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to emphasise his point, is apt at times to state his

OUR BOOK SHELF. case too strongly.

Traité d'Exploitation commerciale des Bois. By A. We cannot by taking thought dispel disease; the

Mathey. Tome i. Pp. xviii +488. (Paris : Lucien influence of the patient's mind over his body is

Lavens, 1906.) Price 15 francs.

This volume will rank high among the many excelpowerful, but is it “ almost all-powerful ”? The

lent Continental books which deal with forest utilisaconsumptive patient is usually full of hopefulness to tion. The author gives a great amount of important the last, but unless other means are taken to promote and practical information concerning the commercial recovery his light-heartedness is of little avail. The exploitation of timber from every possible point of writer later greatly modifies his original statement

view. The work is profusely illustrated by well

drawn and excellently reproduced figures, numbering regarding the influence of mind over body by stating

no fewer than 377, and to these must be added eight (p. 29) that “there are many diseases not cured by

beautiful chromo-lithographic plates. The volume is the mind alone”; in fact, he might add that quite divided into five parts. few' maladies can be so treated. Nevertheless, we Part i, deals with the general properties of wood. agree with the statement that “in every case of The anatomical features are also described. The disease the condition of the mind is an important

macroscopic characteristics of the various home and

exotic deciduous and coniferous species are gone into, factor."

and the diagnostic features are brought out very We cannot concur with the writer's distinction

clearly by an excellent series of figures, which show between “madness” and hysteria” (p. 21).

specimen blocks of the various woods cut in transHysteria is a disease with definite physical symptoms, and longitudinal sections. The and, in addition, the patient exhibits some mental chemical and physical properties of timber are treated aberration. Now if this mental disturbance becomes in detail. This part finishes with an excellent account

of the effect of soil and climate on the growth and more marked, the patient is usually considered to have

texture of the wood. passed from the realm of physical disease into a state

Part ii. deals principally with defects in timber, commonly spoken of as “ madness," and yet the

such as abnormality of growth, knots and wounds of disease is the same in both cases, only in one instance all kinds, which may be caused by physical agencies. the physical symptoms are the more prominent and in The different kinds of rot arising from the attack of the other the psychical. Dr. Schofield writes that “a

fungi are exhaustively dealt with. This part is

extremely well illustrated by means of the coloured person whose conscious mind is unsound is suffering

plates already referred to, which should greatly facilifrom madness: one whose unconscious mind alone

tate the recognition of these maladies that are only has gone astray suffers from neuromimesis

too frequently ignored in this country. The various hysteria; and the distinction is good.” Now a few forms of white and red rot being due to specific pages previously the writer tells us that “there is but organisms greatly increases the danger of sound one mind.” Clearly, then, the mind is either sound timber being contaminated by diseased timber; hence or unsound, for the whole cannot be what a part of

the importance of recognising those diseases in order, it is not. Further, we are told that “the recovery of

if possible, to prevent their future occurrence and

spread. the patient from disease depends more upon the Part üi. of the work deals fully with the important efficiency of the vis medicatrix naturae, in other subject of seasoning and storing timber, and the words, unconscious mind, than upon any other agent." different artificial methods of rendering wood antiTherefore it would appear that in hysteria the septic by means of immersion in, and injection with, apparatus which is all-powerful in cure is itself

the various kinds of preservatives. The artificial

methods of seasoning and preserving timber are now diseased; thus if this statement is true it is a factor which must greatly influence the prospect of

receiving considerable attention as the price of wood

increases and the supply diminishes, so that this part recovery.

of the book should be of the greatest interest to all Dr. Schofield speaks in no uncertain manner con- concerned in the production and use of wood. cerning the tendency of some persons of the present In part iv. the felling and conversion of timber is day to mix up a “very exaggerated psycho-therapy adequately considered. The different instruments used

are also fully described and figured. In the last part with a pseudo-Christianity." We entirely agree with

is given an exhaustive account of almost every possible his remarks, and consider that he has stated the

means of timber carriage and transport. On the case none too strongly. In the chapter entitled “The whole, the author is to be congratulated on the proDiagnosis," we would specially commend to the duction of this excellent work. "udent the advice the writer gives of the “import- Illustrations of British Blood-sucking Flies. With ance of cultivating tact." There is probably no Notes by Ernest Edward Austen, Assistant, Departattribute of greater value to a physician, and no oppor- ment of Zoology, British Museum (N.H.). Pp. 74: tunity should be lost for developing it. The writer

