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THE CHEMICAL NEWS.

VOL. XXXIX. No. 1004.

ABSORPTION OF GASES BY CHARCOAL.

PART II.

ON A NEW SERIES OF EQUIVALENTS OR MOLECULES.* By R. ANGUS SMITH, Ph.D., F.R.S.

IN the Transactions of the British Association, 1878, Norwich, on page 64 of the Abstracts, there is a preliminary notice of an investigation into the amount of certain gases absorbed by charcoal. I made the inquiry from a belief previously expressed in a paper of which an abstract is in the Proceedings of the Royal Society, page 425, for 1863. I said in that paper that the action of the gas and charcoal was on the border line between physics and chemistry, and that chemical phenomena were an extension of the physical; also that the gases were absorbed by charcoal in whole volumes, the exceptions in the numbers being supposed to be mistakes. The results given were :

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It was remarked that the number for nitrogen was probably too low; I had some belief that the charcoal retained a certain amount which I had not been able to estimate.

For common air, the number 40.065 crept into the paper or abstract instead of the quotient 7:06

I considered the numbers very remarkable, but was afraid that they would be of little interest unless they could be brought more easily under the eyes of others; my experiments were somewhat laborious; the exact numbers were seldom approached by the single analysis, but were wholly the result of a series of irregular averages and apparently irregular experiments. The cause of this was clear, as I believed, namely, the irregular character of the charcoal with which I had to deal. The experiments were forgotten, I suppose, by most men, but the late Prof. Graham told me that he had repeated them with the same results that I had published. I might have considered this sufficient, but waited for time to make a still more elaborate investigation of the subject, and to take special care with oxygen, in the belief that, the rule being found, the rest of the inquiry would be easy; this was extended to nitrogen, but not by so many experiments as with oxygen. I am now assured of a sound foundation for inquiries, which must take their beginning from the results here given.

It is found that charcoal absorbs gases in definite volumes, the physical action resembling the chemical.

Calling the volume of hydrogen absorbed 1, the volume of oxygen absorbed is 8. That is, whilst hydrogen unites with eight times its weight of oxygen to constitute water, charcoal absorbs eight times more oxygen by volume than it absorbs hydrogen. No relation by volume has been hitherto found the same as the relation by weight.

The specific gravity of oxygen being 16 times greater than hydrogen, charcoal absorbs 8 times 16, or 128 times more oxygen by weight than it does hydrogen. This is equal to the specific gravity of oxygen squared and 2. Abstract of a Paper read before the Royal Society Feb, 6, 1878.

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These four results belong to the early group not cor" roborated lately, but so remarkably carrying out the principle of volume in this union, giving numbers the same as those of weight in chemical union, that they scarcely require to be delayed.

I am not willing to theorise much on the results; it is here sufficient to make a good beginning. We appear to have the formation of a new series of molecules made by squaring our present chemical atoms, and by certain other divisions peculiar to the gases themselves. Or it may be that the larger molecule exists in the free gas, and chemical combination breaks it up. These new and larger molecules may lead us to the understanding of chemical combinations in organic chemistry and whenever there is union not very firm, and may also modify some of our opinions on atomic weights and the motion of gases.

Of course, I cannot pretend to give the result of these results; but as we have here the building up of a molecule by volumes, so as to form an equivalent of physical combination analogous to the chemical equivalent, it is impossible to avoid seeing that it indicates the possibility of our present equivalents being made up in a similar

manner.

I did not expect these numbers; but I certainly, as my previous paper showed, had in full view a necessity for some connexion between physical and chemical phenomena more decided than we possessed.

VOLUMETRIC ESTIMATION OF SUGAR BY AN
AMMONIATED CUPRIC TEST GIVING
REDUCTION WITHOUT PRECIPITATION.*
y F. W. PAVY, M.D., F.R.S.

TO BE able to effect the quantitative determination of a body with accuracy and facility is an important matter looked at in relation to the study of its bearings. In the case of sugar there are no reliable means of precipitating and weighing it, either alone or in combination, and thus in the chemical estimation of this principle an indirect method has to be resorted to. The only property upon which dependence car. be placed, for the purpose of chemical quantitative analysis, is its reducing action, under the influence of heat, upon certain metallic oxides, and that of copper is the one which general experience shows to answer best.

