Abbildungen der Seite
PDF
EPUB

of perchlorates of silver and baryta. We next place it in a tubulated retort, and distil with the same apparatus, and with the same precautions as before. The liquor that first distils over being water only, it is to be received in a capsule, and the proper receiver not adapted till, by means of test paper, we are certain that the acid is coming over. In general, the more slowly the process is carried on the less water is retained in the retort, and the greater the density of the acid. Ice placed in the water surrounding the receiver is useful in condensing the acid vapour. The distillation may be carried on till the residue in the retort is nearly dry, taking care not to decompose the perchlorates of silver and baryta, which should remain behind. The perchloric acid thus obtained is quite pure, colourless, and transparent : its density varies from 60° to 65°; it is oleaginous like sulphuric acid. From 500 parts of pure perchlorate of potash, I have obtained 150 parts of concentrated perchloric acid.

In a future communication I shall describe the process for preparing pure perchloric acid in the crystalline form.

MR. W. H. Balman's Process for Obtaining Oxygen Gas. Dated

May, 1842. A MIXTURE of three parts of bichromate of potash and four parts of common sulphuric acid, placed in a capacious retort, and moderately heated, will yield pure oxygen with a rapidity entirely at the command of the operator.

This process is cheaper than that of heating chlorate of potash ; for two parts of bichromate of potash, will produce as much oxygen gas as one of chlorate of potash, whilst the latter is nearly three times the price of the former : moreover, the residue of the first is valuable, and may be reconverted into bichromate of potash. It is also a more convenient process than any previously known, since it may be conducted at so low a temperature that a common retort and lamp will liberate a considerable quantity of oxygen.

On the Preparation of Cyanide of Potasssium. By M. LIEBIG.*

It is well known that one of the best processes of obtaining cyanide of potassium, is that of decomposing the ferrocyanide by heat. Amongst the several objections to this process, is that arising from a great loss of cyanogen, amounting to one third of the whole contained in the salt employed. This salt, which is composed of two atoms of cyanide of potassium, and one atom of cyanide of iron, suffers no change in its first named constituent by the action of the red heat employed in the process : but the latter constituent undergoes decomposition, which results in the formation of carburet of iron, and a liberation of nitrogen. The carburet of iron thus formed,

Annalen der Chime und Pharmacie.

acting like a sponge, absorbs the fused cyanide of potassium; and in order to obtain any portion of it in a pure state, we are obliged to avail ourselves of solvents, generally alcohol. But as cyanide of potassium is endued with certain properties which, in chemical analysis are found to be extremely valuable, I have availed myself of these properties in order to simplify the mode of obtaining it.

If eight parts of ferro-cyanide of potassium be well dried by calcination on a hot iron plate ; and afterwards finely powdered and mixed with three parts of dry carbonate of potash, and the mixture immediately thrown into a Hessian crucible, previously heated to dull redness, and the temperature maintained, the contents will first melt with a rapid disengagement of gas, and assume the appearance of a brown drossy mass. Shortly afterwards, as the mass becomes heated to redness, the dark colour begins to disappear : and by continuing the heat, the fused contents of the crucible assume a clear amber yellow. If, from time to time, a heated glass rod be introduced, and shortly afterwards withdrawn; the matter adhereing to it, when solidified, will, in the first instance, be brown; afterwards yellow; and at the end of the process, the fluid which adheres to the glass rod will be as clear and as colourless as water : and afterwards harden into a brilliant white crystalline mass.

During fusion, brown flakes, which will be observed floating on the fused mass, will ultimately unite into a clear grey spongy form. If the crucible be now removed from the fire, and allowed to cool a little, this grey matter generally sinks to the bottom: and more readily if the whole be agitated by the introduction of the glass rod. When the deposition is complete, the hot melted mass which floats above may easily be decanted into a warm porcelain capsule, without allowing any of the heavy powder to pass with it.

The mass thus separated from the iron will contain two distinct compounds : the cyanide of potassium, and the cyanate of potash; in the proportion of five atoms of the former to one atom of the latter.

During the fusion of the mixture of ferrocyanide of potassium with carbonate of potash, the following changes take place.

In an early part of the fusion, the cyanide of iron belonging to the ferrocyanide of potassium, and the potash belonging to the carbonate of potash, become decomposed, and their constituents form two other compounds : the cyanide of potassium, and the carbonate of protoxide of iron. At a higher temperature the former takes all the oxygen from the latter, and the results are, cyanite of potash and pure metallic iron.

Supposing the mixture to contain two atoms of ferrocyanide of potassium, and two atoms of carbonate of potash, it would be represented by the following formula :Ferrocyanide of Potassium. Carbonate of Potash.

Cy12 Fe, K, + K, 0, ,CO, = Cy12 Fe, Ko 02 ,CO,, and after the fusion we would have, Cyanide of Potassium. Cyanate of Potash. Iron. Carbonic Acid.

Cy1 KG Cy, O, KO Fe, <CO2.

From two atoms of ferrocyanide of potassium, we obtain five atoms of cyanide of potassium : consequently, one-fourth more than by the fusion of that salt alone by a red heat. The small portion of cyanate of potash with which it is mixed will not interfere with any of its uses. The presence of the cyanate is easily detected by the liberation of carbonic acid, when the salt is saturated with an acid. An ammoniacal salt will also be found in the solution.