34 plates. (Printed by Order of the Trustees, 1906.) very sound remarks concerning the personality of the “ doctor.” Some persons may

Gnats and other blood-sucking flies have always been consider that too much detail is given, and that some

a great pest in most countries, but it is only within

the last few years that their active agency in the advice is almost too trivial to be recorded; but with dissemination of many of the most serious diseases this view we should disagree, for undoubtedly the which afflict both men and the higher animals has strength of this book lies in the attention which is been fully recognised. In England, however, modern bontowed on detail.

drainage and sanitary regulations have far

diminished their numbers that whenever gnats are This book supplies a want, and certainly deserves exceptionally troublesome many people jump to the a place on the bookshelf of the young physician. conclusion that there has been an invasion of “mos

makes some

Price 235.

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quitoes (not knowing that the terms gnats and Bielschowsky for the staining of neurofibrils. Doubtmosquitoes are applied indiscriminately to any biting less these omissions will be rectified in a future species of Culicidæ), and, what is more important, edition. the gnats belonging to the genus Anopheles, though An excellent description is given of the microscopic far from extinct in England, have ceased to dis- characters of the various regions of the cerebral seminate ague as formerly.

cortex, the basal ganglia, the cerebellum, pons, Mr. Austen informs us that there are practically medulla, and spinal cord. The cranial nerves are disonly six families of blood-sucking flies in England, cussed with remarkable clearness, the diagrams illusChironomidæ (midges), Culicidæ (gnats or mosqui- trating this part of the book being particularly good. toes), Simulidæ, Tabanidæ (horse-flies), Muscidæ, and Finally, there is a concise account of the main Hippoboscidæ. In Chironomidæ and Muscidæ the sensory, motor, and association systems of fibres in habit is exceptional, occurring in a few species only, | the central nervous organ. The book is well indexed. and, except in the Muscidæ (and perhaps the Hippo- Dr. Villiger is to be congratulated on having proboscidæ), the habit is confined to the females. Mos- duced an excellent book. Not only does it amply quitoes, however, are also capable of subsisting on fulfil its avowed scope of serving as an introductory the juices of plants.

guide to the student, but it will be read with pleasure The illustrations in the present work are consider and profit by many neurologists. ably enlarged, and with few exceptions represent only Naturkonstanten in alphabetischer Anordnung. By females. The originals have been prepared for ex

Prof. Dr. H. Erdmann and Dr. P. Köthner. hibition in the north hall of the Natural History

Pp. 192. Museum. The letterpress consists of a brief general

(Berlin : Julius Springer, 1905.) Price

6 marks. account of each family, and a notice of the chief characteristics, habits, and localities of the various This handy little work is a book of constants intended species figured, technical descriptions, however, being for the use of chemists and physicists. It differs from omitted. Little has been done in England to others of its kind chiefly in the fact that the informpopularise the study of Diptera, and there are very ation in it is arranged alphabetically, with a marginal few illustrations of the species; so we welcome this thumb index for rapid reference. excellently arranged and illustrated book as a useful The work of the compilers has on the whole been contribution to our knowledge of the British Diptera. very well done. Only one value of each constant is

W. F. K. given, and usually no reference is made to the source

or author. The work of the last ten years has, howGehirn und Rückenmark. Leitfaden für das Studium ever, been incorporated to a much greater extent than

der Morphologie und des Faserverlaufs. By Dr. is usual in books of this kind, and even data only Emil Villiger. Pp. vii + 187; illustrated. (Leipzig : published during the past twelve months are included. W. Engelmann, 1905.) Price 9 marks.

