laboratory the barytes we require. For this purpose we strongly calcine, in close vessels, 100 parts of sulphate of barytes well mixed with 20 parts of charcoal in powder. After an hour's calcination the crucible is allowed to cool; the residue is separated from it; it is then diluted in water, and a sufficient quantity of nitrie acid, muriatic acid, or acetous acid, is added to it: the mixture is then slightly heated, which liberates a great quantity of sulphuretted hydrogen and carbonic acid, of which we must be upon our guard. When the effervescence ceases, and the reagent paper announces in the liquor a slight excess of acid, we filter and evaporate it, in order to decompose the sulphuretted hydrogen, and to precipitate the sulphur which was held in solution*. The residue is re-dissolved in the least possible quantity of water, and we add to this solution a saturated solution of caustic potash. There is precipitated, even at the moment of mixture, a great quantity of crystals of barytes; the whole is then allowed to settle at the lowest possible temperature for an hour or two: the mother water is then decanted, the crystals are washed with a little distilled water, and dried by pressing them between several sheets of blotting paper, and they are dissolved in the necessary quantity of boiling water the filtered liquor deposits the barytes upon cooling, which by this process is far purer and cheaper than that obtained by decomposing the nitrate of barytes, by exposing it alone to a high temperature. : It must be observed, that we ought to prefer the employment of the muriatic or acetous acid to that of the nitric acid; in the first place, because the first two acids form with barytes, salts more soluble than the nitrate, and the washing is easier in this case: secondly, because in the solution, the nitric acid, on being decomposed, oxygenates a part of the sulphuret of barytes, and there is then a portion of acid lost, and a part of the barytes absorbed by the sulphuric acid which is formed. As to the caustic potash required in this operation, it is * We may more easily obtain the same end by pouring into the liquor some drops of nitrate of copper or lead, by allowing the metallic sulphuret to subside, and by filtering over again, &c. C4 essential essential that it should be prepared with carbonate of potash free from sulphate; we may render it caustic by following the process published by M. Descroizilles in the Annales de Chimie *. I have frequently pursued the methods he points out, and I have done so with inereasing advantages. Observations by one of the Editors of the Annales de Chimie upon the foregoing Article. I have examined the liquor of the flask transmitted by M. Darcet along with his paper. It was more than half filled with small white crystalline lamine; the liquor greened strongly paper coloured with the petals of mallows. I poured sulphuric acid into it in a slight excess; there was formed an abundant precipitate of sulphate of barytes; at no time was there the least smell of acetic acid. After having filtered the liquor in which the precipitate was formed, I evaporated it in a gentle fire in a platina crucible, and it left no traceof neutral salt. There does not remain a doubt, therefore, that the acetate of barytes is radically decomposed by soda.-L. B. G.. IN ล IX. Upon the Preparation of pure Barytes. By M. ROBIQUET †. IN a note inserted in a late number of the Annales de Chimie, upon the decomposition of the acctate of barytes, by means of soda, M. Darcet points out as a more œconomical and more certain process of procuring pure barytes, to decompose any barytic salt, and principally the muriate, by a caustic alkali: I do not think the preference he gives to this process over the generally employed one, namely, the decomposition of the nitrate by heat, is well founded. On considering the matter in an economical point of view, we see that in both cases we must first obtain a soluble salt of barytes; that in the first we cannot employ the liquors șo *Sec Phil. Mag. vol. xxviii. + From Annales de Chimie, tom. Ixii. p. 61. much much concentrated that no barytes remains in solution ; that whatever precaution we may take in the preparation of the caustic alkali by lime, if not during the filtrations, there will always be a portion of it carbonated; consequently, the same quantity will be wanting in the quantity of barytes we ought to obtain: that, besides this, during its precipitation, as we are obliged to shake the liquor, it carbonates a certain quantity of it: that by washing also we experience a real loss; and lastly, that by a new solution in boiling water it carbonates still more of it; it is visible that all these subtractions united leave but a small quantity, while by the decomposition of the nitrate we absolutely obtain the whole quantity of barytes it contains, and which amounts to very near the half of the weight of dry salt; and that besides, this operation is neither difficult nor expensive, when we know how to manage it properly. Now the following are the precautions necessary to ensure success: Fill near two thirds of the crucible with dry and