NEWS are present in solution and that as these are transported by the current others are liberated spontaneously and take their place. I have always maintained that this interpretation should not be put on the facts. The experiment quoted by Helmholtz in his Faraday lecture, on which reliance is placed, is not a valid proof, as the means used to remove oxygen from the liquid (viz., a third electrode of palladium charged with hydrogen) could not effect this object completely and some hydrogen would necessarily pass into solution, otherwise there would be no equilibrium; the inevitable consequence would be that the electrodes would remain more or less polarised. I even venture to think that the Helmholtz atomic charge hypothesis is entirely open to question. We have been taught to think of hypothetical simple ions-free ions-as carrying the charges; but in point of fact the bodies we charge are always highly complex viscous electrolytes of low conductivity; it may therefore be questioned whether there be any proof that individual ions can be charged, whether it be not more probable that the charge is always carried by a complex system. The conditions in a solution are certainly by no means simple; in fact, it is little short of impossible to avoid the conclusion that behind the apparent simplicity of Faraday's law there is probably a give-and-take process at work of which no account can be rendered, the summation result of which alone has been taken into account in framing the hypothesis. The atomic charge hypothesis, moreover, is not in accordance with our conceptions of valency. Thus in a series of oxides taken in the order of their heats of formation, commencing with those in the production of which but little heat is evolved, such as silver oxide, heat is developed if the metal in any one of the oxides be displaced by that of the oxide next below it in the series. If the two charges of the oxygen atom be given up in the formation of the initial term of the series, whence-it may be asked-is the energy derived which is liberated each time on passing to an oxide having a higher heat of formation? It cannot well be supposed that the oxygen remains a non-contributor and that the energy is derived from the metal alone; whatever the nature of the process, metal and oxygen are in some way reciprocal agents. In like manner, the properties of water are incompatible with the assumption that the two single charges of the two hydrogen atoms simply neutralise the two charges of the oxygen atom. Physicists have never attempted to deal with facts such as these. The conception of a definite "valency volume" recently introduced by Barlow and Pope may well prove to be applicable to the problem: it is conceivable that the volume of material displaced in electrolysis is in some way proportional to the power of the displacing agent. The majority if not all of the results arrived at by the application of the ionic dissociation hypothesis are independent ot the fundamental premises which underlie it and depend merely on the recognition of the fact that the order in which electrolytes exercise their chemical activity is practically the order of their activity as electrical conductors in an electrolytic circuit. Any hypothesis which would satisfy this relationship might take its place; indeed, for many purposes of calculation, it is probably unnecessary to go further than to assume that it is established and | to make no hypothesis in explanation of the fact; whilst in cases in which it is necessary to go further, it is probable that the phenomena are by no means so simple as is supposed and that conclusions based on the application of the hypothesis cannot be accepted even provisionally. The fact that discussion has been confined almost entirely to weak solutions has been a most fertile source of misconception: when all degrees of concentration are considered, results are arrived at which are by no means such as should follow from the premises adopted. Comparing, for example, electrical conductivity with hydrolytic activity although the order of activity of a series of hydrolysts is that of their activity as electrolytes, in the one case (hydrolysis), there is a decrease, in the other (electrolysis) an increase of "molecular " activity as the concentration is diminished; furthermore, when nitric is compared with chlorhydric acid, whereas the hydrolytic activity of the nitric is always inferior to that of chlorhydric acid at all concentrations and the more so the weaker the solutionin the case of conductivity, in moderately and very dilute solutions chlorhydric acid is a better conductor than nitric acid but in concentrated solutions it is a worse conductor, the difference becoming the more pronounced the stronger the solution. The values given in Table I. have been obtained by Mr. Wheeler and myself in a set of preliminary experiments. There is a well-known adage that you cannot have your cake and eat it if conductivity and hydrolytic activity were both properties to be referred to the operations of dissociated ions, they should run not only on more or less parallel lines but also in similar directions: in point of fact, they run in opposite directions; it is rational, therefore, to assume that the two processes are essentially different in character, not similar as the dissociationist school would have us believe. The