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ON THE AGING OF FERROUS HYDROXIDE ANDFERROUS CARBONATE.BY OSKAR BAUDISCH AND L. A. WELO.

(From the Laboratories of The Rockefeller Institute for Medical Research.)(Received for publication, May 21, 1925.)

Interest in the aging of metal hydroxide has increased greatlyduring the past few years and it is due, no doubt, mainly to thefact that certain metal hydroxides have become useful for the isola-tion of enzymes and vitamins. The selective adsorption proper-ties of these hydroxides, aluminum hydroxide for example, makethem suitable for these purposes. Their surface forces make itpossible to separate unstable organic groups or compounds whichotherwise would not be obtained at all, or only with extremedifficulty. But the theoretical interest in the aging phenomenonhas also become more intense, since it is possible by modernmethods, especially by that of X-ray spectroscopy, to follow thechanges taking place in the hydroxides with time, and thus tocome to certain conclusions as to the nature of the adsorptionprocess. In this connection we have in mind particularly therecent work of Fricke and Wever (1) on aluminum hydroxide.Our own work is concerned entirely with ferrous hydroxideand ferrous carbonate. These substances are widely distributedin nature, and almost certainly play a very large part in manybiological processes. Our experiments were not originally plannedwith the purpose of getting data on the aging problem. Butthey led us to believe and finally convinced us that ferrous hy-droxide and ferrous carbonate, at the instant of precipitation,possess roperties which disappear very rapidly with time.

Since it was known that ferrous hydroxide and ferrous carbonateare exceedingly autoxidizable and, as a result of the absorptionof oxygen, form a series of compounds it was necessary to adopttwo distinct types of experiments in our study. The experi-ments had to be performed in: (1) the entire absence of oxygen ;i53

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754 Ferrous Hydroxide and Ferrous Carbonateand (2) the presence of air or oxygen. Much experimentalmaterial exists concerning the behavior of ferrous hydroxideand ferrous carbonate when oxygen has access to them, but asfar as we are aware, very li tt le is known about them when theyare precipitated under conditions which exclude oxygen.

We shall first discuss, briefly, the work that Just and Giinzburg(2) have done in this field. They made an exact study of thesolubilities of metallic iron and ferrous carbonate. They found,among other things, that the solubility of fresh ferrous carbonateis higher than that which has been aged, and that fresh ferrous car-bonate has the property of inereasing the supersaturation offerrous carbonate, whereas aged ferrous carbonate cannot do so.They concluded from this fact that the ions of the ferrous bi-carbonate must be different in their make-up than those of theaged ferrous carbonate. A further explanation of the wholequestion seems to demand additional experimental investigationof ferrous carbonate in its solid form.

In contrast to our very sparse information as to the chemicaland physical behavior of ferrous hydroxide and ferrous carbonatein the absence of air or oxygen, we have numerous publicationson the action of ferrous salts when they are in contact withoxygen. We have published some of the results obtained insuch work (3), and will here limit ourselves to a brief review ofthe action of oxygen on ferrous hydroxide and ferrous carbonatein as far as it concerns the formation of magnetic oxides.If ferrous hydroxide is oxidized under limited access of air,it can be shown in various ways that the oxidation goes mainlyto the stage Fes04*xH,0. In only a few cases does the oxidationproceed completely according to the scheme

Fe + 8 = FeIn by far the most cases the oxidation goes through numerousintermediate stages and we are very far from a thorough under-standing of the mechanism of the oxidation. Nature itselfdemonstrates to us through the large number of magnetic and non-magnetic ferro-ferric and ferric oxides, with their great varietyof color shades, that these oxidation processes must be exceedinglycomplex. Then, if the processes are further complicated by the


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0. Baudisch and L. A. Welo 755presence of other metals than iron and by the addition of organiccompounds, the possible compounds and processes become verynumerous indeed.As a working scheme we have adopted a formulation accord-ing to the theory of Werner which wiIl be briefly described asfollows :When oxygen has access to ferrous hydroxide, the followingprocess very probably takes place.

