I afterwards distilled 100 grs. of the yellow oxyde of iron, mixed with 200 grs. of sulphate of ammonia. Pure ammonia first came over, and afterwards some sulphureous acid. When the retort began to melt. I removed it, and found the iron chiefly in the state of red oxyde, or colcothar, mixed with some sulphate of iron. When oxyde of zinc was used, the residuum was sulphate of zinc. Minium, when triturated with sulphate of ammonia, immediately decomposed it like lime, or the alkalies, and when distilled, the retort contained sulphate of lead. When native green oxyde of copper was distilled, with sulphate of ammonia, the residuum was partly red oxyde of copper, with some sulphate of the same. But the ammonia came over in a concrete state, by reason of the carbonic acid contained in the green oxyde. The oxydes therefore of iron, zinc, lead, and copper decompose the sulphate of ammonia by combining with the acid. I next mixed it with the yellow tungstic acid; but after the distillation, I found the tungstic acid unchanged, excepting that it had acquired a tinge of palegreen. The ammonia and the sulphureous acid also came over in the same manner as when only the sulphate of ammonia was distilled. Lastly, I distilled 1 oz. of the sulphate of ammonia with 20 grs. of the yellow molybdic acid. During the distillation, the ammonia and sulphureous acid were produced in as great quantities as when the sulphate of ammonia was distilled by itself. But the molybdic acid remained in the retort, deprived of oxygen, in the form of a black blistered matter, which was again converted into the yellow acid when distilled with nitric acid. From these experiments it appears, that the sulphate of ammonia is, not, as many eminent chemists have imagined, incapable of being decomposed without some intermediate substance, but on the contrary, the whole of it can be raised and a great part decomposed, whenever a proper degree of heat is applied; for then a certain portion of ammonia first comes over, so that the remainder is combined with acid in excess, and the hydrogen of the ammonia which remains. unites with part of the oxygen of the sulphuric acid, and forms water, which passes into the receiver, accompanied by the acid, now become sulphureous acid, and by the azote in the state of gas. Various methods have long been in use to decompose ammonia. Metallic oxydes produce this effect; and Scheele par ticularly mentions, that if arseniate of ammonia is distilled, gas is produced, and the acid of arsenic is reduced to the metallic form, and as such is sublimed*. appears, a vacuum takes place, occasioned by the alkaline gas, which previously filled the vessels, being neutralized by the sulphureous gas, which is then produced. It is necessary therefore, in about 10 or 15 minutes after the commencement of the operation, that the fire should be raised, and the azotic gas will then soon begin to pass into the jar. Some water will most commonly rush into the receiver, but if the capacity of this is not too small, there will not be time enough for the water to rise sufficiently high, so as to pass into the retort.-Orig. * Essays, page 155. The same effects were also produced when acid of arsenic was sublimed. with muriate of ammonia, p. 161.--Orig. The decomposition of the nitrate of ammonia is also well known, and I have no doubt but that muriate of ammonia suffers a similar decomposition in asmaller degree each time that it is sublimed; for whenever I have had occasion to sublime muriate of ammonia, I have always found some fuming muriatic acid; and from whence could this be produced, but from a portion of the salt which was decomposed during the sublimation. The distillation of the triple salt, composed of molybdic acid, muriatic acid, and ammonia (§ 7 and 9,) places this in a stronger light; for whenever this salt was distilled, a certain portion of molybdæna was left in the retort deprived of oxygen, and muriatic acid was found in the receiver. Moreover, from several repetitions of this experiment, I am well convinced, that by a great number of sublimations the whole of the molybdæna might have been obtained in the proportion that the muriate of ammonia was decomposed. When all these facts are considered, it appears more than probable that most, if not all, of the ammoniacal salts suffer different degrees of decomposition whenever they are treated in the dry way. As the molybdic acid was my principal object, I did not make all the experiments I could have wished on this neutral salt; neither have I as yet exactly determined the proportion of azotic gas produced from a certain quantity. I have found however, that the sublimed undecomposed part of the salt amounted to 183 grs. when an ounce of the salt had been distilled, and that the liquid in the receiver weighed 145 grs.; so that 152 grs. had escaped, which principally consisted of azotic gas, together with some sulphureous acid, and some alkaline gas, which had made their way out of the vessels during the operation. Continuation of the experiments on the molybdate of lead. From the effects which I observed to be produced when sulphate of ammonia was distilled with molybdic acid, I was induced to examine in a similar manner the blue solution B: but first I collected, washed, and dried the pale yellow precipitate which had been formed when the sulphuric solution of the molybdic acid was saturated with ammonia*. This precipitate, when dry, appeared of