Faraday theory of chemical change, as I propose to term it, involves the assumption that the conditions operative in a voltaic cell must be realised before any change can take place-that is to say, that a conducting system must be established consisting of at least three components; no less a number, I imagine, will afford a slope of potential. One of the components must be an electrolyte of the two remaining members of the system, the one must be a substance-a metal, for example-with which the negative radicle of the electrolyte can be associated; the other may be either active or neutral (in the chemical sense) towards the positive radicle of the electrolyte. The only difference between the case of a voltaic battery and that of a chemical change taking place in a fluid mixture without electrodes is that in the battery conducting electrodes or feelers are introduced which enable us to tap the circuit and utilise the energy set free in the interactions. In a fluid medium, this energy is frittered down into heat: in any case, our chance of being able to utilise the energy of chemical change as electricity depends on our ability to interrupt the circuit by the interposition of conducting terminals. The remarkable results arrived at by Dixon and by Brereton Baker with which, it may be supposed, all are familiar,* have always appeared to me to afford complete It is noteworthy that they are entirely disregarded by the ionic dissociationist school. Justification of the above conclusions. Baker's observations show that liquid water alone does not promote the interaction of hydrogen and oxygen gases; change only takes place when impurity is present-that is to say, when the water becomes a composite electrolyte. Larmor, in his recent Wilde Lecture, has dwelt on the probability of encounters taking place between pairs of the different molecules rather than between any greater number of molecules in a mixture of gases. I venture, however, to think that the experimental evidence is of so convincing a character that it may be affirmed that whatever the statistical probability of an effective meeting may be, the mating of the hydrogen and oxygen molecules is necessarily dependent on the advent of a suitable composite electrolyte so that the patience of the molecules within the mixture must be exercised until proper opportunities occur for the interchange of affections-i.e., for affinity to operate; probably no great demand is made, because of the almost infinite rapidity with which molecular motion is propagated in gases, especially under compression. From the point of view here advocated chemical interchanges are essentially all associative processes and their occurrence is dependent on the operation of a catalyst. But of late the doctrine has been promulgated that a catalyst is a substance which merely accelerates changenot one which directly conditions change; that the actions which take place more or less rapidly under the influence of catalysts also take place without them but so slowly that their occurrence cannot be detected in a measurable time. I venture to question this. Take the case of canesugar. Does anyone who has really worked with and learnt to appreciate this substance believe that any change would take place if the pure compound were dissolved in pure water and the solution were preserved in a clean vessel and no acid impurity were allowed to gain access to it ? And yet a trace of acid would almost immediately condition a perceptible change in such a solution. In solution, probably, the sugar is to some extent combined with water and certainly the water must be in intimate contact with its molecules: why then does not water act to an appreciable extent-why does acid produce such an effect? The dissociationists will answer :Because there are so few hydrogen ions free in water;* and that the acid acts by increasing the proportion of hydrogen ions. But to what extent can a trace of acid be supposed to have this result? Its effect is altogether out of proportion to the extent to which, ex hypothesi, it can be supposed to furnish hydrogen ions. Jan. 15, 1909 THE WIDE DISTRIBUTION OF SCANDIUM Up to the present scandium has been numbered amongst If it were concluded correctly from these facts that scandium is to be regarded as one of the rarest elements occurring on the earth, it would be all the more astonishing that outside the earth it undoubtedly occurs in other heavenly bodies in abundant quantities. Rowland, in the identification of the Fraunhofer lines of the sun's spectrum with those of known terrestrial elements, was able to detect with certainty some of the strongest scandium lines, and, moreover, the scandium lines appeared strongly in the spectrum of the sun. At the present time all the lines of this element, even the faintest, have been found with absolute certainty in the solar spectrum. Moreover, not only in the solar absorption spectrum, but also in the emission spectrum of the sun's atmosphere (flash spectrum), seen for a few seconds during total solar eclipses, the strongest scandium lines have been there. There can thus be no doubt that scandium is recognised amongst those of the few elements occurring present in relative abundance in the sun. The same is true of the stars. spectra it is found that the scandium lines appear plainly, By examining their and not only in those