[ 1eOIL) 6 (OWr02+[ 1e (?H,i. (OH)z + 2Fe(zE = Fe(z>e) (OH)%[ 1HI. II.

From this graphical representation it is seen that at first anoxygen molecule reacts with ferrous hydroxide and that theresulting peroxo compound (I) can combine with the surround-ing, but as yet unchanged, ferrous hydroxide molecules, andt.hus forms what may be called a polynuclear complex salt (II).This complex salt has, however, a very short life, and throughthe splitting off of the coordinatively bound oxygen there isdeveloped a very labile, ferro-ferric compound in which the pro-portion of ferrous to ferric iron is 2 to 1. Hauser (4) has syn-thesized this weakly paramagnetic oxide Fez03.4Fe0.xHz0from ferro-ferric ammonium carbonate, and has found that,on further oxidation with molecular oxygen, it is converted intothe magnetite Fe0 *Fez03. Actually the proportion of ferrousto ferric iron is less than this formula indicates. If one passesoxygen over this magnetite at a temperature of 200C. it is stillfurther oxidized, as we have found into the ferric oxide, Fe203,and becomes even more ferromagnetic. The reason why weare concerned with the magnetic properties of the oxides of ironis made clear in our previous paper (3). From the experimentsdescribed here it becameparticularly clear that the properties of theoxides were really determined by conditions existing at the momentof precipitation of the hydroxide from which they were derived.We could also conclude that the reduction of potassium nitrate


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756 Ferrous Hydroxide and Ferrous Carbonatewith oxygen and ferrous hydroxide is a molecular reaction. Asfar as the present paper is concerned the important result wasthat the reduction of nitrate to nitrite was extremely rapid, andthat on the aging of the precipitated hydroxide of only a few secondsthe reduction of the nitrate was decreasedmore than half.The foregoing observations relate to the things observed whenworking in the presence of air or oxygen. But we have alsoobserved that ferrous hydroxide is subject to an aging processin the absence of oxygen, and the phenomena are in completeaccordance with the observations and conclusions of Just andGiinzburg, which have already been discussed.To secure absence of oxygen from our solutions of ferrous sul-fate and sodium hydroxide, from which the ferrous hydroxidewas precipitated, it was necessary to boil each solution separatelyand to cover them with atmospheres of pure hydrogen previousto the mixing. This was convenient.ly done with the apparatusshown in Fig. 1.We usually had the lower bulb half full of sodium hydroxidesolution and the upper bulb half full of a solution of ferroussulfate. On boiling, the air and steam escape hrough the barom-eter tubes dipping into wells of mercury. This arrangementof barometer tubes also acts as a safety valve against too highpressures while boiling. As the bulbs cool off, the pressuresdecrease and hydrogen is drawn in until the solutions havecooled off to room temperature. When cool, the ferrous sulfatein the upper bulb is run into the lower one, and becomes mixedwith the solution of sodium hydroxide. A snow-white ferroushydroxide is formed which remains white, even on standingseveral days, and apparently does not change in any way. Nordoes t decomposewater or change n any way in general appearance,even if the mixture containing the precipitate is boiled for severalhours. However, if only a trace of air is admitted, the whiteflocculent precipitate changes to a green color which, in turn,becomes black if air is admitted in larger quantities.If we repeat the experiment, but with the difference that thesolution in the lower bulb contains potassium nitrate, in additionto sodium hydroxide, the results are exactly the same. A whiteflocculent precipitate is formed which, even on boiling for a longtime, remains the same in color. It does not matter how much


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0. Baudisch and L. A. Welo 757or how little nitrate is present. If oxygen is kept away, thereis no change in the nitrate at room temperature, nor at the boilingtemperature. The fact that the ferrous hydroxide remainswhite and does not change from white to green or black is con-

Edte m centlmetws0 2 4 6 8 10

FIG. 1.

vincing evidence that the potassium nitrate has not been changed.But, in order to make doubly sure, direct tests for the presence ofnitrite or ammonia in the solution, which had contained theprecipitate for several days, were made. There were no nitritesor ammonia, and hence no reduction product.


