NEW BOOKS The Silver Bromide Grain of Photographk Emulsions. B y A . P. H . Trznelli and S. E. S h e p p a r d 22 X 15 cm; p p . 113. New York: D . Van Nostrand Co., 1921. Price: $25o.-This is the first of B series of monographs on the theory of photography which the Research Laboratory of the Eastman Kodak Company is going to write. The nest two volumes are t o be on gelatine and the fourth on the theory of development. This is an admirable thing to do and should mark the beginning of a new period in the science of photography. In the monograph the chapters are entitled: the influence of ammonia on photographic emulsions and a theory of ripening; von Weimarn’s theory and the determination of the dispersion of silver bromide precipitates; accessory factors influencing the dispersity of silver bromide emulsions; crystallization catalysiq; capillarity and crystalline growth ; experimental study of the crystallization of qilver bromide; the classification of silver halide crystals ; the silver bromide crystals of photographic emulsions; the directions of most rapid growth in silver bromide crystals, and the occurrence of anomalous forms; the behavior of silver bromide and silver iodo-bromide crystals in polarized light. When silver bromide plate4 are treated with ammonia vapor, they become more transparent, apparently owing to the formation of a silver bromide ammonia compound having approximately the same index of refraction as the gelatine. No independent proof of this is given, though a reference is made, p. 25, to Ephraim’s work. Ammonia also causes an increase in the size of the grains but does not cause development except for long exposures. The authors believe that under the combined action of ammonia and gelatine silver bromide may be reduced somewhat with production of colloidal silver. The authors apparently consider that optical sensitizers act by resonance, p. 50. “The operation of a sensitizer may be regarded in respect of either wave length or phase. It would be very possible for a crystalline substance t o absorb only a limited amount of light of suitable wave-length, b u t of such irregular phase ordering that the equilibrium radiation field of the crystal would get only partially in resonance. We can conceive then that a non-crystalline body in solid solution or absorbed would increase the photochemical sensitiveness, acting as a resonance complement. Thus colloidal silver acts as a panchromatic sensitizer for silver halides. The behavior of traces of calcium, bismuth, etc., in developing phosphorescence in the alkaline earth sulphides is a similar case. If the above conception is true, it is possible that silver iodide acts both as a wavelength sensitizer and as a phase-sensitizer for silver bromide, as well as acting as an independent source of nuclei by its direct photolysis.” On p. 100 the authors say that “the forms of the silver bromide crystals in photographic emulsions are very varied, though all belong t o the same crystallographic system [regular] and the same class [dyakisdodecahedral]. In 122 different emulsions which were examined a t a magnification of 2500 diameters, The presence of cubes and of only octahedra could be positively identified. . . combinations of cubes with octahedra or other forms could never be determined.
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From ammoniacal solutions silver iodide is precipitated in the metastable, regular form, which is isomorphous with silver bromide.” The book is an interesting one and contains somc remarkable photographs of silver bromide crystals; but it is a little puzzling t o know just what the scope OF the book was meant to be. What one would have liked would have been a theory of ripening and one is left with an uneasy feeling that the authors think that they have given one. I t is possible that they have; but the reviewer has read the book three times already without learning what it is. Some of the difficulties to the reader may be illustrated by the following paragraph which is said to sum up the fundamental relation existing between photochemical catalysts, positive and negative, and crystallization catalysts, p. 51. “Crystallization is a process of approach to a complete (static) equilibrium of the radiation fields (chemical affinities) of the component atoms and constituent molecules. The attainment of static equilibrium may be accelerated or retarded by alien substances, or crystallization catalysts, which, from the actino-chemical nature of crystallization, are consequently likely t o be also photochemical catalysts, affecting the transformation and redistribution of catalytic light energy.” Wilder D . Bancroft Qualitative Chemical Analysis. B y M. Cannon Sneed. 2r X 14 cm; 198. New York: Ginn and Company, 1921. Price: $~.~o.--Theauthor believes that a course in qualitative analysis “should serve as a means of reviewing, fixing in the mind of the student, and extending his knowledge of the principles OF general chemistry. On the experimental side its aim should be to train the beginner t o acquire methods of careful manipulation and to do exact, dependable, and intelligent work. To this end an attempt has been made t o present the experimental exercises in a concise form and to give laws and theories in such a way that the student may understand and correctly interpret his observations. ” The chapters are entitled: introduction; gases, solution, and the theory of electrolytic dissociation; physical and chemical equilibrium and Group V; ionic equilibrium treated quantitatively and Group IV; hydrolysis, amphoterism, oxidation and reduction, and Group 111; precipitation of hydrogen sulphide, complex ions, colloidal condition, and Group 11; Group I ; the anions; the systematic analysis of an unknown. There is a great deal of physical chemistry in this book and the question is whether this is a good thing or a bad thing. The reviewer does not quite see what the gas laws, quantitative ionic equilibrium, and amphoterism have to do with qualitative analysis. Even supposing they are essential, should they be taught here or somewhere else? It seems t o the reviewer that either the book presupposes a lack of co-ordination at the University of Minnesota or else that the author wishes to present the subject of qualitative analysis as complete in itself-which comes to the same thing and is apparently hard on the stitdent. On p. 10 the author introduces the term “diffiision pressure” in what seems to be a neu and undesirable sense. Wildvr D. Bancroft
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Elementary Qualitative Analysis of the Metals and Acid Radicals. B y 143. New York: D. Van Nostrand Go., 19 X 13 cm; p p . aii