In the ordinary volumetric application of the copper

* A Paper read at the Royal Society, January 16, 1879

78

Volumetric Estimation of Sugar.

CHMMICAL NEWS, February, 21, 1879.

test the precipitation and diffusion of the reduced sub- | with a sufficiency of sugar to effect the complete reducoxide through the liquid interferes with the clear perception of the cupric oxide present to the state of suboxide. tion of the precise point of complete decolouration, and As the saccharine product is dropped in the blue colour thus detracts from its delicacy. For purposes where gradually fades, without any occurrence of precipitation to minute accuracy is of no moment, a sufficiently approxi- interfere with the perception of the precise moment when mate result can be obtained, but for physiological investi- the point of complete decoloration is attained. The amgation, and in other cases where precision is indispensa- monia exerts no interference with the process of reducble, the process is quite unfit for employment. tion, but simply dissolves the reduced oxide, leading, when complete decoloration is effected, to the production of a perfectly colourless, limpid liquid.

With the view of obtaining increased accuracy, chemists have had recourse to the plan of collecting the precipitate of reduced suboxide and weighing it as such or after reconversion into the oxide. From the difficulty, however, that exists in procuring the metallic oxide in a pure and uniform state, and from the impossibility of completely freeing the filter paper used from adhering surplus copper solution, some uncertainty is given to the results obtained by this method. To obviate the difficulty here presented I suggested, in a communication published in the Proc. Roy. Soc. for June, 1877, that the precipitated suboxide should be collected and dissolved, and the copper frequently thrown down by the agency of galvanic action upon a platinum cylinder, as is now frequently done in the assaying of copper ores. The process has been found, as shown by the closeness observable in the results of counterpart analyses, to admit of the greatest precision, and I have turned it to extensive account in some recent physiological investigations I have conducted. In its application to such a purpose it may be held that time and labour should be considered as of no moment, but it frequently happens that a more ready process of investigation is needed than the gravimetric supplies, and on this account a volumetric method, free from the objection I have pointed out as belonging to the ordinary plan, constitutes a desideratum.

matter.

A few years back Bernard introduced, for physiological purposes, a modification of the ordinary volumetric process, which is attended with reduction and the non-precipitation of the reduced oxide. The process involves the employment of a large quantity of caustic potash, and the presence in the product to be tested of extraneous organic Under these circumstances it happens that the reduced suboxide is held in solution instead of being allowed to fall, and thus decoloration without precipitation occurs and enables the point of disappearance of the colour of the test to be ascertained with precision. Bernard, in his remarks upon the test, simply made mention of the fact that under these conditions reduction without precipitation took place, but Dr. d'Arsonval, his Prépa rateur at the College of France, refers the effect to the solvent influence of the extraneous organic matter in presence of the alkali.

Whilst engaged upon an enquiry into the merits of this test, the conclusion suggested itself to me that the agency preventing the deposition of the suboxide was the development of ammonia. With an absolutely pure solution of sugar, such as may be obtained by inverting the ordinary crystallised cane sugar (refined loaf sugar) no amount of potash will hinder the instantaneous precipitation of the suboxide. With commercial grape sugar, however, and in a still more marked manner with honey, interference with precipitation is exerted, and this, I am led to conclude, is due to the action of the potash in producing ammonia from the small quantity of nitrogenous organic matter incidentally present.

With this before me, the idea presented itself of resorting to the direct employment of ammonia for attaining the same result. It is well known to chemists that ammonia is a powerful solvent of the suboxide of copper, leading to the production of a perfectly colourless liquid; and this, from the facility with which it absorbs oxygen, quickly assumes a blue colour under exposure to air from the re-conversion of the cuprous into the cupric oxide.

If ammonia be added to the ordinary Fehling's solution, a liquid is obtained which is rendered colourless by boiling Gazette Hebdomadaire de Médicine et de Chirurgie, September

14, 1877, p. 454.