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158 Ferrous Hydroxide and Ferrous CarbonateThe results are entirely different if, instead of potassium nitrate,potassium nitr ite is used. Even in the complete absence of

oxygen, the nitr ite reacts with ferrous hydroxide and forms adeep green complex compound which, on decomposition, yieldsammonia as a reduction product.

Before passing to a detailed consideration of the aging process,it is well to describe some quantitative experiments on the reduc-tion of nitrates with oxygen and ferrous hydroxide. The usualprocedure was as follows, using the apparatus shown in Fig. 2.

FIG. 2.

In the flask were put 400 cc. of distilled water, in which hadbeen dissolved known quantities of sodium hydroxide and of thepotassium nitrate to be reduced. Then 100 cc. of a solution offerrous sulfate were added. The solutions were thoroughlymixed by shaking. The mixture was then distilled until the

1 With the simple apparatus shown in Fig. 2, we can also show that potas-sium nitrate is not reduced in the absence of oxygen. The oxygen beingfirst excluded by boiling the mixture of ferrous sulfate and sodium hydrox-ide, the potassium nitrate is added afterwards by means of the smalltest-tube suspended from the stopper and indicated in the drawing assubstance.


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0. Baudisch and L. A. Welo 759TABLE 1:

Red uction of Alk ali Nitrate by Ferrous Hydra&e.Amounts used: 0.1702 gm. of NaNOs in 500 cc. of water. Complete re-

duction would give 0.0340 gm. of NHa. TFeSOa

-

.-*m .4.84.84.84.84.84.84.84.84.84.84.84.84.8 -

NH3 formed.Equivalent. -

?

-

,

-

NaOH FreeNaOH. Amount.

-.per cent vn.

0 (neutral). 0.03400.12 0.022440.26 0.013090.52 0.009520.78 0.005441.04 0.004761.30 0.004253.08 0.003443.10 0.003234.14 0.003064.88 0.002896.50 0.001876.68 0.00153

! m L2.63.23.95.26.57.89.1

18.020.023.227.035.136.0

MT cen

1006638.528161412.5109.5

98.55.54.5

123456789

10111213

2222222222222

0 (neutral).0.512345

11.81215.818.72525.7

*From Baud&h, O., and Mayer, P., Biochem. Z., 1920, cvii, 1.TABLE 11:

Reduction of Alkali Nitrate by Ferrous Hydroxide in the Presence and Abse nceof Oxygen.0.1702 gm. of NaNOa 14 .8 gm. of FeSO+ 500 cc. of HzO.-

- 4mount of nitrate reduced.quivalent.NaOHFlV.3. NaOH With Withoutoxygen. oxygen.

w% per cent per cent per cent2.6 0 (neutral). 0 100 04.0 1 0.28 38.5 09.1 5 1.38 12.5 020.0 12 3.1 9.5 0

14151617 -

*From Baudisch, O., and Mayer, P., Biochem. Z., 1920, cvi i, 1.Nessler reagent no longer showed a yellow color, the distillationbeing usually complete when 150 cc. of liquid had been boiIed off.The results are exhibited in Tables I and II and in Fig. 3.


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760 Ferrous Hydroxide and Ferrous CarbonateFrom the tables and the figure it is seen that, when the nitrate

is reduced by ferrous hydroxide, in the presence of air, throughpotassium nitrite, to ammonia, the behavior is quantitativelyregular. With increased concentration of free alkali in thesolution, that is, with increasing amount of alkali not used bythe ferrous sulfate, the yield of ammonia and hence the amountof nitrate which is reduced falls off in a manner entirely quantita-tive. If the same experiment is carried out in such a way as toexclude air or oxygen, the nitrate remains absolutely unchanged.We regard the action of the alkali as being that of an Anlage-rung of NaOH to the molecules of ferrous hydroxide, similar

to that which Miolatti and Bellucci (5) have shown to take placebetween potassium hydroxide and platinum hydroxide. Theirresults may be expressed by the reaction

Pt (OH)4 + 2KOH + (OH)., Pt g; --+ [Ft (OH)s]K t

What may here be considered as the blocking action of thealkali is in complete harmony with our previous explanation of themechanism of nitrate reduction. We are dealing with a competi-tion between the oxygen and the alkali molecules for the un-saturated ferrous hydroxide molecules. If the solution is neutralal l of the ferrous hydroxide molecules can combine with theoxygen dissolved in water and form the peroxide


