POINTS CONNECTED WITH SMALL POX AND VACCINATION..

358 for instance, as cyanide of potassium absorbs oxygen with a volatile oil, such as oil of roses, for instance, with ether,-the volatile oil separates from the water, being withdrawn avidity at a red heat, and becomes thus converted into cyanate from this menstruum by thO!. ether. But this separation of the of potass, it is necessary to exclude the access of air very carevolatile oil from its aqueous menstruum is owing to the solubility I, fully upon exposing to a red heat animal matter, together with of the oil in ether. Now the separation of the ferrocyanic acid carbonate of potass; fusion in well-closed iron pans must there’ from its aqueous menstruum takes place without subsequent solu- fore be preferred to fusion in stoves, at a blazing fire. Further: were sulphate of potass excluded entirely from the tion of the acid in the ether. It seems, therefore, in this instance, as if the separation of the ferrocyanic acid from its aqueous menmass, this would completely prevent the formation of sulphuret struum were dependent upon the insolubility of this acid in water of potassium, and consequently that of sulphuret of iron, and saturated with ether; it is, however, possible, also, that the ether thus the iron pans used for the fusion of the animal charcoal with forms with the ferrocyanic acid a compound insoluble in water carbonate of potass would not suffer any deterioration. To and ether, and which compound yields up its ether upon being transform the cyanide of potassium, which the crude fused mass dried in the air. contains, into ferrocyanide of potassium, it is sufficient to treat this Dried ferrocyanic acid is anhydrous; it remains unaltered in a mass with cold water, so as to dissolve its soluble part, to mix the dry atmosphere, but in moist air it becomes converted, with loss solution obtained with iron turnings or iron filings, and to expose of hydrocyanic acid, into a blue powder, very much like prussian the mixture, in flat iron vessels, for some time to the action of blue. Ferrocyanic acid, when heated in carbonic acid gas to the the atmosphere. Under these circumstances the iron becomes boiling point of water, decomposes into hydrocyanic acid and dissolved in a very short time, and ferrocyanide of potassium is white protocyanide of iron. I have already stated that ferro- formed, corresponding in amount to the quantity of cyanide of

solution of

cyanic acid dissolves in alcohol. This alcoholic solution is of the consistence of a syrup, and when brought under the exhausted receiver of an air-pump, it solidifies into a solid, hard crystalline

potassium present.

mass.

potass.

This

ferrocyanide

of

potassium crystallizes

out of the

solution, upon the concentration of the latter; the

remaining

decanted mother

liquor is evaporated,

and used

as

It has been asserted by several chemists, that the transmission of Ferrocyanide of potassium is manufactured, on a large scale, by exposing dry carbonate of potass, together with calcined blood, atmospheric air through a mixture of charcoal and carbonate of horn, hoofs, and bristles, in iron vessels, to a red heat, until the potass, at a white heat, gives rise to the formation of cyanide of whole mass is in a state of fusion, and evolves no longer any gas ; potassium, and, in explanation of this asserted fact, these chemists the mass is then removed from the vessels and washed, after have given it as their opinion, that at this high temperature the cooling, so as to dissolve its soluble part; the solution is then nitrogen of the atmosphere combines with the carbon, forming evaporated. The ferrocyanide of potassium which crystallizes cyanogen. This assertion, and the inference drawn from it, from it, upon this evaporation, is not quite pure; it is therefore have, however, been contradicted and disproved by the experipurified by re-crystallization. The method adopted at several ments of other chemists, who state that they did not observe the manufactories is to fuse the mixture of carbonate of potass with formation of cyanide of potassium under these circumstances. animal charcoal, with a bright fire in stoves, similar to soda Yet upon this but slenderly supported assertion, a method has been devised of producing large masses of cyanide of potassiumstoves. It is only recently that the theory of the formation of this salt for the fabrication of ferrocyanide of potassium; manufactories has been more closely studied, and its true nature apprehended. have been established for this purpose at Paris and at NewFrom the manner of preparation of cyanide of potassium, which I castle, where the production of cyanide of potassium by this have described to you on a former occasion, it is self-evident that method has been attempted, but the results obtained havea mixture of ferrocyanide of potassium with carbonate of potass, hitherto proved unfavourable. The experiments made in theseafter having been exposed to a red heat, can no longer contain manufactories will, however, at any rate, decide the question any trace of ferrocyanide of potassium, but simply cyanide of whether the nitrogen of the atmosphere is capable of entering,potassium; it has, indeed, been found that the crude mass, ob- into chemical combination in presence of potassium and charcoal tained upon fusing carbonate of potass together with animal —afact which has hitherto been, with reason, disputed. It is a remarkable circumstance, that the black mass which, in charcoal, contains no ready-formed ferrocyanide of potassium, but simply cyanide of potassium, and that the ferrocyanide of potas- the production of potassium from calcined tartar, passes over sium forms only upon the solution of the crude mass in water. together with the potassium, as I had occasion to remark, in the The formation of this salt, under these circumstances, rests course of a former lecture, leaves upon its rectification, for the upon the deportment of cyanide of potassium with sulphuret of purpose of obtaining the potassium which it contains, a residue iron and metallic iron. The carbonate of potass employed in the which yields a copious amount of prussian blue when brought into fabrication of ferrocyanide of potassium, is never free from sul- contact with hydrochloric acid and an iron salt. It is evident, phate of potass, which at a red heat becomes reduced by char- therefore, that this residue contains cyanide of potassium, thecoal to a mixture of bisulphuret of potassium with potass : this nitrogen of which cannot proceed from the atmosphere, but must bisulphuret of potassium yields part of its sulphur to the iron of exist in the carbonate of potass prepared from purified tartar. the iron vessel in which the fusion is effected, sulphuret of iron The further consideration of the properties and reaction of is formed, and this dissolves in the fusing mass. Upon the sub- ferrocyanide of potassium I will defer till the next lecture.