pulverized nitrate; place the crucible with its lid in a common furnace, in a gentle heat, so as merely to melt the salt in its water of crystallization; increase the fire progressively and with caution, on account of the swelling up which latterly takes place: when the mass, which should be then. of a cherry red, lets no more bubbles escape, cover the crucible with an inch or two of charcoal; adapt to the furnace its dome provided with a pipe of gun metal: heat it thus for a quarter of an hour; take the crucible from the fire; break it, and pack up the barytes as quickly as possible. I also treated by this process seven pounds of nitrate, which I had divided into three common crucibles and placed in one furnace: I produced the complete decomposition in two hours, and I obtained three pounds six ounces of pcrfectly pure barytes. But it must be observed, that if the ba rytes is kept too long in the fire after the decomposition of the nitrate, it is carbonated considerably, and it is afterwards completely impossible, whatever heat we employ, to deprive it entirely of carbonic acid. This is the whole difficulty attending my operation. I am therefore of opinion that it is 6 really by means of fire than to follow M. Darcet's proc even supposing that the quantity of barytes was equa cases, what I have demonstrated could not existof the potash I was obliged to employ would have almost double the expense. As to the purity of the a we are obliged to manage the washings carefully, see that the process of M. Darcet merits the prefe this respect; for it is very probable that the baryt obtained should retain a little of the salt contained mother water; and, on the contrary, that extracte the nitrate is extremely pure, if before decomposing take the precaution of calcining it slightly and rediss in order to separate a portion of the iron proceedin the sulphate employed. X. Observations upon the Combination of the fixe with the Oxides of Lead and the Alkalis. By M. F Apothecary at Versailles*. SCHEELE was the first who observed that the water serves as an intermedium, when we treat the fat oils fats by litharge, retains in solution a substance to whi has given the name of sweet principle of oils, because i in fact, a very decided saccharine taste. But, accordi the observation of this illustrious chemist, this water ing also in solution a certain quantity of oxide of lead, we not think that the taste, which suggested to him name of the sweet principle, proceeds from the property sessed by this metal of communicating a saccharine tas most of its combinations? Where experience has dem strated the contrary, would it not be interesting to inq how this principle came to be formed? What are its pro ties? In what state the oil exists after having abandoned principles which should have given rise to it? If this s traction is absolutely indispensable for forming the com * From Annales de Chimie, tom. lxii. p. 25. nat periments which these inquiries would produce, might we not establish the theory of one of the most important operations of pharmacy, and the relations which its results must have with the alkaline soaps? Such are the considerations which led me to the following experiments: I placed in a tubulated bell glass equal parts of olive oil, litharge, and water: I adapted to the orifice of the bell glass a tube inserted into lime water, with a bladder at the orifice to prevent the access of the external air; this bladder was so disposed that I could move a spatula in the interior of the bell glass, in order to keep the matter from sticking to the bottom of the vessel. The mixture having been brought to the boiling point, I saw the oxide of lead successively pass from red to yellow, and from yellow to white. During the time the experiment lasted carbonic acid was almost always liberated. I allowed the apparatus to cool, in order to examine successively the results of this experiment. The water which had served as the intermedium had a strong metallic taste. When placed in contact with yeast at the necessary temperature, I was never able to produce fermentation*. It precipitated evidently by the sulphuric acid and the hydrogenated sulphurets †. I passed sulphuretted hydrogen into it, until no more precipitate was formed; and I filtrated it in order to separate the sulphuret of lead. The filtered liquor had also a very strong saccharine taste; it was evaporated to the consistence of a syrup; the acetate of lead at this moment did not demonstrate the presence of sulphuretted hydrogen. My attempts to ferment it were equally fruitless as before the separation of the oxide of lead: exposed to the air, it strongly attracts its humidity; when I was for a moment led into an error, because I had inadvertently used yeast, which still contained some alcohol, not having been properly washed. † I was convinced by various experiments that it was of no importance whether in the solution of the oxide of lead the fats or oils were rancid or not, although Scheele thinks they should be rancid. In fact, it will be seen in the course of this paper that this circumstance is completely foreign to the solution. projected |