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0. Baudisch and L. A. Welo 761Each peroxide molecule reacts with a nitrate molecule and onthe splitting off of an oxygen atom from the latter a nitrite isformed. On the other hand, if free alkali is present in the solu-tion, ferrous hydroxide presumably combines with this accordingto the reaction

Fe (OH)2 + NaOH -+ [Fe (OH),] Naand the ferrous hydroxide is no longer available for the reductionof nitrate.It was found that the oxygen which becomes coordinativelybound to the ferrous hydroxide can be used not only for thereduction of nitrate, but it is also capable of oxidizing certaininorganic and organic compounds. A complete discussionwill be made the subject of another paper. We shall only pointout here that our view of the special properties of ferrous hydrox-ide-peroxide is completely valid in this case. As more andmore molecuIes of the substance to be oxidized, lactic acid, forexample, combine with the nascent ferrous hydroxide-peroxidemolecules, there is a corresponding increase in the yield of pyruvicacid.From all of the foregoing it can be seen that the study of thereduction of nitrate has enabled us to gain a considerable insightinto the mechanism of this peculiar action of ferrous hydroxideand oxygen. But the study has, in addition, provided us witha foothold from which the investigation of the aging of the ferroushydroxide or carbonate may be carried out in the absence ofoxygen.If ferrous hydroxide is precipitated in the absence of oxygen,the white voluminous precipitate formed in the lower bulb ofFig. 1 settles gradually to the bottom with no apparent change inits properties. If the experiment is again carried out with thedifference that potassium nitrate is also present during the pre-cipitation, no visible change in the precipitate with time is ob-served. There is, then, no obvious reason for believing that anychange has taken place in the hydroxide, even after it has becomeseveral hours, or even days, old. If air is admitted through theslender tube extending down into the lower bulb, and allowedto bubble through the mixture, the ferrous hydroxide changesthrough several intermediate stages nto the red ferric hydroxide,


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762 Ferrous Hydroxide and Ferrous CarbonateFe(OH)s, so that there seems to be no difference between freshand aged ferrous hydroxide, as far as the property ofabsorbing oxygen is concerned. This may, indeed, be thereason that the rapid aging of ferrous hydroxide has heretoforeescaped detection. However, although the aged hydroxide orferrous carbonate retains its marked property of being autoxi-dizable, it has lost completely the property of being able to reducenitrate or to oxidize organic compounds such as ziracil and lacticacid.Several experiments have been made to illustrate this.

Experiment I.-I f ferrous carbonate (10 gm. of Na&03 and 3 gm. ofFeS04) is precipitated in the presence of 0.1 gm. of sodium nitrate in a sealedtube, preventing entrance of air, and keeping at room temperature, there isformed a snow-white product which does not change in appearance afterstanding for over 6 hours. I f the tube is then opened to the air, and isshaken, the white ferrous carbonate takes on a deep blue-green color in aminute or two, as a result of autoxidation. In spite of continued shaking,and addition of oxygen, the nitrate is not reduced and not a trace of nitriteor ammonia is found in the filtrate.Ferrous hydroxide was tested in a similar manner, with similar results,only that the nitra;te was added to the mixture after the ferrous hydroxidehad been aged.

Experiment 2.--1.3 gm. of sodium hydroxide were dissolved in 500 cc.of water, and the solution was boiled to drive off oxygen. Taking care thatno air entered, a solution containing 4.4 gm. of ferrous sulfate was addedand the precipitate was left in the sealed flask to age for 8 hours. Then theflask was opened, nitrate added, and the mixture shaken with air. Thewhite precipitate was still autoxidizable, turning first dark green, andfinally red as the iron became oxidized. The nitrate, however, remainedunchanged, the tests for nitrite and ammonia being all negative.