Enough ammonia must be present to secure that the suboxide is held in solution, and precaution must be taken that whilst the analysis is being performed the reduced oxide does not become re-converted into the oxide by exposure to the air. To obviate this the operation should be conducted in a flask instead of an open capsule. The appliance that naturally suggests itself as most suitable for employment is a flask of about So cub. centims. capacity, with a cork inserted into the neck, through which a delivery tube from a Mohr's burette, graduated in tenths of a cub. centim., passes for dropping in the product to be examined. Through the cork, also, there must be an exit tube for the escape of air and steam from the flask. Should it be desired to avoid the impregnation of the surrounding atmosphere with ammonia, the exit tube may be connected by vulcanised tubing with a U-shaped tube containing fragments of pumice stone moistened with water or a wead acid. The burette being fixed in the stand, the flask is allowed to hang suspended, so that there may be nothing to obstruct the full view of the contents. The heat is applied by means of the flame of a spirit-lamp, and the best position for watching the disappearance of colour is by the light reflected from a white background specially provided for the purpose. It is con. venient to have another burette, graduated in cub. centims., and of 100 cub. centims. capacity, fixed in the stand for holding and delivering the ammoniated copper solution. Messrs. Griffin, of Garrick Street, have constructed an arrangement to meet the requirements.

I at first took it for granted that in the action occurring the same relation existed between the amount of oxide of copper reduced and that of sugar oxidised, as under the employment of the copper test in the ordinary way, viz., that 5 atoms of oxide of copper were reduced by i atom of sugar, and the liquid I first employed was prepared by adding to 100 cub. centims. of Fehling's solution 300 cub. centims. of strong solutions of ammonia (sp. gr. o 880) and 600 cub. centims. of distilled water. The liquid thus made contained one-tenth of Fehling's solution, and if it comported itself in the same manner as the latter, 1o cub. centims. of it would stand equivalent to o'005 grm. of grape sugar. In working with this liquid the results obtained were so accordant in relation to each other that I had no misgiving about its uniformity of action; but I felt that before being definitely accepted they ought to be checked against known amounts of sugar. The accomplishment of this proceeding, however, is not altogether unattended with difficulty, on account of the uncertainty of obtaining grape sugar free from impurity and in a perfectly dried state.

The method I have adopted has been to operate upon weighed amounts of cane sugar and produce inversion by boiling with an acid. I first found that the cane sugar, which is sold in coarse colourless crystals-that which is known as "white crystal," and used for sweetening coffee

stood the test on examination for purity with Laurent's polarimeter. A weighed quantity was taken, and, after being inverted by boiling with hydrochloric acid, the acid neutralised, and the liquid brought to a known volume, subjected to treatment with the ammoniated copper liquid. Repeated trials were made with varying quantities, and it was found that the results stood in harmonious relation to each other, but that the amount of sugar indicated was larger than the calculated amount of invert sugar from the weighed quantity of cane sugar taken. At first I was at a loss for an explanation of this result, but subsequent

observation has revealed that in the case of the ammo- | deposition of a certain amount of suboxide. Not so, howniated liquid, 6 atoms of oxide of copper are appropriated ever, with the ammoniated liquid. Here the conditions by I atom of sugar, instead of 5, as in that of Fehling's solution used in the ordinary way. When the reckoning is made upon this basis the results exactly correspond with the actual amount of sugar known to be present. Moreover, with solutions of ordinary grape sugar and diabetic sugar, examined comparatively with Fehling's solution used in the ordinary way and the ammoniated copper liquid, the results exactly accord under the reckoning that 5 atoms of oxide of copper are appropriated in the one case and 6 atoms in the other by 1 atom of sugar.