The plan adopted by the compilers should conduce 10 There is no department of medical science in which a considerable saving of time in looking up informgreater advances have been made within the last ation. We think the book should be of especial value twenty-five years than in that of diseases of the to chemists, as the data necessary in quantitative central nervous system. This is mainly a result of analysis are dealt with in a specially complete manner. increasing precision in our knowledge of the compli- There are also tables giving for each element and its cated labyrinth of the various groups of nerve-cells most important compounds the atomic or molecular and nerve-fibres which compose the essential mech- weight, density, melting point, boiling point, thermoanism of the nervous system. The complexity of

chemical constants, &c., together with a five-figure the subject renders it a task of some difficulty to the logarithm table for computation purposes. Details as medical student, whether he be undergraduate or

to the most important spectroscopic features of each post-graduate, who is desirous of acquiring that

substance are given in a very handy form, the conthorough grasp of nervous anatomy on which the

ditions as to the particular spectrum being clearly successful solution of diagnostic problems must of specified. Another very useful table containing data

not often easily accessible is that of the electrochemical necessity depend. To such students as are able to read German can cordially recommend Dr.

equivalents of the metals. Villiger's book. Within the compass of 177 pages spend on a book of this kind to detect many of the

It is difficult in the time possible for a reviewer to the author discusses in lucid style the main facts of

errors nearly inevitable in a first edition. The plan the morphology of the brain and spinal cord, and

adopted by the writer has been to put the work for describes all the more important tracts of nerve-fibres.

a while on his reference shelf, and turn to it frequently An excellent series of illustrations, many of them

when looking up constants, verifying from other original, illuminate the text, whilst we are glad to

sources the data thus obtained. observe that the author evidently describes the gross

Obvious slips are the value of t, given on p. 114 anatomy as if demonstrating the actual brain, using ten times too small, the E.M.F. of the Clark cell. giren the diagrams as accessories. In this way the prac- , on p. 40 as 0.60735 volt, and several misprints among tical value of the book is undoubtedly enhanced.

the tables of English weights and measures, where Commencing with an account of the embryological the gallon is included under measures of surface. development of the nervous system, the author pro- Other inaccuracies are the value for the melting ceeds to discuss in detail the naked-eye anatomy of point of palladium, given as 1950° C. instead of the brain and spinal cord, with their surrounding 1525° C. † 25, of nickel, given as 1500° C. instead meinbranes. An interesting historical account is

of 1427° C., and of wrought iron, given as 1600° C. given of the successive stages in the methods of instead of 1500° C. neuro-histology, but we are surprised to find no One rather unfortunate tendency of the work is to reference to Marchi's well-known osmic acid method deal in a multiplicity of units. There is, for example, of staining recently-degenerated nerve-fibres, a method no need to speak of “hektowatts,” and it is certain which since its introduction more than ten years ago that some of the subdivisions of the millimetre dealt has done more than any other to clear up our know-with in the chapter on units are only confusing and ledge of nerve-tracts. Nor is any reference made to rarely met with in practical work. Then, also the the still more recent methods of Cajal and of units other than metric given in the book as at pre

we

was

recent

sent in use in various countries are not always those thermodynamic theory is quite independent of the particular ordinarily adopted. In Japan, for example, the pre- view we may adopt as to the fundamental nature of solu

Osmotic sent standard of mass is the “ Kwan,” prototypes of tion, and the modus operandi of osmotic pressure. which were recently standardised at Sèvres.

pressure may, as van 't Hoff himself supposed, be due to We can, however, cordially recommend the book, Armstrong believes, be caused by chemical affinity; it may

the impacts of the dissolved molecules; it may, as Prof. which should prove very useful.