stars which resemble the sun. As the number of lines in its spectrum is large (Vogel's Spectral soon as a star has advanced so far in its development that Class I.a) the lines of scandium appear, generally very clearly. As an example, I may mention the star a-Persei, which has not yet reached the stage in which our sun now is. (Class III.a) which have long passed the state of the sun, Also in the red stars, e.g., a-Orionis and a-Herculis the scandium lines are still visible and unaltered. From the first it seemed clear to me that there cannot But it may be and I contend has been demonstrated that hydrogen ions are not the effective cause of hydrolysis-in fact, the selective action of enzymes is incompatible with the ionic explanation. The effects produced by enzymes are in all respects comparable with those produced by acids, so that if the action of acids be exercised not by the acid molecules as wholes but by hydrogen ions liberated from them in solution, enzymes, in like manner, might be supposed to contribute hydrogen ions, in which case, since acids generally act on cane-sugar, enzymes generally actually be this difference in the composition of the sun should effect its hydrolysis; in point of fact, however, only and stars on the one hand, and the earth on the other, as one enzyme is known which has the power (invertase). such a difference would contradict the cosmogonic theory, There is now abundant evidence to show that enzymes become associated with the particular substances which It is rather to be supposed that scandium occurs more which assumes a common origin of all the heavenly bodies. they hydrolyse and there is good reason to suppose that abundantly on the earth, if perhaps in a state of great they act by carrying water into the circuit of change, dilution, and sufficient search has not been made for this delivering it exactly where it is required to effect the break-element, or else it has been overlooked in analyses of down of the molecular complex. There is also good reason to suppose that acids act in a precisely similar manner as true catalysts. The effects produced by carriers, the use of which is so familiar to workers in organic chemistry, may be explained in a similar way. (To be continued). *The conclusion, based on Kohlrausch's observations, that there are free ions in pure water is quite illogical: the experiments do not justify it and it is impossible to admit that examined o ev r will be ure water has ever been minerals. analogous case of helium, which was long known to occur It is only necessary to call to mind the in the sun, but was not discovered on the earth till a much the stars, I observed the occurrence of the scandium lines, later date, owing to more refined methods of analysis. When therefore in 1901, in measuring the spectrum of I decided that I would go deeper into the question, and search for scandium on the earth by a spectrographic Exner and Haschek in their investigation of arc spectra (p. 145) have found ytterbium in Nilson's scandium, and I myself have found a not inappreciable amount of ytterbium and thorium in Cleve's scandium. method. As it was evident that this element would occur in a state of great dilution in the crust of the earth, I first tried to obtain information about the sensitiveness of the spectral reaction of scandium, so as not to work in vain. As I had no scandium at that time, after thorough practical study of the chemistry of the rare earths, I chose, to settle the question, one of those minerals which are known to contain scandium. When o'i grm. of the oxides of two different yttrotitanites (Nos. 247 and 248) were vaporised in the arc, both showed very plainly the principal scandium lines. They were also still plainly visible after I had diluted the oxides to one-tenth the strength with yttrium earths free from scandium, and again vaporised 01 grm. of this preparation. As according to Cleve the oxides of yttrotitanite contain o'005 per cent Sc2O3, the spectral reaction of scandium must be regarded as extraordinarily sensitive, even if the yttrotitanite oxides contain ten times as much scandium as Cleve states, which, according to my experience, seems to be the case. In any case, on the ground of this experiment, it seemed very promising to proceed to the spectrographic examination of minerals for scandium. I first used minerals in which, according to the experiments of Nilson and Cleve, scandium might be supposed to occur, euxenite (Nos. 214 and 217) and gadolinite (Nos. 226 and 227) without, however, detecting this element. This was the case when I examined a piece of gadolinite from Ytterby, most kindly sent to me by Dr. Benedicks (Upsala), but here I observed phenomena which surprised me, and which led me to perform further experiments. After three extractions of the very finely divided mineral, the unextracted part contained considerable amounts of alumina and beryllium earth. (All the gadolinites examined by me contained beryllium earth, in spite of the statements to the contrary in literature). Moreover, the scandium lines appeared in the arc not much fainter than in the part which had gone into solution, while the lines of the rare earths, and especially those of yttrium, had been much weakened. This behaviour of the unextracted part led me to suppose that the felspar-like matrix adhering to the gadolinite, which I had