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212 Deviation of Polarised Light by Solutions of Inverted Sugar.

tainty of gun-cotton in the earlier stages of history, naturally gave rise to a persistent scepticism regarding its presenting trustworthiness, appears now also about to adopt wet gun-cutton for military and naval uses.

But while the usefulness and great value of compressed gun-cotton in these important directions has been established, its technical application has made but slow progress as compared with that of the simple nitroglycerin preparation known as dynamite, which, in point of cost of production and convenience for general blasting purposes, can claim superiority over compressed guncotton. Already, in 1867, a number of dynamite factories, working under Nobel's supervision, existed in different countries; in that year the total quantity manufactured amounted to 11 tons; in another year the produce had -risen to 78 tons; in 1872 it had attained to 1350 tons. Two years afterwards the total production of dynamite was nearly trebled, and in 1878 it amounted to 6140 tons. There are as many as fifteen factories in different parts of the world (including a very extensive one in Scotland) working under the supervision of Mr. Nobel, the originator of the nitro-glycerin industry, and some six or seven other establishments exist where dynamite or preparations of very similar character are also manufactured.

How far the rate of production of dynamite will be affected by the further development of the value of Nobel's new preparation, the blasting gelatin, it is difficult to foresee, but there appears great prospect of an important future for this very peculiar and interesting detonating agent.

It is hoped that the subjects dealt with in this discourse afford interesting illustration of the intimate connection of scientific research with important practical achievements.-F. A. A.

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This fact readily explained why the process was unsuitable for wrought-iron or steel.

It was then resolved to carry out a further series of experiments bearing on this fact, and the best means of applying it practically. Pure carbon dioxide prepared in the usual way was first tried. A silvery coating of magnetic oxide was formed after an exposure of about seven hours at a dull red-heat; the coating, however, was crystalline and somewhat brittle, although very hard.

Very long and tedious sets of experiments were then carried out with mixtures of carbon dioxide and air, air and carbonic oxide, and varying exposures of the three together.

The following is the method of procedure now adopted, and which answers most satisfactorily:-The articles are first of all heated, and acted on for a certain period by the products of combustion largely mixed with air from a peculiarly constructed furnace (designed by Mr. Anthony

CHEMICAL NEWS,
May 16, 1879.

Bower), burning slack or small coal. In this way a coating of magnetic oxide is formed close to the surface of the iron, but this is often slightly covered with red oxide, Fe2O3. The admission of air to the furnace is then so arranged by a suitable apparatus that a stream of carbonic oxide is passed over the articles for a short time, and the red oxide very speedily reduced to magnetic oxide,— 3Fe2O3+CO=2Fe3O4+CO2.

reduction to magnetic oxide, is very readily detached from It is worthy of note that although the red oxide, before the iron, after the reduction the Fe3O4 so formed is perfectly hard and homogeneous. From all appearances it would seem as though a kind of fusion took place, but at the same time it must be recollected that the temperature used (a red-heat) is very low to favour such an action.

The oxide formed by this process has been tested very thoroughly, and withstands the ordinary oxidising influences perfectly.

Mr. Bower has several contracts in hand which are to

be dealt with by his processes, and will present opportunities for the practical testing of the two processes from a commercial point of view.

ON THE INFLUENCE OF
VARIATIONS OF TEMPERATURE ON THE
DEVIATION OF POLARISED LIGHT

BY SOLUTIONS OF INverted suGAR.*
By P. CASAMAJOR.

THE researches, of which I propose to give an account in this paper, were suggested by an interesting communication of Dr. Ricketts to this Society, which was presented at our last meeting.

Dr. Ricketts found that the temperature at which the deviation of a solution of inverted sugar becomes 0 is not 90° C., as given by some authors, but 92°, or rather 91-7°C. From this Dr. Ricketts concluded that if a solution of commercial sugar is inverted in the ordinary way, if originally the two constituents of the sugar were cane sugar and inverted sugar, after inversion there must only remain inverted sugar, and if we bring this solution in the saccharometer tube to have the temperature of 92° C., the indication of the saccharometer scale must be o.