J. A. H.

be produced by some other undiscovered cause. The thermodynamic reasoning avoids all such hypotheses, and

connects directly the experimental facts of the solubility LETTERS TO THE EDITOR.

of gases with the osmotic pressure they would exert [The Editor does not hold himself responsible for opinions

against a perfect semipermeable membrane in dilute solu

tion. expressed by his correspondents. Neither can he undertake

I have never suggested that the ultimate nature of soluto return, or to correspond with the writers of, rejected

tion was a matter of no interest. It is the question of manuscripts intended for this or any other part of NATURE. No notice is taken of anonymous communications.)

most supreme importance now outstanding in these subjects;

but let us clear the issue before attacking it. We must Thermodynamic Reasoning.

recognise clearly that the relations indicated by thermoIn the address delivered by Principal Griffiths at York,

dynamics and confirmed abundantly by experimentare

among the established facts to be explained by a theory of which is printed in your issue of August 9, I read : “ Prof. the nature of solution. Armstrong remarks that it is unfair to cloak the inquiry It is for this recognition of the true position of the by restricting it to thermodynamic reasoning, a favourite problem that I contend. The thermodynamic reasoning manæuvre with the mathematically minded.' He adds

which connects the ideal osmotic pressure with experithat such a course may satisfy the physicist but ‘is mental phenomena is not in question. That reasoning is repulsive to the chemist.'

The inquiry, "Why is the confirmed by measurements of actual osmotic pressures application of thermodynamic reasoning repulsive to the chemist? ' naturally suggests itself.”

and of freezing points. It can only be invalidated by a This statement shows a strange misapprehension of my

general attack on thermodynamic theory, such as that which

foreshadowed in Mr. Campbell's position. I have taken exception to the restriction of the reconnaisance-in-force. I do not think any such attack inquiry to thermodynamic reasoning, not in any way to has much chance of success. Osmotic phenomena seem the mere application of thermodynamic reasoning. My to me to be entrenched in the strongest part of the vast objection was to formula worship. I still and shall ever lines occupied by the science of thermodynamics. object to it, for it is the bane of progress. As I said at Cannot Prof. Armstrong agree to accept the thermoYork, physicists too nearly resemble the visitors to London dynamic reasoning as confirmed by experiment, and pass who walk along the Strand and Shaftesbury Avenue and are content to look at the theatres from outside ; they

on to the further problem? Personally, I think that the

evidence at present available is on the whole in favour resemble those who admire the British Museum building of the chemical theory of solution and osmotic pressure but have no desire to examine the treasures within it. --the theory which Prof. Armstrong supports; but there is

If I did not misunderstand him, Mr. Whetham implied work to be done before such a conclusion can be taken as at York that it was enough for him that a certain thermo- established. May we not agree that it is better both for dynamic expression was valid : what the condition termed

physicists and chemists to do such work than to waste osmotic pressure really is—whether a true pressure their energies in attacking with inadequate artillery the whether, as I suggested, a negative pressure or thirst- well-fortified citadel of thermodynamics? mattered not a jot. A certain mathematical thermodynamic

W. C. D. WHETHAM. picture being painted, no other artist need apply. This High Borrans, Westmorland, August 21. does not seem to me to be the attitude a scientific inquirer should adopt. Whether I represent the opinion of chemists

The Iron Arc. matters little : personally I am not willing to remain outside the Museum : I shall go inside, if possible, trusting

While carrying on some experiments with the electric that in some faint degree I may be able to appreciate the

arc between iron electrodes, one of my students, Mr. H. D. wonders within it.

Arnold, noticed that there was a certain critical P.D. at At present, progress is not a little hampered by the fact

which an abrupt change took place in the conditions of that chemists and physicists cannot wander through the

the arc. Subsequent investigation has shown that the effect museums of nature looking eye to eye in complete sym

of the carbon

is closely analogous to the * hissing point pathy with one another : surely we are destined to be the

How close the analogy is may be seen from the closest of friends ; more should be done to cultivate an

following remarks. If the iron arc is started with a large understanding; a confusion

external resistance and maintained at such a length that of tongues has arisen which keeps us apart : we must both strive to speak a simpler

the current is well below one ampere, it burns with little language. Together

or no sound, and its appearance in the neighbourhood of

the anode is very diffuse and ill-defined. As the external " let y« inspect the lyre and weigh the stress

resistance is gradually decreased, the P.D. falls and the Of every chord and see what may be gain'd By ear industrious and attention meet."

current rises until a certain critical value, depending on Henry E. ARMSTRONG.