To be quite satisfied upon this point, a large number of observations under varying conditions have been made, and whilst what I have stated holds good for the ammoniated copper liquid prepared from Fehling's solution, without any further addition of alkali, and with the addition of potash to the extent of 1 grm. to 20 cub. centims. of the ammoniated test, yet a larger quantity of potash alters the action, and with 5 grms., and anything beyond, the behaviour is brought to the same as that of Fehling's solution used in the ordinary way, viz., 5 atoms only of oxide of copper are appropriated by 1 atom of sugar. With quantities of potash between the I and 5 grms., the results stand between the 5 and 6 atoms of cupric oxide. I may mention that observation has further shown that whilst glucose prepared from starch behaves like other varieties of grape sugar, there is an intermediate product formed before the completion of the process of conversion, which behaves in a different manner from invert sugar, grape sugar, and sugar of diabetes. Estimations made with the ammoniated copper liquid coincide with those made with Fehling's solution without the presence of ammonia, and the addition of potash to the ammoniated liquid produces no modification of the result.

In order that the ammoniated copper liquid may be brought to the same standard of sugar value as Fehling's solution, and it is desirable that this should be the case, the proportion of copper must be increased so as to give 6 atoms against 5. By taking 120 cub. centims. of Fehling's solution, 300 cub. centims. of strong ammonia (sp. gr. 0.880) and making up to a litre with distilled water, the proper proportion is obtained, and the ammoniated liquid gives results corroborated in accuracy by the balance, and coinciding with those obtained by Fehling's solution employed in the ordinary way.

As a minor point it may be remarked that the diluted state presented by the ammoniated liquid offers an advantage by diminishing the liability to error arising from any want of absolute precision in measurement.

are such that under exposure to air the copper cannot fail to remain in solution and to be maintained in a fully oxidised state. A further advantage is given by the influence of the presence of ammonia on the colour of the test, for, in proportion to the height of colour of a volumetric liquid, so is its degree of delicacy as a reagent, and the effect of the addition of ammonia to the ordinary copper test is to considerably increase the blue colour belonging to it.

Seeing that the test here proposed acts with equal efficiency either in the presence or absence of extraneous organic matter, it is alike adapted for employment by the chemist, the physiologist, and the medical practitioner in

relation to diabetes.

THE PREPARATION OF SINGLE REGULAR CRYSTALS OF ANY DESIRED SIZE.*

MR. FERDINAND MEYER, who has for thirty years studied the conditions necessary for obtaining large, single, and regular crystals of chemical salts, has published his method in the Archiv der Pharmacie, October, 1878, from which we take the following:

Prepare a solution of any salt in water of such a strength that, after standing twenty-four hours, a portion of the salt will separate in crystals. Pour off the motherwater, select a few of the best formed crystals, and place them on a plate of glass, which lies in a rather tall vessel. Then re-dissolve a little of the dry salt in a small quantity of the mother-water, add this supersaturated solution to the main bulk of the mother-water, pour this upon the crystals on the plate of the glass, and place the vessel into a room where the temperature remains as uniform as possible, best in the cellar. The temperature of the room should be ascertained by a thermometer, and in case of any changes of temperature, a further quantity of the sait is to be dissolved in the mother-water. This must be repeated every twelve or fourteen hours, until the crystals have reached the desired size. If the solution is too strong, single regular crystals are seldom obtained at once, but this is generally of no consequence, for, as long as one side at least is perfectly formed, it is only neces sary to turn them two or three times to cause the other sides likewise to become perfect. As the crystals increase in size care must be taken to give them a correct position in the plate of glass: and, if the solution is at all concentrated, the crystals must be carefully freed from adhering irregularities, and then replaced in the solution. In a solution of alum, a very oblique octoëder is usually obtained first. This may be allowed to reach a considerable size, after which it is to be laid successively on the narrow sides, when it will gradually become a regular octoëder. If it is always kept lying on the broadest sides it will continue to grow obliquely.

Twenty cub. centims. of the ammoniated copper solution, corresponding with o'oro grm. sugar, having been run in from the burette containing the test, the flask is adapted to the cork attached to the delivery tube of the other burette containing the saccharine product for examination. The flame of a spirit-lamp is then applied underneath, and the contents of the flask brought to a state of ebullition and allowed to boil for a few minutes in order to get rid of the presence of air. The saccharine product It is well known that several isomorphous salts may be is now allowed to drop from the burette until the blue crystallised, one over the other, in layers, without a colour of the test is just removed, and a perfectly colour-change of crystalline form. Chrome-alum crystals may less limpid state produced. thus be covered with crystals of ordinary alum.