a deeper yellow, and easily dissolved in muriatic acid. Prussiate of pot-ash was then added to the clear solution, which precipitated the whole of the dissolved matter in the state of Prussian blue. The filtrated solution в was now evaporated till it became a dry concrete salt, the colour of which was pale greyish blue. I collected this salt, and having reduced it to powder, put it into a small glass retort, and having fitted on a receiver, I distilled it in the same manner as was employed with the sulphate of ammonia. The products which came over were also the same; and when the bottom of the retort began to be softened by the heat, I removed it, and found the residuum to be a • Whenever the solution was sufficiently diluted, I always found that ammonia precipitated the iron free from any part of the molybdic acid; but when either of the fixed alkalies were used, a portion of molybdic acid was precipitated with the iron into a state similar to the first portions of those white flocculent precipitates, which have been already mentioned in § 9 and 10.-Orig. black blistered matter. I then examined the sulphureous acid and sulphate of ammonia which had risen, but did not find any trace of molybdæna. I next poured nitric acid diluted with an equal weight of distilled water on the black residuum in the retort, and distilled it. As soon as the acid began to be warm, nitrous fumes were discharged, and when the distillation had been repeated with a 2d portion of nitric acid, I found the whole of the black matter converted into a pale citron-coloured substance, which was the molybdic acid. § 11. Analysis of the molybdate of lead.-I put 250 grs. of the purified ore reduced to a fine powder into a glass matrass, and having poured on it 1 oz. of concentrated sulphuric acid, I digested it in a strong heat during an hour. When the solution was become cool and had settled, the acid was cautiously decanted from the powder, and distilled water was poured on till it came away tasteless. The same operation was repeated twice, so that 3 oz. of sulphuric acid were used. The acid solutions and washings were then filtrated, and were received in a large glass vessel. I diluted the pale blue liquor with distilled water, in the proportion of 16 to 1, and afterwards gradually added ammonia till it was completely saturated. The liquor then became deep blue, and appeared turbid. When it had stood about 24 hours, a loose pale ochry precipitate subsided, and was collected on a filter, the weight of which had been noted*. This precipitate was edulcorated, and afterwards dried with the filter on the flat top of a tin vessel heated by boiling water, after which the weight of the precipitate was 4.2 grs. The colour of the dry precipitate was yellowish brown, and when dissolved in muriatic acid it was precipitated by prussiate of pot-ash in the state of Prussian blue. I now poured part of the clear blue solution, which was composed of sulphuric and molybdic acid saturated with ammonia, into a glass retort, and when about half was evaporated, I continued to add the remainder of the liquor at different times till the whole was become a concrete salt. I then raised the fire and continued the distillation till all the sulphate of ammonia was decomposed or driven over: but as some of the sublimed salt was fixed in the neck of the retort, I turned the bottom of it upwards, and poured some distilled water into the neck, so as to wash out the salt; after this I increased the fire till the whole body of the retort was become red-hot. The residuum in the retort was a black blistered mass, on which I poured 3 oz. of nitric acid diluted with an equal portion of water, and having distilled it, I repeated the operation, and thus converted the whole of the black This is one of the many instances which prove the weak affinity between molybdæna and oxygen; for it is well known that pure ammonia precipitates iron from sulphuric acid, in a state nearly similar to martial æthiops; but in the present case the iron takes a considerable portion of oxygen from the molybdic acid at the moment that the acid menstruum is saturated by the ammonia, and it is therefore precipitated in the form of a yellowish-brown oxyde, while the molybdic acid being thus deprived of so large a quantity of oxygen, is converted into a blue oxyde which remains in solution.-Orig. + To be certain that all of the ammoniacal salt is decomposed, it is absolutely necessary that the retort should he made red-hot.—Orig. matter into the yellowish acid of molybdæna. When the retort was sufficiently cooled, I cut off the neck, and removed the powder, which weighed 95 grs. I next proceeded to decompose the residuum left by the acid solution in the state of sulphate of lead; and having edulcorated it, I boiled it during an hour with 4 oz. of lixivium of carbonate of soda, then washed the powder, and poured on it nitric acid much diluted. The whole was dissolved, excepting a small portion of white powder, which was washed and dried on a filter by the heat of boiling water, and then weighed of a grain. This on examination, proved to be siliceous earth. I then exactly saturated the nitric solution with lixivium of pure or caustic soda, and having washed and dried the precipitate of lead, I exposed it in a porcelain crucible for a of an hour to a heat rather below red; after which it weighed 146 grs. As I had found by a former experiment, that a small portion of iron remained with the lead, I dissolved the 146 grs. in diluted nitric acid, and precipitated the lead by sulphuric acid. The solution was then filtrated, and being saturated with pure ammonia, I obtained a small quantity of oxyde of iron, which, when dried as before, weighed The loss was therefore..... 