These experiments prove that ferrous carbonate and ferroushydroxide, when aged out of contact with oxygen, lose the propertyof reducing nitrates to nitrites, althouth they retain their ability toabsorb oxygen from the air and can be oxidized to ferric compounds.This fact becomes even more striking if an attempt is made to

use the ferrous hydroxide or ferrous carbonate, which has beenaged for a few hours, for the purpose of oxidizing certain organiccompounds, let us say, uracil or lactic acid. These organic com-pounds can, as has been mentioned, easily be oxidized by freshlyprecipitated ferrous hydroxide or ferrous carbonate if air hasaccess. On the other hand, if the ferrous hydroxide or ferrous


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0. Baudisch and L. A. Welo 763carbonate be left to age for a few hours, they remain autoxidiza-ble, but the molecular oxygen then absorbed can no longer oxi-dize the uracil or the lactic acid which may be present.

The following experiments sustain this conclusion.Experiment 5.-0.015 gm. of uracil and 5 gm. of sodium bicarbonate are

dissolved in 400 cc. of water. Th is may be calle d Solution A. To this isadded a solution containing 5 gm. of ferrous sulfate and the mixture isshaken with air until all of the iron is oxidized to Fe (OH)a. The filteredsolution shows every reaction charac teristic of oxidized uracil.

Experiment &-Experiment 3 is repeated with the difference that Solu-tion A is first boiled to drive off oxygen. Ferrous carbonate is added to thec6oled Solution A, care being taken to keep air away, and the mixture isallowed to stand for 4 hours. Then the flask is opened and shaken with airuntil the iron is oxidized to Fe (OH)a. The filtrate obtained in this experi-ment showed no oxidized uracil. It contained only unchanged uracil.Although the precipitation of ferrous bicarbonate took place in the presenceof uracil, there was no oxidation on the subseque nt adm ission of oxygen.The ferrous bicarbonate had been aged, and was ineffective as an aid to theoxidation.

Similar results were obtained on the oxidation of lactic acidto pyruvie acid. Here, t,oo, it is true that it is only the freshlyprecipitated ferrous bicarbonate which is able to bring aboutoxidation when oxygen is admitted. After the bicarbonate hasaged for a few hours, it is still, indeed, autoxidizable, but it is notable to aid the oxidation of lactic acid.

From the experimental results we have here described, andfrom our previous work, there appears a whole series of factswhich will now be briefly analyzed.Freshly precipitated ferrous hydroxide alone does not reactwith potassium nitrate nor with the alkali salts of, say, lacticacid or succinic acid, nor does molecular oxygen alone react withthese same compounds. However, if one gives both of the sub-stances, ferrous hydroxide and molecular oxygen, the opportunityto react with each other, there is formed a chemical compoundhaving an extraordinarily great react.ive tendency which canchange the potassium nitrate, if simultaneously present, to potas-sium nitrite. This strongly reactive ferrous hydroxide-peroxidecan also oxidize lactic acid into pyruvic acid. Both of thesereactions, the oxidat,ion, as well as the reduction, are a directfunction of the oxygen dissolved in the wat,er which contains the


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764 Ferrous Hydroxide and Ferrous Carbonatereacting substances. This molecular oxygen in solution isactivated as a moEecule. If it is still a molecule when it performsthe oxidation, or if it is first split up into the atoms, we are notable to decide with our present experimental material. Butthe fact remains that under the given conditions, namely attach-ment to the iron atom, the oxygen has gained a markedly greatchemical activity. This activity is so great that even in thestrongly reducing medium formed by an excess of unchangedferrous hydroxide molecules it is able to oxidize such substancesas lactic acid or succinic acid, which are ordinarily so difficultto oxidize. .

This great oxidizing ability belongs, however, only to theoxygen which has been activated by the freshly precipitated ferroushydroxide or ferrous bicarbonate. If the freshly precipitatedferrous hydroxide or ferrous bicarbonate is rapidly centrifugedout. and then used for autoxidation in the presence of the sub-stances mentioned, there is not the slightest trace of any chemicalchange in them. The coordinatively linked oxygen attached tothe iron atom of the ferrous hydroxide which has been aged forso short a time possesses no longer such a high oxidation potential.It is only able to oxidize those substances having very labi lehydrogens, such as they are in para-phenylenediamine, or inbenzidine. This oxygen can also no longer reduce potassiumnitrate.