The explanation here given of the mode by which the cyanide of potassium becomes formed, is not quite satisfactory ; because the carbonate of protoxide of iron is decomposed before the reduction of the iron, and the separation of carbonic acid into carbonic oxide and ferroso-ferric oxide takes place, and it is at the expense of these that an intermediate quantity (certainly not greater than indicated by the formula) of cyanate of potash is formed.

The sides of the crucible, and also the remaining metallic iron, are left covered with cyanide of potassium, which is recoverable by dissolution in hot water. Heat this solution, and dissolve in it a small quantity of sulphuret of iron ; evaporate, and ferrocyanide of potassium is obtained. The mother-water will retain sulphuret of potassium.

NOTICES OF NEW PUBLICATIONS. The Dictionary of the Arts, Sciences, and Manufactures : Nlustrated

with Eleven Hundred Engravings; by C. FRANCIS, Esq., F.L.S.; Author of the Analysis of British Ferns; The Little English Flora ; The Grammar of Botany, fc. W. Brittain, Paternoster Row.

(Second Notice.) We expressed our high satisfaction of this work in a late number, and subsequent careful examination fully confirms our good opinion. We find upon calculation that more than 6,000 scientific and technical words have been collected, and of these a vast number are not to be found elsewhere. The labour of collecting them must have been immense. This alone renders the work truly valuable, nay indispensable, yet we think that a second design of the author, and one which he has admirably worked out, is even more valuable : he has given an accurate description of all useful apparatus and machines. There are more than 150 machines, &c., described on electricity alone, 13 thermometers, 21 different steam engines, and 14 presses; architecture, civil engineering, mathematics, mechanics, optics, and other departments of scientific knowledge are also liberally illustrated, the whole work containing, as we said on a previous occasion, no less than 1,100 engravings. Perhaps our readers may wish to judge for themselves of the character of the work from a portion of its pages, rather than trust to our opinion, we therefore give the following extracts, chosen not because of any particular attention which Mr. Francis paid to the science of electricity, but because they are accordant with the ordinary subjects of which we are accustomed to treat; and although we have confined our attention to the words relating to electricity, yet by the references in italics the far greater extent of the subject will be implied.

“ ELECTREPETER. An instrument for readily changing the direction of electrical currents. (See Clarke, Bird, foc.)

“ELECTRIC. All bodies are so called when they show electrical appearances upon being rubbed; or which will not permit the electric fluid to pass along them.

“ELECTRICAL, or ELECTRIC. Belonging to electricity. “ELECTRICAL AMALGAM. (See Amalgam.)

“ELECTRICAL APPARATUS, consists of all the machinery used to illustrate the science of electricity ; (for a particular description of each instrument see its substantive name, as Dance, Condenser, Discharger, Leyden Jar, Magic Picture, Thunder House, fc.)

“ELECTRIC ATTRACTION and REPULSION. One of the visible effects of a disturbance of the electrical fluid, when two bodies are excited or electrified in a similar manner, they repel each other; if excited so that one shall be in a different electrical state to the other, they will be attracted. Suspend two feathers on dry silken threads, and hold to them an excite glass tube, they will be attracted to it at first, being in a different state ; but afterwards they will be repelled from it, and from each other, because they are then, through imbibing the fluid from the glass, both electrified similarly.

“ ELECTRICAL CEMENT, for joining together the various parts of an electrical apparatus. Melt together five ounces of resin, one of bees’-wax, and one of red ochre. This may be employed in cementing the plates of metal in the galvanic troughs.

“ELECTRICAL CHARGE. The greatest quantity of the electric fluid which any body can be made to contain ; or the greatest degree of disturbance which can be given to its inherent fluid. The restoration of that fluid to a state of quiescence, is called the discharge or shock.

“ELECTRICAL CIRcuit. Any series of wires, or other conductors, intervening between the inside and outside of a charged Leyden phial, whereby the jar is discharged. Every thing which is to receive a shock must form a part of this circuit ; and connecting the outside and inside of such a jar or battery, is called completing the circuit.

“ ELECTRICAL CONFIGURATIONs. The peculiar radiating forms taken by certain powders when sifted upon charged electrics. They may be made as follows :-Put a sheet of dry glass on a piece of tin-foil spread on a table, and draw over the surface of it, in any fanciful device, the knob of a small charged Leyden jar; then, having ready tied up in a piece of loose muslin a mixture of equal parts of sulphur and red lead, in powder, sift them on the plate of glass, when it will be seen that the mixed powder will separate ; and while the sulphur of it settles in a close line on the exact tract of the knob, the red lead will arrange itself at a little distance on each side, in the most beautiful star-like ramifications. The following gives but a faint idea of the effect:

[graphic]

“ELECTRICAL Conductors. (See Conductors, and Lightning.)

“ELECTRICAL CURRENTS. The passage of the fluids from one place or object to another, through conducting substances : as for example, from the different sides of a charged jar; from one end of a galvanic battery to the other; along conducting wires, &c.; or when a current passes through a wire, which has another wire so near to it as to be affected by the passage of the fluid, the fluid which actually passes along the wire is called the primary current ; and that effect or disturbance which takes place in the approximate wire is called the secondary current.

“ ELECTRICAL Excitation. The power of disturbing the electric fluids, so that it becomes apparent either to our senses, or by the well known effects which it produces. Bodies thus influenced are said to be excited.

ELECTRICAL Fluid. That particular and universal power, substance, or property, which pervades all nature, occasioning, when disturbed, those appearances and effects, known in science as electrical and galvanic ; besides numerous natural phenomena, such as lightning, the aurora borealis, and perhaps the whole of the chemi

« ZurückWeiter »