not removed in the working up of the mineral, and which cannot be extracted with acids, must be a silicate of alumina containing beryllium and scandium, for pure gadolinite would be completely extracted by the three processes. To test this supposition, I asked Dr. Benedicks for specimens of the matrix rocks of Ytterby gadolinite, and meanwhile investigated another beryllium alumina silicate, a smaragd (No. 25) which I happened to have. It contained easily detectable quantities of scandium, and, moreover, the other rocks found in the Ytterby mine, felspar, mica, and mica-schist, contained scandium, the last two to a considerable extent. Thus, for the first time it was proved that scandium might occur in other minerals as well as in those of the rare earths, and simultaneously the direction in which further search for scar.dium should be made was indicated. It was found that this element was present in a series of beryllium minerals and of micas. Among the micas tested, zinnwaldite from Zinnwald in the Ore Mountains contained specially large amounts of scandium, and when I examined whether other minerals from Zinnwald also contained scandium I found a great number contained this element, among them tinstone (SnO2) and wolframite, which occur in large quantities and are rich in scandium. But if micas contain scandium, rocks of which mica (especially biotite) forms an essential constituent, e.g., granite, gneiss, mica-schist, &c., must also contain scandium. This conclusion I also confirmed, thanks to the extraordinary spectral sensitiveness of scandium in the great majority of cases, and I now undertook the examination of as many different kinds of minerals and rocks as I could obtain from all possible places upon the earth, to see if they contained scandium, in order to acquire an adequate knowledge of the occurrence of this element, which had hitherto been thought to be so rare. | Before I give the results obtained I will make some remarks upon the details of the experiments. The minerals of the rare earths, especially the titanates, niobates, &c., give a spectrum which is so extraordinarily rich in lines that they must be worked up chemically before their spectra are photographed; i.e., must be decomposed into their chief constituents. (Prof. R. J. Meyer, Berlin, very kindly performed for me in his laboratory part of the very tedious and lengthy extraction processes. This renowned authority upon the chemistry of the rare earths often gave me valuable advice upon the further working up of the raw rare earths, and I am glad to take this opportunity of expressing my thanks to him). The part which could be extracted with acids was first separated from the non-extractive part, and the former was then further separated by treatment with oxalic acid into a part which was precipitated by this acid, and a part which was not precipitated by oxalic acid but gave a precipitate with ammonia. This precipitation of the remaining liquors with ammonia was always necessary, as scandium oxalate is exceedingly soluble even in weak mineral acids, such as the extraction always contains, and thus a part of the scandium remains in the liquid after precipitation with oxalic acid. The rare earths precipitated with oxalic acid were subjected to many other processes (precipitations, fractional crystallisations) to concentrate the scandium, but I will not now go into the details of these operations. The preparation of other minerals and rocks was essentially simpler. They were first finely powdered and then heated to a bright red heat for some time in a porcelain crucible to remove the gases and water contained in them. If this preliminary treatment is neglected unpowdered particles spirt with little explosions, and powdered pieces crumble up as soon as the arc is started. All preparations were vaporised with the same strength of current so as to obtain spectra under the same conditions, and a comparatively strong current was chosen 20 A. at 120 volts), because some minerals, e.g., quartz, zircon, bauxite, &c., are thoroughly vaporised only at high current strengths. The vaporisation is carried out in ordinary somewhat hollowed out arc lamp carbons, as with currents between 5 and 40 ampêres I could not, with the rods of far purer Acheson graphite given me by Prof. Muthmann (Munich), get anything but a very strongly hissing, unsteady, and easily interrupted arc. Two precautions are so important for taking the photographs that failure usually follows their neglect. First, large quantities of material (in my experiments about o5 grm.) must be vaporised, as scandium mostly occurs only in extremely small amounts in the minerals, and only when large amounts of material are used are its spectral lines visible (in the photographs. But when such large quantities of substance are vaporised on the arc carbon, generally a fairly bright continuous spectrum appears, which would completely mask the faint scandium lines. Therefore a spectrograph with very large dispersion must be used to efface the continuous spectrum sufficiently. I took the spectra with a concave grating apparatus of the observatory (Zeitschrift für Instrumentenkunde, 1905, xxv., p. 371) and by means of it could practically completely suppress the continuous spectrum. The second condition necessary for the success of the experiment is that the substance put in the arc