1. gr. By this analysis, 250 grs. of the ore yielded Oxyde of lead Grs... Oxyde of iron {12}.... and siliceous earth..!.......... Grs. 146 95 5 2 0 7 grs. 246 9 3 1 as annexed, and lost 3.1, which I am inclined to place principally to the account of the lead, as it is scarcely possible to decompose the sulphate of lead without some loss, occasioned by the action of the alkaline solution. § 12. Experiments on the yellow molybdic acid, obtained by the analysis.A. When exposed to the blow-pipe on charcoal, it was melted by the exterior flame, and the sides of the charcoal were covered with small long crystals, which had a metallic lustre resembling silver*. When the heat was continued, the whole was melted, and for the greater part absorbed by the charcoal, the edges of which became covered with a blue powder. When melted in a spoon of platina, some yellow powder was deposited near the edges, and a brownish yellow shining matter was formed, which became streaked in cooling. With borax it produced a brownish-yellow glass, but when the quantity of molybdic acid was small, the colour was sometimes blue when the globule was heated by the interior flame. With soda in the platina spoon it formed a brownish opaque matter. And with phosphate of ammonia and soda it formed a glass, which, in proportion to the quantity of molybdic acid, varied from a greenish blue to a deep blue. B. 10 grs. of the yellow molybdic acid were boiled with 6 oz. of distilled water. About 3 grs. were dissolved, and the solution when filtrated was of a pale yellow * Scheele mentions a similar product obtained when molybdana was exposed to the blow-pipe. Essays, p. 230.-Also by sublimation. Essays, p. 238.-And Mém, sur la Molybd`ne, par M. Pelletier. Journ. de Phys., Dec. 1785, p. 439.-Orig.. colour. It had scarcely any perceptible flavour, but turned litmus paper red. When prussiate of pot-ash was added to a portion of the solution, no apparent change was effected; I therefore added a small quantity of nitric acid, which produced a copious brown precipitate of molybdæna. The sulphuric and muriatic acids had the same effect, when poured into the solution, either before or after the addition of prussiate of pot-ash. With muriate of tin it changed to a beautiful deep blue. Lead was precipitated from solution of nitrate of lead, in the form of a pale yellow precipitate, which was a regenerated molybdate of lead. Nitrate of barytes rendered the solution slightly turbid, but I did not find that the precipitate which subsided was soluble in cold water, as Scheele has mentioned*. The solution did not precipitate lime from nitric acid. c. 10 grs. of the yellow molybdic acid were dissolved when digested with 1 oz. of concentrated sulphuric acid. The solution as it cooled became blue. Prussiate of pot-ash produced a reddish-brown precipitate. Muriate of tin had no effect. When a portion of the solution was distilled to dryness, the yellow molybdic acid was left in its original state. The remainder of the solution was saturated with lixivium of soda, by which the blue colour was heightened, and some white floc-. culent matter was precipitated. Prussiate of pot-ash added to part of this saturated solution did not precipitate the molybdæna, till the alkali was again supersaturated with an acid. Muriate of tin poured into the solution saturated with alkali, changed it to a deep blue; but when the alkali was again saturated with an acid the muriate of tin ceased to have any effect. The white flocculent matter which was precipitated. when the solution was saturated with soda, was edulcorated and heated with nitric acid, by which it was converted into a yellow powder, similar to the molybdic acid which had been dissolved. D. 10 grs. of the yellow molybdic acid, when digested in a strong heat with 1 oz. of concentrated muriatic acid, formed a pale yellowish-green solution. Prussiate of pot-ash precipitated the molybdæna. Muriate of tin had not any effect. A portion of the solution being distilled to dryness, left a greyish-blue residuum.§ I then saturated the remaining part of the solution with lixivium of pot-ash, by which the blue colour became more apparent and a much larger quantity of white flocculent matter was precipitated than when soda was employed. Prussiate of pot-ash did not affect this solution, till the alkali was again saturated with an acid. Muriate of tin was precipitated by the solution saturated with alkali, highly coloured with blue; but when the alkali was again saturated with an acid, the muriate of tin had no Essays, p. 234.-Scheele does not mention the quantity of water which he employed.-Orig. + Scheele observes that sulphuric acid dissolves a considerable quantity of molybdic acid, and that the solution as it cools becomes blue and thick; but when heated, the colour disappears, and returns again as the liquor cools. Essays, p. 235.-Orig. M. Pelletier says, that a small portion of molybdæna is raised by sulphuric acid when distilled with it; but I did not find it so with the molybdic acid.-Mém. sur la Molybdène, Journ. de Phys. Dec. 1785.-Orig. Scheele has made the same observation. Essays, p. 235.-Orig. |