These results of our investigations furnish a striking proof ofthe fact that compounds or atoms in their nascent states havevery different properties than they have after they have beenaged. With an appreciation of this fact, many of the mysteriesconnected with some of the intensive chemical reactions occurringin living cells at the ordinary body temperatures disappear en-tirely. We shall not discuss here the mechanisms of the oxida-tion and reduction, as they occur in the natural processes, withany great detail. It is most probable that, at the moment offormation, the ferrous hydroxide-peroxide acts so as to dissociatewater, and forms a strongly activated oxygen and atomic hydro-gen. This process of activation may be represented by


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0. Baudisch and L. A. Welo 765If we assume this we have a natural explanation of the doublerole played by the freshly precipitated ferrous hydroxide-perox-ide in its strong oxidizing action and its strong reducing action.

An analogous chemical action takes place when molecularoxygen comes in contact with the aged ferrous hydroxide orferrous bicarbonate. But there is a difference in the degree ofthe activation. In this case the activated oxygen which isformed does not have such a high oxidation potential and canonly oxidize those compounds having hydrogen which is labileand which is easily removed.Similar relations can be followed for the stages of activation ofhydrogen. There are many examples to show that when onedissociates water one obtains hydrogen of a very wide range ofreducing power, according to the chemical or physical conditionof the metal used for the dissociation. The chemical activityof hydrogen obtained by the dissociation of water varies enor-mously and the process is very complicated.If aged ferrous hydroxide or the magnetite obtained therefromis autoxidized in the presence of lactic acid or of potassium nitrate,both of these substances remain unchanged, although molecularoxygen is activated in some degree. There exist, between thefresh and the aged ferrous hydroxide, differences which are anal-ogous to the differences found between the active and theinactive forms of ferric oxide, Fe,Oa. We have found thatactive ferric oxide decomposes hydrogen peroxide, yielding anactive oxygen which oxidizes benzidine. The inactive ferricoxide, on the other hand, on decomposing hydrogen peroxide,yields only the molecular oxygen which does not oxidize thebenzidine. Ferrous hydroxide freshly precipitated in the pres-ence of oxygen can oxidize lactic acid by the removal of it.shydrogen. Aged ferrous hydroxide, on the other hand, can re-move only labile hydrogen atoms, such as are found in paraphenylenediamine, for example.It is our intention to study certain of the physical propertiesof those iron compounds which activate oxygen, and to attemptto correlate the activation to their molecular and atomic struc-ture. At the present time we really know very Mtle about theadsorption and the activation of gases. This statement is partic-ularly true of those with which we are concerned here, oxygen


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766 Ferrous Hydroxide and Ferrous Carbonateand hydrogen. It is to be expected that with more detailedinformation as to the structure of these iron compounds we cancome to an understanding as to their adsorbing action towardsvarious gases. The activation of the gases is, however, most,probably a complex change t,aking place in the atoms themselvesand just beyond the reach of the present experimental methods.Just now the prospects are very poor for getting the informationwhich will enable us to understand the several degrees of activa-tion and the selective behavior of the activated oxygen orhydrogen towards other compounds. From our experimentsand investigations we believe we can safely say that there areseveral different lcinds of activated oxygen, and that the hithertorecognized active forms of oxygen, such as atomic oxygen orozone, represent only the more stable forms.

Now, as to the nature of the changes taking place in the ferroushydroxide or ferrous bicarbonate, or the ferrous hydroxide-peroxide, during the time of aging we have little or no informationwhich has been obtained from these substances themselves.But they may be expected to be of the same nature as thosewhich have been found to take place in aluminum hydroxide;namely, a gradual passing, during the aging, from an apparentlyamorphous to a very definite crystalline form, During theaging process there occurs an ordered arrangement of the forcesamong the iron atoms and the hydroxyl groups, and small crystalsare formed which retain some of the properties that the sub-stances had in the amorphous state, but have lost others. Theferro-ferric oxide, Fe,O,, which has so often been mentioned, isa known and striking example of such a case. If the attemptis made to use the newly prepared oxide, Fe304, for the purposeof reducing potassium nitrate, the result is always absolutelynegative. But it can absorb more oxygen, although it already hasa perfectly definite crystal structure (6), such as is shown inFig. 4; and the structure is not disarranged during this increaseof the crystals oxygen content. On examination of the inter-atomic dimensions involved, it was found that room can actuallybe found in the structure, shown in Fig. 4, for sufficient oxygento convert the magnetite, FeaOr, into the ferric oxide Fe&,without changing the arrangement of the iron and oxygen abomsalready in place.