carbon must be completely vaporised until all spectral lines disappear, which can easily be seen by observing the arc with a good pocket spectroscope. The vaporisation of rocks in the arc corresponds to a fractional distillation, the greater part of the most volatile constituents (e.g., the alkalis) vaporises at the beginning of the process, while most of the difficultly vaporised constituents, to which scandium belongs, vaporise quite at the end. If then a large quantity of mineral were put on to the arc carbon, and the photographs of the spectrum were taken as soon as a small portion or the substance had vaporised, no indication of the less volatile elements (e.g., Sc, Zr, Th, Ta) would be obtained in the resulting spectrum if they In 220 of these minerals the presence of rare earths was undetected, in 36 of these minerals the presence of rare earths was doubtful, and in 110 rare earths were detected. The chief result of the data given in the table is the surprising fact of the universal occurrence of scandium on the earth. In almost all rocks from which the mountains of the earth, or rather the chief parts of the earth's crust are formed scandium can be detected, and it is no longer a rare element, but, on the contrary, is widely and abundantly distributed, like only a very small number of other known elements. I am of the opinion that it would also be found in the rocks in which I did not find it, if larger quantities of material than I used were vaporised in the arc. From this proof of the universal distribution of scandium on the earth it is no longer strange, but natural, that it should be found everywhere in the stars and the sun. It may be of interest to mention that the meteoric stone of Pultusk, which to a certain extent forms a transition from the earth to the stars, contains a smaller amount of scandium than most of the earth's rocks which I investigated. Other conclusions may be drawn besides this important result. It is evident from the table, as was to be foreseen, that among the known minerals a true scandium ore, i.e., a mineral which contains scandium as an essential and not merely an accessory constituent, has not yet been found by me. On the other hand, it appears that scandium may occur in many different minerals, if it is not a necessary constituent. Those in which scandium is to be found most frequently are the zircon minerals, beryls, the titanates, niobates, and titanoniobates of the rare earths, tin stone, tungsten ores, and micas. The quantity of scandium in these minerals varies within wide limits, but with a few exceptions it is always so very small that chemical analysis can hardly detect it. The minerals which occur freely and which contain the most scandium are some euxenites and yttrotitanites, micas from the Ytterby mine, tin stone and wolframite from Zinnwald in the Ore Mountains. The last named mineral, according to a quantitative analysis by Prof. R. J. Meyer, confirmed spectrographically by me, contains about o 2 per cent Sc2O3; thus an amount which is at least ten times greater than that of euxenite and yttrotitanite, so that there is no longer any obstacle to the preparation of larger quantities of the element. There seems to be no rule about the occurrence of scandium in the minerals. When a large piece of gangue from Hitterö, which consisted of felspar, quartz, biotite, iron ore, orthite, gadolinite, malacon, thorite, was examined, I found scandium in the biotite and malacon, but not in the orthite, gadolinite, and thorite, which contain the rare earths, where it would be expected according to our former knowledge of the properties of this element. There seems, moreover, to be no rule about the occurrence of scandium in rocks. It is to be found in rocks of all possible chemical composition and petrographic constitution. The amount of scandium is also subject to considerable variations, but is always exceedingly small. In some cases the amount of scandium seems to be pro portional to the amount of mica which belongs to the essential constituents of the rock. This is the case, for example, with many granites. On the other hand, however, some mica schists have not as much scandium in them as would be expected according to this, and if garnets have separated the mica schist has become free from scandium and all the latter has gone into the garnets. The wide geographical distribution of minerals and rocks containing scandium indicates that there is no rule for the occurrence of scandium from a geological point of view. As a matter of fact it is immaterial for the occurrence of this element whether the rocks are of sedimentary, plutonic, or volcanic origin, and whether they were formed before the beginning of historical geology (archaic rocks) or at the present time (Vesuvius lava). The table contains rocks which were formed in the most different geological periods, although there is no apparent difference as regards the scandium. Also geological processes, such as endogenous and exogenous, contact metamorphosis, impregnation metamorphosis, pneumatolysis, are without apparent influence upon the occurrence of this interesting element. The same holds good of the neighbourhood of radio-active minerals, as the investigation of the minerals and rocks of Joachimsthal and Johanngeorgenstadt shows. All these negative results in the study of the laws regulating the