F. C. Reeve.
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1921. Price: $1.5o.-This book claims to present the subject of elementary qualitative analysis in such a way as to interest the high school student. The aim of the author has been: to present the main scheme of analysis without the complication of special contiitions; to give working directions for each test rather than its description; and to write the chemical equations for all reactionr. The reviewer is not qualified to tell what will interest a high school student. There are one or two points which interested him as a chemist. On p. 2 the author says that addition of small amounts of an acid, a base, or a salt makes water a conductor. The electrolyte does not increase the conductance of water. It would apparently have been just as simple and certainly more accurate to say that the solution conducts instead of saying that the water conducts. On p. 16 the author says that ammonia reacts with lead chloride to form basic lead chloride, PbCl(0H). Is there any reason beyond a desire for simplification why basic lead chloride should not be PbChH2.PbC127 On p. 20 there is the very interesting statement that the filtration of silver chloride can usually be made easy by “the addition of a number of crystals of ammonium nitrate and the application of gentle heat to the mixture before filtraYion.” Very few chemists could tell why this addition is effective and it is rather a pity that no explanation is given. I t is not desirable that a student should follow directions blindly. On p. 37 the student is told to “acidulate 5 cc of a solution of copper nitrate or other copper salt with a few drops of dilute hydrochloric acid. Add two or three small iron nails to this solution and gently warm it. In a few moments the iron nails will be covered with a coating of metallic copper.” This would seem to be the worst possible way of doing the experiment because there will certainly be a formation of cuprous chloride which must complicate matters, and to which no reference is made in the equation. These few comments are not intended in disparagement of the book, which is doubtless an admirable one. They do show how difficult it is to write anyWilder D. Bancroft thing clearly, simply, and accurately.
Red-Lead and how to use it in Paint.
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By A . H. Sabin. Third edition.
19 X 13 cm; p p . x i 139. New York: John Wiley and Sons, 1920. Price: $z.oo.--In. the preface the author says that in the last few years there has been a great increase of interest in the subject of red-lead paint; “due, no doubt, t o the rise in the cost of bridges and other metal structures, which makes their preservation more important; this incidentally leads t o more discussion of it in the meetings of engineers; and partly to the comparatively recent introduction of red lead in paste form, which, as is explained in the text, is made possible by improvements in the pigment, and increases its availability for more extensive use. The writer is willing t o predict that the next step will be its sale as a liquid paint, ready for use; and that this will so much promote its use as a finishing coat and for general repainting, that the demand for it will be several times as much as now; perhaps will equal that for white lead. Holding this belief, which is based on thirty years’ experience and study of protective coatings, the writer has tried to give information as t o the character of these liquid paints; for all paint must be reduced t o this form before it can be applied.” The author discusses briefly the manufacture of litharge, red lead, and orange mineral; gives a very cursory statement of the objections to red lead;
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and points out that a certain brand of red lead contains less than two percent of litharge and is a very superior product. I n certain cases the presence of litharge is an advantage, it being added when the paint is t o be applied t o the interior of stand-pipes and conduits, because it makes a harder film which is not softened so much by the water with which it is continually in contact. Lampblack i n paste form can be mixed easily with red lead; but there is a p t t o be difficulty if one uses dry lampblack. When considering how much pigment is needed, p. 25, the author says “that there must be some proportion of oil and pigment which gives most durability. If too much oil is added, we finally get a film which is essentially an oil film, much less durable than a paint, and less impervious to air and moisture. If we add too much pigment, we make a paste which, though fluid, is too viscid [ ? ] for a paint; still more pigment makes putty which is not a fluid a t all, but a plastic solid; it has uses but it is not paint.” The author answers the question himself by saying that 33 pounds of red lead t o a gallon of oil, plus what turpentine seems desirable, is satisfactory. Speaking of mixed pigments, p. 37, the author says that “while no one should pretend t h a t the particular paint he fancies is the only one which has any merit, i t is not likely t h a t for durability, or the protection of metal from corrosion, a mixture of pigments is ever better than a single one, except in cases where a n inferior paint is improved by the addition of a better one; that is, a good paint is not made better by being mixed with a worse. And yet there are people who admit that silica, for example, made by itself with oil into a paint, is worthless, either as t o durability or anything else, but who maintain t h a t 30 to 40 percent [by volume] of such paint may profitably be added to a red-lead paint.” The latter part of the book is devoted t o specifications for painting and t o methods of analysis. As the quotations indicate, the book is interesting reading. The only drawback to it is that it is obviously a n advertising pamphlet put out in book form; but with no attempt a t a non-partisan, scientific presentation of the subject. It is a pity that the author should have done this; but he probably had reasons Wilder D. Bancroft for his course which satisfied him.