the length of arc and size of electrodes, is reached. At this point a very small decrease in external resistance

suffices to cause a sudden increase in current and drop in It is the strength and weakness of thermodynamical P.D., precisely as with the carbon arc. At the same time reasoning that it connects different phenomena without the the arc contracts, a bright spot appears on the anode, and aid of theories about the mechanism by which the connec- a characteristic hissing sound begins. Further increase of tion is effected.

current is accompanied by a continued decrease in P.D. In the discussion at York, Prof. Armstrong put forward The hissing stage, in fact, begins at quite a different poi Certain arguments in favour of the view that solution is a on the P.D.-current diagram from that in the case of the chemical phenomenon, and osmotic pressure due to carbon arc. If the experiment is carried out in the reverse attraction of the nature of chemical affinity. He used these order, starting with a large current, the discontinuity is arguments in an attempt to invalidate van 't Hoff's encountered again, but not until the current has been thermodynamic theory, which shows that, from the observed diminished beyond the value that it had at the beginning solubility phenomena of volatile substances, it follows that of the hissing stage. Indeed, with arcs of 6 mm. and the ideal osmotic pressure of a number of particlns of more, the current on the hissing stage can with care be such substances in a dilute solution must be equivalent decreased until it is smaller than its previous largest value to the pressure which the same number of particles would on the quiet stage. Thus there are two possible values exame as a gas occupying the same space.

of P.D. for the same current and length of are, In my reply to Prof. Armstrong 1 pointed out that the corresponding to the quiet, the other to the hissing stage.

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Stapediatel'soafetimenebef nothiese i abrupte changes ethen quiet In the year 1775. Priestley published kinds of modern

How closely the physical cause of this discontinuity usually accepted that

" radiation always accompanies resembles that in the case of a carbon arc is still in doubt, the projection of “Bparticles, and the extreme penetrathough investigations bearing on this question are under tion of the " 2 rays seems to be directly due to the very way. With the iron arc there seems to be no sharply high velocity of the average Bparticle. As the defined crater, for each electrode terminates in a viscous, efficiency of the “ X rays is due to the sudden negative incandescent globule of what seems to be magnetic oxide acceleration of the unit electrical charges (i.e. the corof iron, from which the discharge takes place. Thus we puscles) as they strike the anti-kathode, it appears quite have to do, properly speaking, not with an arc between possible that corpuscles, moving with comparatively lou iron electrodes, but with one between electrodes of Feo, velocities, may yet be capable of causing a form of “, Even when the arc is hissing strongly, the discharge seems radiation of feeble penetrating power. The fact that the to take place from only a small area on the surface of kathode stream, which can hardly penetrate the glass oi the globule. Moreover, a large increase in diameter of the tube, is still able to set up very penetrating X radiation electrodes is accompanied by only a small increase in the when given a sudden negative acceleration by impact with value of the critical current, which varies between 0.8 the platinum anti-kathode may perhaps be given as an ampere and 1.5 ampere over a wide range of values of instance in support of this idea. It seems probable that the length of arc and thickness of electrodes. On the other photographic action of a beam of corpuscles (deviated away hand, I have found no positive evidence that the discon- from the g" radiation by a magnetic field) may be tinuity is not due to the presence of oxygen around the chiefly due to a form of " g ray set up on contact with anode. A test with an exploring electrode showed that the plate itself. The several mysterious instances of the the effect is confined mainly, if not entirely, to the anode. fogging of photographic plates left in certain conditions Given an are burning on the quiet stage in the neighbour- for considerable periods may be caused by a very feeble hood of the hissing point, the hissing can be precipitated form of “q” radiation set up by the impact of slowby shortening the arc, just as in the case of the carbon moving corpuscles on the surrounding matter. Such

evidence of these slow-moving corpuscles may be somewhat After the current has been increased somewhat beyond meagre and doubtful, but I think that, so far as the the hissing point, the arc begins to rotate rapidly, so that ordinary chemical elements are concerned, the emission of on the anode a ring instead of a spot of light appears.

such corpuscles may be very much greater than the This is accompanied by a high-pitched squeak or whistle,

measured activities would lead us to suppose. which, as the current is still further increased, degenerates

C. W. RAFFETY. into a sputter, and this in turn into a steady, strong hiss,

Streatham Common, August 25. the ring meanwhile having disappeared. At the beginning of the **

whistling stage the arc has a curious tendency to jump back into the quiet stage, so that for an instant the hissing ceases, the current falls abruptly, and the P.D.