As the inversion of sugar solutions in testing sugars is now almost entirely neglected, it struck me that the introduction of this subject before this Society was of great importance, as it is likely to excite inquiry in this direction, and must lead to interesting discussions which will throw much light on a ground which has not recently been explored. I hope the following remarks may be considered as a contribution to this important subject.

To enable me to present in a clear light the results I have reached, it becomes necessary to bring before you some theoretical points relating to the inversion of sugar solutions.

It is to Mitscherlich that we owe the observation that the deviating power of solutions of inverted sugar on polarised light varies with the temperature. It is, however, to Clerget that we owe a careful study of the subject. As far back as 1849 he published in the Annales de Physique et Chimie (vol. xxvi., 3rd series, p. 175) a process for rectifying errors in tests of commercial sugars by tion caused by a solution of inverted sugar, obtained by Soleil's saccharometer, by taking into account the deviaheating with hydrochloric acid a sugar solution, previously tested without inversion. In this communication, however, Clerget does not enter into theoretical considerations. He directs that sugar solutions shall be inverted by heating them with 10 per cent of their volume of concentrated hydrochloric acid up to a temperature of 68° C.,

* Read before the American Chemical Society, Feb. 6th, 1879.

CHEMICAL NEWS, Deviation of Potarised Light by Solutions of Inverted Sugar.

May 16, 1879.

taking about ten minutes in the operation. As soon as this temperature is reached, the solution is to be cooled down to some temperature between 10° and 35° C., as the table he gives for correction is calculated for temperatures between these limits, which, he says, 66 answer for all occasions which may present themselves in " Europe, as well as in the Colonies."

When Clerget proposed this new plan for making sugar analysis more correct, the subject of testing sugars was not a new one with him, for it is to him that we owe the idea of using Soleil's polarimeter as a special instrument for analysing sugar, and, as far back as 1845. he had published, in the Bulletin de la Societe d'Encouragement, an account of Soleil's saccharometer. In his paper in the Annales de Chimie et de Physique he gives no theoretical reasons for the new process. For the theory of the correction of the direct test of the saccharometer, by taking into account the test after inversion, I am indebted to some formulas in Mandlebluh's Guide (Leitfaden zur Untersuchung der Verschiedenen Zuckerarten, Brunn, 1867, p. 56). This theory I will now proceed to lay before you.

You are aware that commercial sugars contain, besides pure cane sugar, a variety of substances, of which many exert deviating effects on a ray of polarised light. Among these is inverted sugar, which may be an immediate substance or a mixture of dextrose and lævulose. This latter supposition was advanced by Dubrunfaut, but has never been demonstrated in a satisfactory manner, although it would take volumes to collect what has been written about it and is being written about it every day.

The other bodies which accompany cane sugar have not been studied in such a way as to throw light on their nature, with the exception of aconitic acid, isolated by Dr. Behr, who gave an interesting account of his researches in a paper read before the Society two years ago. A point of great importance in connection with the analysis of sugar by optical methods is that the impurities which are generally present are in such a condition that they seem to exert no effect on polarised light. The proof of this is to be found in the fact that with most sugars, particularly if the saccharometric test is above 99 per cent, the result, after the correction for inversion, is the same as given by the direct test. As many of the impurities reduce the alkaline solution of tartrate of copper, they are comprised under the head of inactive glucose, concerning the nature of which there are many unsatisfactory doctrines.

To explain how the direct test by the saccharometer may be corrected by subsequently inverting the solution on which this direct test was made, let us suppose that we have in the first instance a deviation, D. We may suppose that this deviation is the resultant of the following:

+C, deviation due to the cane sugar.

- i

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inverted sugar. one or more substances, besides cane sugar, which turn the plane of polarisation to the right.