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485. LonThe Electric Furnace. By J . N . Pring. 2 2 X 14 cm; p p . xii don and New York: Longmans, Green and Co., 1921. Price: $Io.go.-This is a book that should have been written by a n American. Excellent as the book is, i t omits two important developments of electric furnace service that have been brought t o their present state by American engineers-namely, brass melting and heat treating. But even in a much larger sense the real success of the electric furnace has been the work of Americans. Its history follows fairly close t o that of the many processes that were laboratory experiments or commercial installations on a small scale abroad, and really came into their true worth on being brought to this country. A notable instance of that was the Bessemer steel method, where the first American improvement, by Holley, added 50% in output and others following in rapid order made a total gain of several hundred percent. The discovery and partial development abroad of the electric furnace
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was merely the opening chapter of its history. The American engineer, with his fine disregard for classical traditions and his eager desire t o do things in a better way for a bigger output, in which he is amply justified by his skill and ingenuity, takes hold of the admittedly imperfect foreign design and turns it into a tool to be used with confidence. A striking proof of this is found in this book. Taking at random 100 consecutive pages (e. g., pages 259 to 358) there are 59 technical references of which 32 are to American sources. There can be little adverse criticism of a book like this; prepared with great care, written in very good style, well printed on better paper than some we have recently seen, plenty of excellent illustrations, and with a very good bibliography. I t will be found equally a t home with the practical engineer or in the classroom of technical schools. It might be better for its American edition had some of its cost-data been reduced to United States figures, but as these figures, in the present state of exchange are exceedingly relative, the criticism is rather captious. R. R. Reed
The Emission of Electricity from Hot Bodies. B y 0. W . Richardson. Second edition. 22 X 15 cm; p p . vii 320. New York and London: Longnaans, Green und Cu., 1921. Price: $s.zs.-The subject is presented under the following headings: mainly considerations of a general character; theory of the emission of electrons from hot bodies; temperature variation of electron emission; the effect of gases on the emission of electrons; energetics of electron emission; the emission of positive ions by hot metals; the effect of gases on the liberation of positive ions by hot metals; the emission of ions by heated salts; ionization and chemical action. While the whole subject is a fascinating one, there are certain portions of the book which are of esceptional interest to the chemist and it will therefore be well to concentrate on them. The most important of these is the section dealing with the question of contact potential, p. 41. “There is a n intimate connection between the rate of emission of electrons from different substances and their contact differences of potential, This can be shown very simply by considering the case of a n insulating evacuated enclosure containing two bodies, A and B, of different materials maintained a t the uniform temperature T. The electrons emitted by A will ultimately either return to A or reach B, and vice versa. Now suppose that both A and B are uncharged initially, and that A emits electrons a t a faster rate than B. The greater rate of loss of negative electrons by A will cause A to acquire a positive potential relative to that of B. This difference ofpotential will not increase indefinitely because the electric field thus set up will tend to stop the transference of electrons from A t o B. A steady condition will finally be established in which each of the bodies A and B receives in a given time as many electrons as it emits in that time. This condition is also characterized by the occurrence of a constant difference of potential V between any two points close to the surfaces of A and B, respectively. The numher of electrons in unit volume of the space will then vary from point to point, but will not change with time. A consideration of the nature and number of the variables entering into the equations governing the equilibrium of the electrons shows that V is independent of the size, shape and relative position of the bodies A and B, and depends only on their nature and the temperature T. This result holds true both on the basis of the classical dynamics and on that of the quantum theory. The difference Of
