sand described. When a magnet is passed over the sand, some of the black grains adhere to it, and are by this means easily obtained separate. But after all that can be attracted by the magnet is removed, the greater part of the black powder still remains. This residue is indeed attracted by a powerful magnet, but so very feebly, that it is uot possible by means of it to separate it from the grains of sand with which it is mixed. Thus we learn, that the black matter consists of two distinct substances; one of which is powerfully attracted by the magnet, the other not. As this second snbstance was obviously specifically heavier than the grains of sand with which it was mixed, I placed a quantity of the powder on an inclined plane, and by exposing it cautiously, and repeatedly, to a jet of water, I succeeded in washing away most of the grains of sand, and thus obtained it in a state of tolerable purity. The first of these minerals we may call iron-sand, and the second iserine, as they belong to mineral species, which oryctognosts have distinguished by these names. The iron-sand is much smaller in quantity than the iserine, and does not exceed one fourth of the mixture at most. Its colour is iron-black. It is in very small angular grains, commonly pretty sharp edged, and sometimes having the shape of imperfect octaed:ons." The surface is ongh; the lustre is feebly glimmering and metallic; the fracture, from the smallness of the grains, could not be aceurately ascertained, but it seemed to be couchoidal. Opake, semihard, brittle, easily reduced to powder. Powder has a grayish black colour; powerfully attracted by the magnet; specific gravity 4-765, Analysis of it. 1. As acids were not found to act upon this mineral, 100 grains of it were reduced to a fine powder, mixed with |