- g, deviation due to one or more substances, besides inverted sugar, which turn the plane of polarisation

to the left.

|

213

slight, and as the impurities are in small quantities when compared to the cane sugar, the changes they suffer may be neglected, and we may suppose that, with the exception of the conversion of cane sugar into inverted sugar, no change takes place in the other constituents of the commercial sugar from the treatment with hydrochlorie acid.

After this action of hydrochloric acid, aided by heat, has taken place, the solution is examined again in the saccharometer, and, after making a deduction for the volume of acid added, we will obtain a deviation, d. This deviation in ordinary sugars will take place on the negative side of the scale. We may suppose that it is the resultant of the same elements that made up deviation D, with the exception of the quantity C, now represented by the deviation due to the inversion of the cane sugar originally present. This quantity we will call - I, and we shall have Ii + h − g = d. If now we wish to eliminate the quantities i, h, and g, we may easily do so by subtracting the second equation from the first, and we shall have C+ I = D - d.

By a series of experiments Clerget established the relation between C and the corresponding value of I. This relation varies with the temperature, but we may suppose that the observation, after inversion, is taken at 28° C., at which a quantity of cane sugar which, before inversion, gives a deviation of 100 to the right, will show for the corresponding inverted sugar 30 to the left or 30. At this temperature C + I becomes 13 × C = D - d. As dis a negative quantity the algebraic subtraction is equivalent to an arithmetical addition, whence we draw the rule that at 28° C., the true quantity of sugar C is equal to the sum of the two deviations divided by 1.3, as

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We may in the next place inquire: What are the correThis number 13 corresponds, as we have said, to 28° C. sponding numbers for other degrees of temperature? This brings us to the consideration of Clerget's table. For these numbers, and on consulting his table we find that temperatures between 10° and 35° C., Clerget determined for a quantity of cane sugar equal to 100 we must take for the quantity D-d at 10° C., the sum 139, and that for every degree C. above 10°, up to 35°, the number representing the arithmetical sum of the deviations is equal to 139 minus one-half the difference between the number representing the temperature and 10°. Thus for 20, we have 20 - 10 = 10 and 139 10 134; for 28°, we have 28 10 = 18 and 139 - 18 18 = 130; for 35°, we have 35 10 = 25, and 139 126.5, &c. If the same law should hold good below 10°, we must, to 139°, add for every degree below 10°, and this leads us to establish that at o°, the number corresponding to Dd would be 139 + 5 = 144. As this number 144 is one of great importance, allow me to recall to your attention that it means that if we have a solution of pure sugar which will produce a deviation of 100 divisions on the positive side of the saccharometer scale, if this solution is inverted by heating with 10 per cent of hydrochloric acid, this inverted solution, if tested at the temperature of o° C., will, after making the correction for the quantity of acid added, produce a deviation of 44 on the negative side of the scale.

-

25 = 2

Then we may suppose that C – i + h g= D. In this equation the only known quantity is D, but what If now we suppose that the law which Clerget found for we want to know is C. To find this quantity we make temperatures between 10° and 35° holds good for all other use of this fact, that if the solution under examination is temperatures, we may easily obtain the deviation to the heated with 10 per cent of hydrochloric acid, the whole left of the same solution of inverted sugar at any temperaof the cane sugar will be converted into inverted sugar, while the other substances will not suffer any change. this temperature in degrees Centigrade. Thus we shall ture by subtracting from 44 one half the number expressing From some experiments which I made with artificial mix-have for 10°, d= (44-5)=-39; for 20°, d--(44-10) tures analogous, as far as I could judge, to those which constitute the impurities of commercial sugars, I am led =-34; for 28°, d = − (44 — 14)=-30, and for any temperature, t,to believe that by heating with concentrated acid a certain change takes place in the deviating power of the impurities of commercial sugars. This change is, however, very

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214

Divisibility of the Electric Light by Incandescence.