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potential V is, therefore, the intrinsic contact potential difference of the bodies A and B at the temperature T.” “ I t follows from equation (35) that the relative powers of electronic emission of different bodies a t a given temperature will be determined by their contact differences of potential; so that whether bodies show much or little difference one from another in the former respect will depend on the magnitude of the latter quality. There is still a great difference of opinion as t o the magnitude of the contact difference of potential between metals whose surfaces are free from gas and in a good vacuum. The school which attributes these differences of potential to chemical action between metals and the surrounding atmosphere holds that under the conditions referred to the contact potentials would completely disappear. If this view is correct we should expect all hot metals t o give nearly equal thermionic currents per unit area a t any given temperature, provided they were in a perfect vacuum and their surfaces were uncontaminated. The opposite school regards these potential differences as an intrinsic property of the metals affected and considers the changes caused by gases and other contaminating agents to be of a secondary character. From this standpoint we should expect t o find potential differences between metals in a good vacuum of the same order of magnitude as those observed in a gaseous atmosphere. The advocates of these opposing views have waged an intermittent warfare for a century without coming t o a definite settlement. “Until recently most investigators who have attempted t o decide this question experimentally have concluded that their results favoured the chemical theory. In 1912 the writer pointed out that none of these experiments were conclusive, all the observed phenomena being explicable on the intrinsic theory when due account was taken of various secondary actions which were bound to occur under the conditions of the experiments. Quite recently a considerable amount of evidence favouring the intrinsic theory has accumulated. Thus Richardson and Compton examined the photoelectric currents obtained when monochromatic light fell on small discs of various metals placed a t the centre of a large spherical electrode. With this arrangement the saturation value of the current should be reached when there is no difference of potential between the two electrodes. This was found t o be the case if the contact potentials were included among the potential differences operative. Somewhat similar experiments have been made by Page. I n all these experiments good vacuum conditions were attained. In addition, in Richardson and Compton’s experiments with sodium, and in all Page’s experiments, the metal surfaces tested were cut mechanically in vacuo. Still more recently the contact difference of potential has been measured directly under the best vacuum conditions with surfaces machined in vacuo by A. E. Hennings, who finds that the potential differences are still of the order usually observed, the metals being more electropositive when freshly cut. All these experiments support the intrinsic potential theory, although there is abundant evidence that gases produce definite and complicated changes in the observed values. On the other -hand, Hughes, working with surfaces of metals freshly distilled in vacuo, found the metals t o be initially most electronegative and to become more electropositive under the action of small quantities of air. Millikan and Souder, also, have found that surfaces of sodium are most electronegative when freshly cut and become more electropositive on oxidation. It is clear that
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the experimental evidence as to the origin of contact potential differences is still conflicting, but the balance would seem to favour the view that it is due to a n intrinsic property of the materials and not to surface films of foreign matter.” Fredenhagen believes that the emission electrons from Wehnelt cathodeshot metal cathodes coated with lime or baryta-is a secondary effect, arising from the recombination of the earth metal with the oxygen liberated by electrolysis during the passage of the current through the oxide. This view is not shared by the author, p. 101. “Taking all the evidence together it seems to the writer that the view which attributes the emission from metallic oxides to the escape, owing to increased kinetic energy, of those electrons which give rise to the electrical conductivity of such materials has much more to be said for it than any other so far put forward. This position is strengthened by the recent experiments of Germershausen, who has shown that the removal of the last traces of gas from a Wehnelt cathode and its surroundings increases the emission from it. Under these conditions the discharge from the lime becomes very steady and shows temperature and voltage characteristics similar to those exhibited by tungsten filaments under the best vacuum conditions. “In recent years oxide-coated cathodes have been very thoroughly studied in the Research Laboratory of the American Telephone and Western Electric Companies. One result of these researches has been to establish thoroughly the view that the emission from such cathodes iq an intrinsic property of the oxide similar to the emission from pure metals and is not a secondary phenomenon due to chemical