On account of the ammoniated copper solution used tion, it is necessary that the product to be examined should not be in too concentrated a form. For delicate

being only equivalent to 2 cub. centims. of Fehling's solu

observation it is convenient that the dilution should be such as to require the employment of from about 10 to 20 cub. centims. to decolourise the 20 cub. centims. of the ammoniated copper solution.

The ammoniated copper solution enjoys the advantage o possessing a self-preservative power. It is well known in the case of Fehling's solution that, in the course of time, not only does the liquid become impaired in stability, but actually reduced in strength, by the spontaneous

The

largest crystal of this kind obtained by the author weighed

over three pounds.

The author also observed that, when employing the same mother-water for a considerable time, the crystals began to show blunt or flattened points. This happened with regular as well as with oblique crystals, so that in place of eight surfaces, the regular crystals gradually assumed sixteen equal sides, and the irregular ones, fourteen smaller and two larger sides. If, however, the mother-water be acidulated with a little sulphuric acid, this flattening of the point occurs but rarely.

F:om "New Remedies," January, 1879.

80

Analysis of Bleaching-Powder.

As a general rule, this changing the position of the single crystals of any salt, but particularly of sulphate of zinc, copper, nickel, or magnesium, and of Rochelle salts, different forms of the same system are obtained. If crystals of Rochelle salt, which may easily be obtained of large size, are always placed upon one and the same side, one-half of the crystal will become perfectly developed; but if they are laid, alternately, upon the two opposite long surfaces, the development is less regular. On placing large crystals of the same salt, even if only half developed, lengthwise into the liquid, alternately upon either end, development of the lateral surfaces proceeds very regularly.

It is not advisable to introduce crystals into a solution if the latter is at all warm, or to pour a warm solution into a cold one containing crystals, as the latter are thereby generally torn or broken. If a portion of a crystal has been by accident broken off, it may be repaired by subjecting it to the above-detailed process. In a crystal of chrome alum, from which a piece weighing ten grms. had been broken off, the gap was completely restored by subjecting it to the feeding process for a fortnight.

As soon as the crystals have attained the desired size it is best to place them into less concentrated solutions, in a slightly cooler place; this after-treatment causes the surfaces to become smooth and levelled, and the edges to become sharp.-Pharmaceutical Journal.

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CHEMICAL NEWS, February 21, 1879.

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In the first table are the analyses of six pure flours. I was satisfied that they were quite free from alum, and yet I found alumina equal in No. 1 equal to 24°30 grs. of alum per 4 lbs.

The first four flours came from a large mill where much foreign grain is used, and No. 6 was made at a small country mill from English grown wheat alone. It occurred to me that the quantity of alumina in flour might depend on the variety of grain from which it was prepared; and with a view to ascertain if such were the case, I made several analyses of wheats from different countries, and have tabulated the results.

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No.

I.

Variety of Wheat. Calcutta

2.

Ditto

3.

Ditto

18.50 20'00 170'00

4.

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5.

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6.

Russian

7.

Ditto

8.

Ditto

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In 24 hours it absorbed 25 per cent of moisture.

9.

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A small quantity now left is in a liquid condition.

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The sample was sold as containing 35 per cent of available chlorine, but was found to only contain 28.6 per

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THE quantity of alumina naturally present in pure flour and bread has been a subject of discussion for many years, and has been erroneously assumed by some chemists not to exceed an amount equal to 8 or 10 grains of alum per 4 lbs. At a meeting of the Society of Public Analysts, February 5, 1875, it was stated by one speaker to be as low as 2 grs., and by others as high as 10 grs., expressed as alum per 4 lbs. of bread; and a rather prominent analyst asserted at the "Selby case" a few months ago that, in his opinion, 2 grs. were quite sufficient to allow for. It has recently