If now we draw a series of parallel equidistant lines, intersected by another series of lines, also parallel and equidistant, perpendicular io the first, we may take on the horizontal base line or line of the abscisses, a space between two lines corresponding to 1° C., and we may suppose that the space between two lines of the other series corresponds to a division of the negative side of the saccharometer scale. If now, on every vertical line, starting from the base line, we take a length proportional to the numbers given by the equation

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CHEMICAL NEWS.
May 16, 1879.

clamour on telephones caused by the ordinary telegraph currents on neighbouring wires. He had tried recently the Bell telephone on a line from Dublin to Armagh, 95 miles long, but the induction noises completely stifled the speaking, whereas the Edison transmitter gave good results. The clamour could be got rid of either by neutralising the induction currents or by eliminating the noises from the speech. He had taken the second line by experiment. Since the vocal currents differ from the induction ones in potentia! and period, he attempted to make the latter discharge across the line to earth by fine needle points, and from a heated spiral of wire, in a vacuum, leaving the vocal currents to pass on to the receiver, but without success. Also, since the vocal currents are alternately positive and negative, whereas the induction ones are of one sign, he tried to avail himself of the difference in discharging power of positive and negative currents, but without success. He then tried to take advantage of the difference of period or duration of the currents, the induc

is equivalent to the equation of the right line, y=a+bx, tion currents being longer. He therefore tried to break in which d=y, a = −44, b = 1, and x=t. If now we take again our equation,

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up the inductions by interposing a rapidly rotating current interrupter, and to make the sections of the musical note obtained interfere with each other by means of an acoustic interference-tube, but practically failed in this also. He mentioned these facts for the benefit of others who may be going over the same ground.

Mr. WOLLASTON pointed out that a perfect cure for induction on underground wires consisted in twisting the going and returning wire of the telephone circuit round each other.

Mr. WILSON then read a paper "On the Divisibility of the Electric Light by Incandescence." By Joule's law the amount of heat developed in a circuit of resistance, R, by the passage of a current, C=CR; where R is the resistance of generators and connections, r, added to the resistance of the light emitter or incandescent wire, P. Therefore, since by Ohm's law,

we have

Mr. WOLLASTON explained the construction of Gower's improved form of Bell's speaking telephone. The older form, made of wood or ebonite, is open to the objections that it has a very weak voice, soon gets out of adjustment andfrom changes of temperature, and requires a twisted hand wire which is liable to break. Gower's form has a comparatively loud utterance, is constant, and does not require to be held in the hand, but may be laid on a table or hung on a wall, a speaking-tube leading from it to the operator's ear or mouth. The "call" for attracting attention is also within the Gower telephone itself; whereas, in the hand telephone it is an auxiliary apparatus. Every organ of the old telephone has been modified to form the Gower. The magnet in the Gower is of a horse-shoe form, very powerful, the two poles being brought very close together, and each pole is mounted with a small coil of fine wire. The diaphragm is much thicker and larger than the Bell diaphragm. The case is of brass, to expand equably, and a speaking-tube is fitted to the front of the diaphragm. The call consists of a musical reed attached to the diaphragm, so as to be opposite a small slit in the latter. To sound the call it is only necessary to send a sharp puff of wind up the speaking-tube, and the reed gives out a note which is heard throughout a room at the distant end. Speaking and cornet music was transmitted by the instrument exhibited, between the third storey over the hall and the meeting. It was very distinct and audible several feet from the receiver. Speaking done some thirty feet from the transmitter was also sent. Conversation was likewise carried on while considerable noise was being made in the

room.

Prof. MCLEOD remarked that the timbre of this phone was very good.