THE OXIDATION OF ATMOSPHERIC NITRO. rises several volts. If one begins to diminish the current

GEN IN THE ELECTRIC ARC.

N maintained steadily, though ments Observations on Various Air," the current is far greater than that at which hissing in which he showed that when a series of sparks was normally occurs. It is not impossible that slight irregu- passed through air, the air became acid. The experilarities in the supply E.M.F. may in certain circumstances serve to precipitate the change from the one stage to the

ment was carried out by means of a glass tube, having other, even though the current be not that at which the

one end closed with wax through which a wire was change normally takes place.

fixed, the open end being placed over a solution of In conclusion, the question may be raised whether blue litmus. Sparks were passed between the solution Lecher's observation of the discontinuous nature of the

and the wire, and in a short time the blue litmus are discharge between iron electrodes was not made on turned red. He further noticed the important face the hissing stage alone, and whether, as with the carbon that the water gradually rose up towards the wire. arc, the discharge may not be perfectly continuous when The observations of Priestley were shortly afterwards the current is made sufficiently small. It is planned to substantiated by Cavendish, and in 1893 Lord Rai. repeat Lecher's experiment, making tests both the leigh, with better apparatus and appliances, repeated quiet and the hissing stages of the iron arc.

the experiments which ultimately led him to the Middletown, Conn., August 9.

W. G. Cady.

discovery of argon. Priestley attributed the acidity

to the formation of carbon dioxide, but Cavendish, on Volcanoes and Radio-activity.

repeating the work, proved it to be due to the forma

tion of nitric and nitrous acids. In the Popular Science Monthly for June Major Dutton has an interesting article on the above subject, which was

After the successful experimental work of Lord Rarnoticed in a recent issue of Nature. Having been occupied leigh, attention was turned towards the production of lately with the study of volcanoes in connection with a

nitric acid from atmospheric nitrogen. But it was more general inquiry into the cause of earthquakes, it undoubtedly due to Sir William Crookes, who as occurs to me to point out that Major Dutton has over

president of the British Association in 1898 directed looked the recognised distribution of volcanoes about the attention to the gradual depletion of the world's store sea coast, which seems completely to invalidate his theory. of nitrogenous products, that the importance of the If radium, which the researches of the Hon. R. J. Strutt fixation of atmospheric nitrogen was recognised by have shown to be so abundant in typical rocks of the the scientific and commercial world. At the present earth's crust, such as granite, were an exciting cause of time about 15 million tons of Chili saltpetre are volcanic activity, we should expect to find an abundance annually exported, but those who have studied the of active volcanoes in the interior of continents, such as the l'nited States, Europe, Asia, Africa, Australia, and

question consider that at this rate of exportation the Brazil, which is contrary to observation.

Chilian beds will be, at the latest, depleted by 1940.

But as the population of the world increases, th

T. J. J. See. Naval Observatory, Mare Island, California, August 10.

quantity of nitrogenous material required for fertilising purposes advances in equal ratio. Sir Willian

Crookes pointed out in 1898 that the world's growth The Radio-activity of the Chemical Elements. of wheat was about 163,000,000 acres, which at the IN connection with the emission, from the radio-active average of 12.7 bushels per acre gave 2,070,000.00 plements, of corpuscles with velocities below the critical bushels. “But thirty years hence the demand wil velocity necessary for the ionisation of gases, it has occurred be 3,260,000,000 bushels. . . By increasing the to me that such a form of radiation is possibly a fairly present yield per acre to twenty bushels, we should general property of the chemical elements. It is, I think,