action, bombardment of the cathode by positive ions, or the like. Tests have shown that the oxycathodes maintain their emitting power unimpaired in vacuo in which the measured pressures were as low as to mm. Filaments have been maintained in operation for such long periods that the mass of the electrons emitted by them exceeded fifteen times the mass of the oxide coating. I t appears that the value of b for filaments coated with a mixture of the oxides of barium, strontium, and calcium is much less than that for a pure lime filament and their emitting power at a given temperature is correspondingly greater. The value of b deduced from the temperature variation of the emission is very close to the value deduced from the cooling effect. Direct tests by Davisson and Germer show that any electron emission which may be due t o positive ion bombardment must in general under the conditions in which the tubes are operated be upder one ten-thousandth of the total emission and such effects can therefore play no important part in the phenomena. Very interesting experiments have been made with filaments coated with oxide evaporated from a second oxidecoated filament. It appears that exceedingly small amounts of the oxide (enough to cover the underlying metal to about 30 percent of its area with a layer of oxide one molecule deep) are sufficient to increase the emission from the value appropriate to the pure metal to that characteristic of the oxide. This corresponds t o an increase in the current by a factor of about I O 9 under the conditions of the experiments. The variation of the emission with the amount of oxide deposited has been investigated. It is found that for very minute deposits the emission practically remains a t the value for the pure metal, as the deposit increases the emission begins to rise rapidly in two steps to a maximum value after which it falls with similar rapidity to the value characteristic of a thick oxide layer. Up
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t o heyond the maximum the emission can be represented as the sum of two terms of the form Cxnez/awhen C, n and a are constants and CE is the amount deposited. The drop in the emission over the falling part beyond the maximum appears to be due to a drop in the value of A from that for the pure metal t o the smaller value appropriate to the oxide, the other constant b in the emission formula remaining unaltered. Apparently the thinnest deposit has already established the value of b appropriate to the oxide.” Working with platinum wires which had not been heated in hydrogen for a long period, Wilson found that the emission varied with the pressure of the hydrogen, whereas Richardson found that the emission from a platinum wire in hydrogen is practically constant when the pressure varies from one millimeter to 0.001 mm, p. 119. “It is clear from the facts which have been described that the emission from platinurn in a n atmosphere of hydrogen shows two quite distinct types of behaviour, under conditions which a t first sight appear to he identical. The cause of this diflerence was investigated by Wilson who found that the conclition in which the emission was sensitive t o changes in the pressure of the hydrogen occurred only with ‘fresh’ wires, that is to say, with wires which had not been heated in hydrogen for any considerable length of time. The condition of insensitiveness to change of pressure, on the other hand, was found to be characteristic of wires whichhad been subjected to continued heating in hydrogen. Such wires may, for brevity, be described by the term ‘old.’ Wilson has pointed out that the observed facts are consistent with the view that in a fresh wire the hydrogen exists in a state of solution, whereas in an old wire most OF it is present in the form of a compound which is formed with extreme slowness. The essential difference between solution and chemical combination lies in the fact that the amount of gas dissolved is a continuous function of the external pressure, whereas the amount chemically combined, once the reaction has been completed, is constant, if the external pressure exceeds the dissociation pressure, or zero if the pressure is below that value. Since the amount of hydrogen present in the wire is .held to determine the value of the emission a t a given temperature, on this view the emission will only be a continuous function of the pressure of the external hydrogen with fresh wires, in which the gas is present in the dissolved state. The dissociation pressure of the hydrogen compound must be very small (under 0.001 mm.) a t the temperature of the experiments referred to (up to 1400’ C), since the large emission from a n old wire could not be removed by pumping. However, dissociation pressures vary rapidly with temperature, and Wilson has found that the large emission from an old wire can be ‘pumped odt’ if the temperature is raised to about 1700’ C. This view is also substantiated by the fact that the large emission from a n old wire can be ‘burnt out’ almost instantaneously in an atmosphere of oxygen a t much lower temperatures; since the pressure of hydrogen in equilibrium with water vapour and its dissociation products under the conditions of such an experiment is very low. It is, however, possible that the burning out process contaminates the platinum surface and reduces the emission to a value less than that which would characterize a clean platinum surface.” There are some curious things about the emission of ions by heated salts, p. 261. “The phenomena exhibited by cadmium iodide have been examined in some detail by Sheard, who tested both the conductivity and the emission of ions from the salt. A t temperatures below the melting-point of the salt (400’ C) the