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From this equation the value of P may also be determined. CP is the amount of heat developed in the incandescent wire. He infers that the smaller the mass of the wire the higher the temperature generated in it, therefore the mass of the wire should be diminished until the fusing. point of the metal is almost attained. The question of divisibility resolves itself into our being able to divide a single incandescent source into a number of smaller ones giving the same total illumination. The author concludes that this can be done by arranging the sub-divided sources in "multiple arc," or parallel circuits, provided the total mass, length, and sectional area of the united sources be the same as in the original single source. The objection that increased radiation from the various sources would diminish the first total of light and heat can be met by making the smaller wires still smaller than is theoretically required so as to generate more heat. The author regards the "voltaic arc" as probably falling under the same law, the mass, however, being smaller in this case.

Dr. COFFIN then exhibited a Trouvé Polyscope, which consists of a small hand incandescent platinum wire electric light, designed for illuminating the more inaccessible cavities of the body in surgical examinations. The current is supplied by a Planté secondary battery, and the light is tele-half enclosed in a small silver reflector, fitted with a convenient handle. The apparatus is portable. Dr. Coffin found that it was open to several objections, which he has remedied. First, the heat generated made the lamp so hot

Prof. W. F. BARRETT then gave an account of some attempts which he had made to overcome the induction

over dose of tartaric acid, taken by mistake for Epsom salts. Poisons are conveniently classed by the author under four heads-those which cause death almost immediately, irritants, irritant-narcotics, and poisons affecting the nervous system. The fourth group is again subdivided into narcotics, deliriants, convulsives, and those producing complex nervous phenomena.

that it could not be held to the body for more than a very | taken, a fatal case of poisoning is on record from an short time. He overcame this by making the reflector of double silver plates, and circulating water between by means of india-rubber pipes from a bulb which can be worked by the patient himself, thus serving to distract his attention from the operation. Secondly, the secondary battery exhausts itself in twenty minutes, and the light therefore goes out, while from twelve to twenty-four hours are required to re-charge it. Dr. Coffin has superseded it by a Leclanché battery of 8 elements, made by Messrs. Coxetter and Sons, in which the carbon pole is replaced by a copper plate faced with platinum, and no porous diaphragm is employed. This gives a constant light for hours.

NOTICES OF BOOKS.

A Manual of Practical Chemistry: the Analysis of Foods and the Detection of Poisons. By ALEXANDER WYNTER BLYTH, M.R.C.S., F.C.S., &c. London: C. Griffin and Co.

We cannot but consider it singular that though chrome is mentioned among the irritant poisons no instructions are given for its detection. This is the more to be regretted, as chromium compounds are used in the arts on a vast scale, and are present in the waste-waters from dye and colour works, &c., whence they may find their way into streams, wells, &c. Potassium bichromate, even applied externally, often produces unpleasant symptoms-a fact very familiar wherever "chrome-blacks" are much dyed.

In the section on animal poisons we find a most interesting account of the secretion of the cobra, which the author has carefully examined. The active principle is not a "germ stable chemical compound, which Mr. Blyth has isolated or organised ferment, but a well-defined and and named provisionally cobric acid.

The whole work is full of useful practical information, and as far as we have been able to perceive it may be regarded as trustworthy. An exceedingly valuable feature -we believe original-is that the various pleas which may probably be raised on behalf of a supposed adulterator or poisoner are here pointed out, and the expert is thus forewarned. We have also very full instructions as to the channels through which different poisons may be introduced into the human system.

THE first portion of the title of this book, when standing
alone as it does on the back, scarcely leads the reader to
expect what is accurately enough described in the second
part. The work consists of two somewhat distinct sections,
the one treating of the analysis of foods, with especial
reference to their impurities-intentional or accidental-various
whilst the other is devoted to the detection of poisons.
Thus we have before us what might be pronounced two
distinct treatises, whose bond of union is mainly due to
the bookbinder.

At the same time we feel perfectly free to admit that each of these parts has been compiled in a judicious and conscientious manner. In dealing with adulterations the author has selected the best and most recent methods; he has appended certain useful legal decisions, and under each chapter he has given the bibliography of the subject. We are pleased to see that Mr. Blyth does not under-rate the difficulties of food analysis and of toxicology; he addresses himself to chemists, and does not, as some earlier writers have pretended to do, seek to make every man his own analyst.