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0. Baudisch and L. A. Welo 767It is noticed that the unit cube (Fig. 4) contains 8 molecules,

so that FeaOa may be written Fez40s2. After oxidation to Fez03the corresponding composition would be FezeOos. We mustfind room for 4 additional oxygen atoms in the cube. The firstplaces to suggest themselves are the centers of the tetrahedraformed by the trivalent iron atoms, and they are thus shown inFig. 5. In view of the uncertainties as to the actual radii ofcombination, it is quite possible that the extra oxygen atoms arepIaced, as shown, without undue distortion of the system. The

MAGNETITEAGNETITEFra. 4.ra. 4.

edge of the unit cube has a length a = 8.30 ii. u. and the distancefrom the center of the tetrahedron formed by trivalent iron atomsto each corner is

g- t/3 = 1.795 Au.

The radius of the oxygen atom is usually taken to be 0.65 A. u.This leaves 1.145 8. u. as a remainder for the radius of the ironatom. The radius of, the iron atom appears to be variable andvalues as low as 1.25 A. u. have been found in the case of pyrites(7) and in iron itself.


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768 Ferrous Hydroxide and Ferrous CarbonateAn alternative and equivalent arrangement would be to place

an oxygen atom at the middle of each edge of the cube and onein the center. The room at our disposal would be the same.The question is not considered here. We are here concernedonly with the possibility of putting more oxygen in Fe304 so as toconvert it to FezOB without changing the existing arrangementof the atoms. And we are especially concerned with the factthat we are dealing with a known substance which has the prop

0 &; l Oj 0 EXtMO.

OXIDIZED MAGNETITEFIG. 5.erty we have assumed for the precipit,ated ferrous hydroxideand ferrous carbonate. It is that, while becoming crystalline, itloses certain specific properties, such as its reducing and oxidizingpowers, and yet remains capable of absorbing still more oxygen.

It must be explained here that the structure of Fez03 in Pig.5 is not the most stable form. FezOs of that structure is obtainedby oxidizing Fe304 in oxygen at a temperature of about 200C.On reaching a temperature of 550C. or more the structurebecomes unstable and goes over into the more stable calcite-like structure usually found for FezOs as shown in Fig. 6. Themost recent determination of this stable structure is that ofPauling and Hendricks (8).


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0. Baudiseh and L. A. Welo 769It is our intention to proceed further with this work on the

aging of ferrous hydroxide and ferrous carbonate. In particular

HematiteFIG. 6.

it is our plan to follow by X-ray analysis the conversion of thehydroxide or the carbonate from the apparently amorphous tothe crystalline condition.

BIBLIOGRAPHY.1. Fricke, R., and Wever, F., 2. anorg. C/mm ., 1924, cxxxvi, 321.2. Jus t, G., and Giinzburg, J., Jakoh Giinzburg, Inaugural disser tation,

Karlsruhe, 1911.


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770 Ferrous Hydroxide and Ferrous Carbonate3. Baudisch, O., and Welo, L. A., J. Bid. Chem., 1924, lxi, 261.4. Hauser, Ber. them. Ges., 1905, xxxviii, 2707.5. Miolatti and Bellucci, Atti accad. Lincei, 1908, ii, 635.6. Wyckoff, J. Franklin Inst., 1923, 531,544.xcv,7. Bragg, W. H., and Bragg, W. L., X-rays and crystal structure, New

York, 4th edition, 1924, 172.8. Pauling, L., andHendricks, S. B., J. Am. Chem. Sm., 1925, xlvii, 781.


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