Mercredi 29 juin 2011

gold during the hot season.

This acid has a sour taste and acts powerfully on vegetable colours.
400. It is used to take out ink spots. It is also one of the best tests of the presence of lime.
Exp. Dissolve some oxalic iir id in pure water and let fall a few drops of it into well water. It' the s-nallest quantity of lime be present there will be loi med a white cloud, whicn being an insoluble oxalate of lime will afterward fall to the bottom of the vessel. .
401. This acid forms with the different bases a set of salts called oxalates.
402. Tartaric acid. This acid is obtained from the Supertartrate of potash (common cream of tartar.) Cream of tartar is the lees of wine purified.
403. The casks in which some kinds of wine are kept become encrusted with a hard substance, tinged with the colouring matter of the wine, and is otherwise impure. This substance is known in commerce by the name'of argol. When this is puiified by solution, filtration, and crystallization, it is called cream, or crystals of tartari From their substance the tartaric acid is procured by'tli? following process.
Exp. Let 100 parts of finely powdered cream of tartar, be intimately mixed with about 30 parts of pulverized chalk. This is best done by grinding them in a mortar and passing the mixture through a sieve. Let the mixture be thrown by spoonfulls into eight or ten parts of boiling water: waiting Cor the cessation of the violent effervescence, which is produced by each addition, before any more is thrown in. If it should appear that the acid is not fully neutralized by the above quantity of chalk, but that the solution reddens litmus paper, more chalk must be added until the paper is not chang ed by it.
By the above operation, the tartaric acid combines with the lime, and an insoluble tartrate of lime is found at the bottom of the vessel. Decant the liquor into another vessel, and having collected the tartrate of lime, wash it three or foar times with cold water. Then to the tartrate of lime thrown into a convenient quantity of water, add strong sulphuric acid, equal in weight to that of the chalk employed. The sulphuric acid combines with the lime and forms a sulphate, which is insoluble in the water, it therefore falls to the bottom of the vessel in the form of a white powder. Let the acid and precipitate remain together twenty-four hours, frequently stirring them, then let the precipitate subside aDd decant the clear liquor, which will contain the tartaric acid in solution, together with some sulphuric acid and a small quantity of sulphate of lime. This is to be evaporated by a gentle heat, now and then decanting' it from one vessel to another to get rid of the sulphate of lime which falls down. Finally, after the solution is eva; orated to rather more than 'a fourth of the original quantity, set it away to crystallize. The crystals will be brown and must be purified by again dissolving them in water, evaporating and crystallizing, and this must be repeated until the crystals are pure, white tartaric acid.
404. In the manufactories of this article, some additional processes are used by which a larg r quantity of the-acid is obtained from the same quantity of materials, than can be obtained by the above process.
405. This acid and the carbonate of soda form the boda powders, of which great quantities are prepared
^forf gold during the hot season.


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Par waiji23 - 3 commentaire(s)le 29 juin 2011

None of the salts called filiates

If muriatic acid be distilled with chromic acid, the former absorbs oxygen from the latter and is converted into chlorine, while the latter, in consequence of the loss of oxygen is converted into an oxide of chrome.
385. The salts formed by the combination of this acid with the different bases, are called rhromates.
386. Molybdic acid. When the metal called Molybdenum is heated in the open air, it combines with a large quantity of oxygen, takes the volatile form and crystallizes in small needle shaped white crystals. This compound of the metal and oxygen possesses acid properties. It is composed of molybdenum 74.5 and oxygen 25.5 to the 100.
387- Molybdous acid is formed, when two parts of the molybdic acid and one of the metal are saturated together in boiling water, then filtered, and the solution evaporated in a slow heat. This acid is in the form of a fine blue powder.
Obs. Both of these acids combine with salifiable bases and form salts.
388. Fluoric acid. This acid is obtained from a mineral called Derbyshire spar, Jluor spar, or more properly fluate of lime. In this substance the fluoric acid is combined with lime, and from whence it may be set free by the intervention of a stronger acid.
Exp. Into a retort of lead, see fig. 31, put some pure white fluor spar in fine powder, and mix it with twice its weight of sulphuric acid. Lu'.e the retort to a receiver of the same metal with clay ; then surround the receiver with a mixture of salt and snow or ice, and apply a moderate heat to the retort, taking care not to melt it. . The fluoric acid will be extricated and pass into the receiver, where it is condensed by the cold into the liquid formOAs. The liquid obtained by the above process is called hydro fluoric acid, because it is mixed with water. The water is ex polled from the sulphuric acid by the heat.
389- This acid has the curious property of corroding glass, in consequence of its strong affinity for the silex .which it contains. It therefore cannot be prepared or kept in glass vessels.
lllrs. If a di up of it be placed on a piece of glass it quickly destroys its polish, and if permitted to remain on it, will eat into it to a considerable depth.
390. This acid acts with great energy on the animal fibre. If a drop of it strikes the hand, it raises a painful, and sometimes occasions deep and dangerous ulcers. It is extremely volatile and emits dense white vapors, which the experimenter must be careful not breathe.
391 The fluoric acid is used for the purpose of etching on glass.
Ilhu. The method of etching designs on glass is as follows. First cover a plate of glass of the size required with beeswax or engravers' varmsh. The bees-wax must be spread over the surface as thin as possible. For this purpose heat the glass ever a lamp, and at the same time rub the wax over its surface; then hold the glass in such a position that the wax will run off. If it is not too hot, enough will remain on to cover the surface. Next draw the design by cutting the wax with a sharp instrument quite down to the glass, so that every line shall leave the surface naked. A large needle or sharp pointed pen-knife does well for this purpose. The etching is done by placing the plate is a horizontal position and pouring on the liquid fluoric acid. Where this cannot be obtained, the etching may be done with the acid in the state of gas. This requires ouly very simple apparatus. Tahe a common tin cup, large enough to include the piece of etching within the circle of its rim. On its bottom place a spoonful of powdered fluor spar, and then pour on
strong sulphuric acid enough to make it into a paste. Next place the glass plate on the cup as a cover, with the etching downwards, and set the cup into a dish of hot water, or holt}, it over the flame of a lamp, taking care not to melt the wax. The fluoric acid in the state of gas will act upon the glass where it is not protected by the wax. In ten or fifteen minutes the heating will be done, when the wax must be rubbed off by etching the glass. In this way figures of any kind, as flowers, faces, names, &c. may be permanently and beautifully done on glass.
None of the salts called filiates are particulary interesting except the filiate of lime, from whence the acid is obtained



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Par waiji23 - 0 commentaire(s)le 29 juin 2011

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