New Books saturation currents in the vapour decayed continuously from a maximum initial value, in agreement with Schmidt’s results. At higher temperatures there was a rise to a maximum in about 15 minutes followed by a slower decay. The currents due to the emission of ions from the heated salt showed a different behaviour from those in the vapour. A t 470’ C, for example, there was a n enormous negative emission which decayed very rapidly with time. The positive emission was a t first too small to measure, but it gradually increased t o a maximum value in 90 minutes and then fell away. A t this stage the positive emission was greater than the negative, but the greatest positive emission was less than one twohundredth part of the large negative emission observed on first heating. A similar but less marked contrast between the positive and negative emissions was observed when iodine was similarly tested. Sheard also examined the behaviour of the salt which distilled out of the experimental tube in successive experiments. He found that the first distillate gave a small negative and a large positive emission whereas the second showed the contrary behaviour. In all the distillates there was a great disparity in the magnitudes of the positive and negative emissions; and in almost every case the distillate from a preparation which gave a large negative and a small positive emission, or vice versa, showed the contrary behaviour. The currents from all the distillates were much smaller than the large initial emission from the fresh salt, The distilled salt showed no appreciable change in appearance, but chemical analysis showed that successive distillation reduced the percentage of iodine, “There can he little doubt that these interesting time changes in the emission of ions from salts and in the conductivity of salt vapours are symptomatic of the occurrence of chemical changes; but it is very difficult to form a definite opinion as to what the precise nature of the change is, in any particular case. When the currents are increasing with time it seems fairly clear that a substance possessing greater thermionic activity is being formed and when the currents are diminishing the resulting products are less active in this respect. One difficulty in forming a judgment as to the nature of the chemical changes arises from the delicacy of the electrical test. This is so sensitive that the amount of matter concernedmight often be incapable of detection by chemical methods. It is also possible that many of the effectsare due to the occurrence of unstable forms which are not persistent enough to be recognized by chemical methods. This is especially likely since the time changes show that the bodies concerned have Only a transitory existence. In many cases these time changes are attributable to the presence of contaminants. Thus ordinary laboratory specimens of ‘pure’ aluminum phosphate give an initial emission which is large compared with that from the pure salt and which after a time falls to a small value. Horton has shown by spectroscopic examination that this decay in the emission is accompanied by the disappearance of sodium salts. “The complicated phenomena in the case of cadmium iodide have been studied more fully, perhaps, than those shown by any other salt, and here it doe? seem possible to form, a t any rate, a limited judgment as to the nature of the phenomenon from the chemical side. Schmidt has ventured the opinion that the time changes in the vapour arise from the decomposition of the molecules of CdIr into C d + + and Iz-- with a subsequent interchange resulting in Cd+- and I z f - , that is to say, two neutral molecules. It does not seem to the writer, however,
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that any theory of this type will account for the observed time changes in the vapour in presence of an excess of salt. So long as there is any excess of salt the vapour will be supplied a t a steady rate and the phenomena observed in it should oe independent of time until the salt disappears. It is necessary to suppose that the actions in the vapour are not conditioned solely by the amount of CdIz vapour ,resent but rather by some other substance coming from the salt. The time :hanges must in fact be conditioned by something the amount of which is deternined by actions occurring a t the salt and not simply by a decomposition of :admium iodide vapour. In one respect this question has been definitely settled iy Kalandyk who has shown that the currents in cadmium iodide vapour under the .onditions of these experiments are independent of the time, provided every trace I f water is removed from the salt and from the apparatus. The way in which vater brings about the time changes usually observed is unknown. Kalandyk’s :xperiments only tell us that there are no timechanges when water is absent, they io not offer an explanation of the changes which occur in the presence of water or rater vapour. Sheard’s results point to the conclusion that the large negative nitial emission, when it is present, is connected with the liberation of iodine. On his view the smaller negative emission from the distillates would be related t o the educed iodine content of the salt, which after distillation probably consists of a olution of an unrecognized subiodide of cadmium in CdI2. The presence of the ubiodide would reduce the equilibrium pressure of iodine in presence of cadmium odide vapour. The probable existence of a subiodide of cadmium is distinctly ndicated by the work of Morse and Jones who succeeded in isolating a iody having the composition Cd&, probably a solution of the subiodide in