sequent solution of the fused mass in water, with the application

of a gentle heat, the sulphuret of iron dissolves in the cyanide of potassium and ferrocyanide of potassium and sulphuret of potassium are formed. It is owing to the formation of sulphuret

POINTS CONNECTED WITH SMALL POX AND VACCINATION..

The following replies -were made by Mr. MARSON, at a late of iron that the iron vessels become perforated and useless, after having been for some time employed in the preparation of ferro- meeting of the Westminster Medical Society, to questions cyanide ofpotassium. The tendency of cyanide of potassium put to him by various members:- The Small-pox Hospital of potassium when in was nearly full at the present time, seventy patients a to become converted into &rrocyanide month having of late been received. With two exceptionscontact with iron, is exceedingly great. Upon heating metallic iron with a concentrated solution of viz., 1781 and 1838-the hospital has never, since its founcyanide of potassium, taking care to preclude the access of air. dation, contained a greater number of patients. The character the iron dissolves, hydrogen gas being evolved at the same time. of the disease presented nothing unusual, and was fatal from Ferrocyanide of potassium and oxide of potassium are formed; the same causes as formerly. As a proof of the increase in upon moistening metallic iron with a solution of cyanide of vaccination, as many protected patients, as unprotected, had of late potassium, oxygen is absorbed with great rapidity, and this been received into the hospital-a circumstance quite new in the oxygen combines with part of the potassium. The oxide of history of the institution. Of the patients admitted after vaccipotassium which is thus formed,, separates, and the portion of nation, five out of six were between the ages of eighteen *and potassium which it withdraws from the cyanide is replaced by an twenty-three. In those whom the cicatrix ofcow-pock was perfect and well-marked, the small-pox was three times less fatal equivalent amount of iron. Ferrocyanide of potassium is decomposed at a red heat into than when the cicatrix was imperfect. The new vaccine lymph carburet of iron and cyanide of potassium. This decomposition, left a better cicatrix than the old matter. He had re-vaccinated. as well as the deportment which I have just now described, about three thousand persons ; the vesicle seldom went through proves evidently that the crude mass obtained by fusing carbo- its proper stages; the areola was irregular, and the progress of nate of potass at a red heat, together with animal charcoal, the vesicle subsided about the fifth day. Females about nineteen cannot contain any ferrocyanide of potassium, but must consist seemed to be most susceptible of the influence of re-vaccination. Dr. AYRES had found, in two cases, that the blood of smallsimply of cyanide of potassium. From a due consideration of these facts and circumstances may be derived a few useful hints pox patients was remarkably thin, the clot being so loose that he concerning the fabrication of ferrocyanide of potassium : thus, could draw his finger through it. ,

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