with our present acreage secure a crop of the requins

on

3

amount." In order to give this increase, about 1.5 which are water-cooled, and are in the form of a cwt. of nitrate of soda would be required to be applied narrow, elongated U; even with flames of 750 kiloannually to each acre, that is to say, 12,000,000 tons watts at 5000 volts the same form of electrode can be would be needed. As at present situated the world employed. By cooling the electrodes, about 7-5 per is not in a position to supply this vast amount of nitrogenous product. Since Crookes sounded this note of warning many attempts have been made to oxidise atmospheric nitrogen on a commercial scale, but until within the last fifteen months no process based upon electrical oxidation has been an actual commercial success. It yet remains to see whether the process of Drs. Caro and Frank, which depends upon the formation of calcium cyanamide, will be able to compete in the first place with natural nitrates and ammoniacal products, and, secondly, with the electric process of Birkeland and Eyde, which, as we will shortly show, appears to have solved the problem of the fixation of atmospheric nitrogen. Drs. Caro and Frank found that by passing nitrogen over heated barium carbide barium cyanide was produced thus,

BaC, +N, =Ba(CN),
but that when calcium carbide was employed' calcium
cyanamide and not calcium cyanide is formed,

CaC, + N,=CaCN,+C.
When the cyanamide is heated with water under

Fig. 1.- View of nitric acid factory at Notodden.
pressure it is decomposed with formation of ammonia
and calcium carbonate,

cent. of the electric energy employed between the

electrodes is removed as heat by the water. CaCN,+ 3H,O=CaCO, +2NH,.

Prof. Birkeland explains the formation of the discThis process is stated to take place slowly when the flames in the following way :-" At the terminals of the cyanamide is distributed on the soil. Although the closely adjacent electrodes, a short arc is formed, estamanufacturers state that cyanamide is stable and does blishing an easily movable and ductile current connot deteriorate on keeping, some at least of the users ductor in a strong and extensive magnetic field, i.e. say it is unstable and deteriorates considerably as a

from 4000 to 5000 lines of force per sq. cm. in the fertiliser when kept.

centre. The arc then moves in a direction perpendiAn electrical process—that of Bradley and Lovejoy cular to the lines of force, at first with an enormous --which was almost a success, was worked for about velocity which subsequently diminishes; and the exeighteen months at Niagara. They employed a con- tremities of the arc retire from the terminals of the tinuous current with a potential of 10,000 volts. As electrodes. As the length of the arc increases, its it is very difficult to keep steady discharges at this electrical resistance also increases, so that the tension high voltage, a slowly rotating framework with pro- is increased until it becomes sufficient to create a new jecting electrodes was employed. As it rotated, the are at the points of the electrodes. The resistance of electrodes, which were of platinum, approached other this short arc is very small, the tension of the elecprojecting electrodes; discharges were thus provoked, trodes therefore sinks suddenly, with the consequence but immediately interrupted. In an apparatus of only that the outer long arc is extinguished. ... In an 5 kilowatts as many as 414,000 arcs were produced per

S. minute. The working of such an apparatus on a technical scale was, as might be supposed, of great difficulty, and although considerable quantities of nitric acid were produced per kilowatt year, it did not prove commercially successful.

In May, 1905, a factory was started at Notodden, in Norway, for the manufacture of calcium nitrate from air and limestone by means of the electric arc flames. A photograph of the factory as it is at present is shown in Fig. 1. In the Birkeland-Eyde process, which is worked at Notodden, a high-tension arc flame is produced between two pointed copper electrodes. The electrodes are attached to a high-tension alternator, and are placed equatorially between the poles of a powerful electromagnet, so that the terminals of the electrodes are in the middle of the magnetic field. An electric disc flame is thus produced which is shown diagrammatically in Fig. 2, and a photograph of the actual flame in Fig. 3. The photographed flame.

Fig. 2.- Diagram of electric arc fame. which represented about 250 h.p., was produced between water-cooled electrodes made of copper alternating current all the arcs with a positive directubing.

tion of current run one way, while all with a negative The working potential employed is 5000 volts, the direction run the opposite way (see Fig. 2), presupposcurrent is an alternating one of 50 periods per second, ing the magnetising being effected by direct currents. and the distance of the terminals apart is about 8 mm. In this manner a complete luminous circular disc is As already mentioned, the electrodes are copper tubes presented to the eye.”

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