occurrence of scandium, both from a mineralogical and geological point of view, indicate that scandium must be a very widely distributed element on the earth, like iron, which is found everywhere. It may be remarked here that the distribution of the rare earths seems to be exceedingly general. I have made observations on the occurrence of these elements in this research, and as lanthanum and yttrium have a very great spectral sensitiveness I have very often detected the rare earths, mostly with scandium. However, this last element may occur without the rare earths, and this is perhaps a support of Urbain's view, that scandium is not to be reckoned amongst the rare earths. For the chief characteristic of these elements is that they are always present simultaneously in numbers, if in relatively different quantities. No case is known in which one of the elements of this group occurs alone without being accompanied by at least one of the others, which is actually the case with scandium. After it has been found possible owing to the foregoing work to obtain larger quantities of scandium it is to be hoped that this element will be subjected to a thorough chemical and especially physicochemical investigation. (NOTE.-This investigation has meanwhile been begun by Prof. R. J. Meyer, with great success). I have repeatedly convinced myself in the course of the chemical preliminary operations for the above investigation that the chemical properties of scandium are only very imperfectly known, and that scandium must have many reactions which are not yet generally known. I have further examined the occurrence of large quantities of scandium in and near Zinnwald in the Ore Mountains, a research which has given results of great interest geologically and of general importance, but this investigation cannot be finished until I have collected a large series of rocks and minerals (which up to the present I have not been able to obtain). Hence the publication of the results so far obtained will be deferred till the research is finished. I have been enabled to carry through this investigation by the kindness of my late chief, Geheimrat Vogel, who procured me the means of obtaining research material, of Dr. Credner (Leipzig), and Dr. Benedicks (Upsala), who sent me some rocks and minerals which were of great value for my work. I offer them all my hearty thanks. -Sitzungsber. der K. Preuss. Akad. der Wissenschaften, xxxviii., 851, July 23, 1908. (NOTE.-While this article was in the press I heard of a Note (Proc. Royal Soc., London, lxxx., p. 516) by Sir William Crookes, who has recently prepared scandium from the very rare mineral wiikite). THE CORROSION OF IRON.* By ALLERTON S. CUSHMAN, known later as phthaleins. Phenolphthalein is a product which is formed by the condensation of two molecules of Assistant Director, Office of Public Roads, Dept. of Agriculture, U.S.A. phenol or carbolic acid with the anhydride of phthalic acid. (Continued from p. 17). The Action of Hydrogen Peroxide on Iron. PERHAPS the most conclusive proof that electrolytic action must take place before rusting can occur is given by an experiment of Moody's, which has been repeated and confirmed by the writer. Dunstan and his co-workers claimed that when iron is placed in hydrogen peroxide the metal is rapidly oxidised, with formation of ferric hydroxide. As Moody has pointed out, commercial hydrogen peroxide is invariably acid and contains impurities. In perfectly pure hydrogen peroxide bright iron will catalytically disengage oxygen and retain its polished surface unacted upon. It is not an easy matter to prepare a perfectly neutral pure solution of hydrogen peroxide, but it can be accomplished by two fractional distillations at 85° C. under reduced pressure (700 mm.) of commercial dioxygen. Before distilling the second time the solution should be made barely alkaline with a few drops of one-hundredth normal potassium hydroxide. In a pure neutral I per cent solution of hydrogen peroxide thus prepared, Moody's observation was confirmed. Iron immersed in the solution remained bright for a protracted period. Hydrogen ions do not exist in a pure neutral solution of peroxide; therefore neither solution of iron nor electrolysis can take place. If the flask containing the specimens covered by pure hydrogen peroxide solution is connected to a vacuum pump, oxygen is disengaged freely and boils off the surface of the metal without the appearance of the slightest speck of rust. Reduced to its simplest terms, the following explanation of the rusting and corrosion of iron seems to the writer the only one that is tenable. In order that rust should be formed iron must go into solution and hydrogen must be given off in the presence of oxygen or certain oxidising agents. This presumes electrolytic action, as every iron ion that appears at a certain spot demands the disappearance of a hydrogen ion at another, with a consequent formation of gaseous hydrogen. The gaseous hydrogen is rarely visible in the process of rusting, owing to the rather high solubility and great diffusive power of this element. Substances which increase the concentration of hydrogen ions, such as acids and acid salts, stimulate corrosion, while substances which increase the concentration of hydroxyl ions inhibit it. Chromic acid and its salts inhibit corrosion by producing a polarising or