:din." The behavior of quinine sulphate is apparently not what LeBon thought it vas, p. 304. “The ionization, discovered by LeBos, which accompanies the iydration and dehydration of certain crystals has frequently been attributed to hemical action. The case which has attracted most attention is that of quinine ulphate. This substance, when allowed t o cool after heating to a certain high emperature, phosphoresces and causes the surrounding gas to become conducting. diss Gates showed that the ionization was not caused by rays capable of penerating the thinnest aluminum foil. She also found that the current from the alt was greater when it was positively than when it was negatively charged and hat the hydration of a given amount of salt caused a greater conductivity than he dehydration. These results were confirmed by Kalaehne, who concluded, in ddition, that the hydration of a given amount of the salt a t a fixed temperature berated a constant quantity of electricity independently of the rate of hydration, lthough the actual instantaneous currents depend very considerably on the rate f hydration. Recent experiments by deBroglie and Brizard suggest that in all lese cases the ionization is only an indirect effect of the absorption or liberation of rater vapour. Both the ionization and the luminosity observed with the sulhates of quinine and cinchonine seem to be due to minute sparks arising from the iboluminescence of the crystals of these substances which takes place during ydration and dehydration. Although it is almost impossible to saturate the irrents from these substances the ions have a high coefficient of re-combination. ‘0th the ionization and the scintillations increase as the pressure is reduced from Wilder D. Bancroft tmospheric.”
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Elementary Chemical Microscopy. By &nile Monnin Chamot. Seconc; edition. 23 X 15 cm; pp. xv 479. New York: John Wdey and Sons, 1921 Price: &.z~.-The first edition was reviewed six years ago (20, 175). A t thai
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time the reviewer was able to bear witness from first-hand knowledge of the im. portance of the microscope in the study of alloys. Quite recently Mr. Chamot’s as. sistant has cleared up with only six month’s work the whole question of the bluc colors and the metallic colors in birds’ feathers. When one remembers that mer like Rayleigh and Michelson have worked a t this problem without settling it this must be considered a triumph for chemical microscopy. There will never bc any doubt as to the value of the microscope to the chemist in the minds of thosc who are privileged t o know the remarkable work on primers done by Mr. Chamoi during the war. The same statement is made in a very modest way in the preface “The Great War brought us face to face with a multitude of intricatejndustria and economic problems, in the solution of which the chemist was not slow t c appreciate the importance and the value of industrial chemical microscopy It is probable that a greater number of new applications of microscopic methodl were made in our industries than in the entire preceding quarter of a century.” According to the author the changes in the new edition “have been chieflj in the rearrangement of the chapters, in the elaboration of the data presented and in the rewriting of obscure passages. Comparatively little new apparatu! has been described or new methods introduced.” I n the appendix is a brie synopsis of the course in Introductory Chemical Microscopy as now given in thc Department of Chemistry a t Cornel1 University. The subject is now presented under the following headings: objectives ant oculars; illumination of objectives and illuminating devices; microscopes for use ii chemical laboratories; vertical illuminators and metallurgical microscopes ultramicroscopes and apparatus for the study of ultramicroscopic particles useful microscope accessories, laboratory equipment, work tables, and radiants micrometry and micrometric methods; quantitative analysis by means of thl microscope; the determination of melting and subliming points ; the determinatioi of refractive index by means of the microscope; crystals under the microscope methods for handling small amounts of material; the methods of microchemica qualitative analysis; characteristic microchemical reactions of the commoi elements and acids when in simple mixtures; preparing opaque objects for t h microscopic study of internal structure; appendix. The reviewer was interested in the statement, p. 310, that “in the micro chemical examination of rock sections, aluminum hydroxide can be stained wit1 Congo red and gelatinous silica with malachite green-tests which may be em ployed in testing for ‘weathering,’ etc.” Off-hand one would have expected ai acid dye t o haye worked better with alumina than a substantive dye. Wilder D.Bancroft BRRATUM
The price of Gildemeister and Hoffmann’s *‘The Volatile Oils” is $10 pe volume and not $7.50 as stated (25, 762).