Nos. 1, 2, 3 are Calcutta wheats, now largely imported and much prized by millers. The following six refer to Russian wheat. The Kourish variety is particularly high in alumina and silica. Nos. 10 and 11, and the English wheats, Nos. 12 to 15, are very much alike. No. 18 was a sample of Californian wheat, a pretty looking, large, white grain, remarkably low in alumina and iron oxide. No. 19 was a mixture of II varieties mixed by a miller preparatory to grinding. Egyptian wheat, as imported, is much intermixed with clay. It seems that the lighters in which it is carried on the Nile are unprovided with hatches, and in lieu of them the cargo is covered with mud, which is soon baked hard in the sun and gives a firm footing to the boatmen. This rough treatment accounts, no doubt, for its presence in the form of dust, pellets, and lumps. It is always more or less cleansed preparatory to grinding; but it does not appear practicable, with the cleansing apparatus attached to the best constructed mills, to get rid of all the extraneous matter in

grain. Sometimes the holes made by the weevil (an in- | boiled for about half an hour. I found that by this process, sect infesting some kinds of wheat, Calcutta for instance) are filled with dirt, and no amount of working or screening will extract it.

A glance at the table will show what kind of flour to expect from any of the wheats. It is rarely, however, that any one kind is ground by itself. It is the practice of millers to mix several kinds, and the mixture varies in every mill and in every part of the county according to the supply of foreign grain and the quality of our homegrown.

No. II. Table shows that some varieties of wheat are more contaminated than others with alumina. I use the word contaminated advisedly, as I believe that the greater portion of it is due to extraneous matter, and it reveals the source of the excessive quantity of alumina occasionally met with in flour.

Since it is impossible to fix upon a standard of natural alumina, and since it is erroneous to regard its amount, even in the presence of alum, as in any degree a measure of alum, it may be asked-What is the use of estimating it at all?

I venture to suggest that it might indicate whether the grain was or was not cleansed properly before grinding; but the estimation of silica would answer just as well. Experience will enable us, perhaps, to decide on the limit to allow for clay in flour. If a line were drawn somewhere it would probably make millers more careful in the cleansing process.

It

Dr. Dupré's "chloroform " method of separating alum from flour appears from his reports to be satisfactory. A correct quantitative test for alum in bread is still a desideratum. As for a qualitative test, there cannot be anything more simple and certain than the logwood test properly applied. I have tried it repeatedly with different kinds of flour and bread, and never found it to fail. does not matter, in my opinion, whether the solution is new or old, and all the logwood chips I have come across answer well. I have never found any difficulty in distinguishing the alum colour from that caused by soil, magnesia, or any probable constituents of flour or bread. I therefore place implicit trust in it, and feel rather surprised that its efficiency is sometimes questioned.

Hull, January 31, 1879.

it is easy to destroy all matter, except the oxide, capable of liberating iodine on treatment with potassic iodide and hydrochloric acid. The solution having been cooled, it was mixed with excese of potassic iodide, and then with enough hydrochloric acid to dissolve the suspended oxide. The liberated iodine was then estimated by a standard solutiou of sodic thiosulphate (Na2S2O3).

In the first experiments I used a standard solution of nitrate of nickel, and calculated the nickel from the iodine set free according to the following equation:--Ni2O3+6HCl=2NiCl2+Cl2+3H2O.

The results were not satisfactory, as will be seen from the following Table:

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WHILE preparing standard solutions of nickel and cobalt salts for the purposes of a research on the colorimetric relations and on the colorimetric estimation of those metals, I was endeavouring to use a modification of the method of estimating nickel and cobalt, indicated by Bunsent, depending for their determination on the iodine liberated by the higher oxides of these metals in contact with hydrochloric acid and potassium iodide. The method was as follows:-The solution of the nickel or cobalt salts was made alkaline by soda and then mixed with excess of sodic hypochlorite obtain by the action of cold dilute sodic carbonate on fresh bleaching-powder.

After allowing the slightly warm solution of nickel or cobalt to stand some time, so as to ensure complete oxidation, the temperature was raised until brisk effervesence ensued, and the solution allowed to remain at that temperature until the excess of hypochlorite was decomposed. When the evolution of oxygen had ceased, the liquid was

A Paper read before the Royal Irish Academy, June 25, 1877. + Ann. Ch. Pharm., lxxxvi., 265.

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