dampening effect which prevents the solution of iron and the separation of hydrogen. Demonstration of Electrolytic Action. Early in this investigation the writer observed that whenever a specimen of iron or steel is immersed in water or a dilute neutral solution of an electrolyte to which a few drops of phenolphthalein indicator had been added, a pink colour is developed. If the solution is allowed to stand perfectly quiet it will be noticed that the pink colour is confined to certain spots or nodes on the surface. The pink colour of the indicator is a proof of the presence of hydroxyl ions and thus indicates the negative poles. Many persons who are interested in the metallurgical problems connected with the iron and steel industry may not be familiar with the modern theory of indicators, and therefore an explanation of the manner in which phenolphthalein shows the presence of hydroxyl ions by the formation of a pink colour will not be out of place. Phthalic acid was first prepared by Laurent in 1836 by the oxidation of naphthalene, and was first called naphthalinic acid. It was afterwards shown that the compound was not directly related to the naphthalene structure, and Laurent changed the name to phthalic acid, the derivatives of which became Bulletin No. 30, U.S. Department of Agriculture, Office of Public Roads. It is in its nature so weak an acid that it is not dissociated in solution, and as the molecule is colourless, no colour is seen when it is added to a perfectly neutral solution. If, however, an alkali is added the corresponding salt of the weak acid is formed, which immediately dissociates with the formation of a colourless metallic cation and the strongly rose-coloured organic anion. Thus all hydroxides of basic elements will show the pink colour in solution, even when present in only the slightest excess. On this account phenolphthalein is an exceedingly delicate indicator of the presence of hydroxyl ions. Since phenolphthalein shows only the nodes where solution of iron and subsequent oxidation can not take place, Prof. W. H. Walker suggested the addition of a trace of potassium ferricyanide to the reacting solution, in order to furnish an indicator for the ferrous ions whose appearance mark the positive poles (see Note). If iron goes into solution, ferrous ions must appear, which, with ferricyanide, form the well-known Turnbull's blue compound. Going a step further, Walker suggested stiffening the reagent with gelatin and agar-agar, so as to prevent diffusion and preserve the effects produced. For this combined reagent, which indicates at one and the same time the appearance of hydroxyl and ferrous ions at opposite poles, the writer has suggested for the sake of brevity the name "ferroxyl." The reagent is prepared and used in the following manner :-A hot solution of the purest agaragar or gelatin in distilled water is carefully neutralised with one-hundredth normal potassium hydroxide, using phenolphthalein as the indicator. When exact neutrality has been obtained a few drops of a dilute solution of potassium ferricyanide is added. When a layer of the reagent is poured into a dry Petri dish floating in ice water it should stiffen into a firm jelly in a few minutes. The polished specimens are laid carefully on the jelly and flooded with another layer of the reagent. After the preparation has hardened it should be covered and set away in a cool, dark place. In the course of a few hours the negative and positive zones will begin to develop in red and blue. If the reagent has been properly prepared the colour effects are strong and beautiful. In the course of a few days the maximum degree of beauty in the colours is obtained, after which gradual deterioration sets in. (NOTE.-Phenolphthalein is used to a large extent in empirical tests, as in dairying, the cement industry, soil examinations, &c. The name is cumbrous if not alarming to the layman, while the chemist does not need to be reminded of the origin of the compound each time he has occasion to speak of it. A shortening of the name of the indicator to "phenolin" would be a decided improvement). In the pink zones, as would naturally be expected, the iron remains quite bright as long as the pink colour persists. In the blue zones the iron passes into solution and continually oxidises, with a resulting formation of rust. Even the purest iron develops the nodes in the ferroxyl indicator, but impure and badly segregated metal develops the colours with greater rapidity and with bolder outlines. This result would of course be expected, as in pure iron the formation of poles would be conditioned by a much more delicate equilibrium than in impure iron, where changes in concentration of the dissolved impurities would stimulate the electrolytic effects. Even so-called chemically pure iron contains small quantities of dissolved gases, and it is not improbable that even slight variations in the physical homogeneity of pure iron will occasion the electrolytic effects which are made visible by this delicate reagent. It has been noted by a number of investigators that different samples of iron and steel do not rust in the same way when subjected to the action of water and air. While some samples show localised electrolytic action, as indicated by deep pitting, others become covered with a more or less homogeneous coating of hydroxide, which |