In speaking of the analysis of milk we find that he, like most practical authorities, is able to confirm the substantial invariability of the "solids not fat" as existing in unsophisticated samples. He admits that the publication of a normal standard allows a certain amount of watering to be practised, but he fears that the bulk of commercial milk in this country is below the lowest estimate of the Society of Public Analysts. We must, moreover, warn him that it is not in all cases safe to discuss and criticise, even approvingly, published analytical processes. We have heard of one case where such criticism, which necessarily involves quotation, was met with the threat of an action for infringement of copyright! The remarks on unhealthy and abnormal milks are very interesting. The author considers it demonstrated that a disease similar to, if not identical with, tuberculosis may be propagated from animal to animal by means of the milk derived from a diseased COW. He considers that phthisis is very rare among cattle, and that when so affected their milk rapidly decreases in quantity. The chemical qualities of the milk secreted during cattle plague, pleuro-pneumonia, and anthracoid affections have not been duly ascertained.

The adulteration of tea Mr. Blyth thinks is substantially effected abroad, and is decreasing.

Turning to the toxicological section, we find a remark quoted from Dr. F. Mohr, which though mainly judicious is on one point open to question. This distinguished chemist says "What relation sal-ammoniac, saltpetre, alum, tartaric, citric, and acetic acids, &c., have to toxicology we cannot conceive." Yet, unless we are greatly mis

A defect which we hope to see remedied in a future edi. tion is the prevalence of typographical errors. The late Professor Gorup-Besanez is converted into Gorop Besaner; Crantz, the historian of Greenland, becomes "Crzaut," &c. In a tabular view of the composition of coffees from different localities, taken from a German source, some words are left untranslated. Thus we read of Jamaica and Ceylon "Plantagen." It should be "Plantations."

CORRESPONDENCE.

THE VITRIOL MANUFACTURE,

To the Editor of the Chemical News. SIR,-Dr. Lunge seems to have misunderstood the purport of my letter. I did not intend to prove that an appre ciable loss was actually experienced in the Glover tower; I wrote to point out that all fear of appreciable loss of nitre in the Glover tower had not yet vanished. published some figures simply to show the possibility of such a loss being quite appreciable.

I

It would not from my point of view be necessary to reply to Dr. Lunge at all, since his remarks flow from this misunderstanding, but as some of these remarks are directed against my ability of weighing arguments, I feel it a duty to myself to make the following statements. Until very recently the loss of nitre was by no means generally understood to be to so large an extent due to the reduction of nitrogen compounds. For example, Lock's Treatise on the Manufacture of Sulphuric Acid, dated 1879. decidedly inclines to the belief that Mr. Davis's views on the subject are the best explanations yet given of the loss of nitre. Dr. Lunge's treatise, just published in German, lays more stress on the loss of nitre incurred by reduction to nitrous oxide in the chambers. But the whole tenor of the explanations given of the reactions causing such loss is such as to produce the impression that these reactions occur only in isolated places in the chambers, viz., near the steam-jets, and is not at all calculated to give an idea of the magnitude of this loss, which Dr. Lunge now puts down at 75 per cent of the

216

The Vitriol Manufacture.

nitre used. An attempt to give a measure of the loss even
if only approximately, I have not found in this exhaustive
and very able treatise. I consider it therefore a gain to
have elicited from so high an authority as Dr. Lunge the
admission (even if conditionally only) that the amount of
nitre lost in a manner not yet clearly understood is 75 per
cent, or more, of that used.
This "big margin of course is affected by all the
errors in estimating the losses from other sources, but it
is quite certain that the statements I furnished err on the
right side. Dr. Lunge differs from me only in the distri-
bution of this "big margin." Whereas I think a portion
of nitre (and I have many reasons for thinking so) is de-
composed in the Glower tower, Dr. Lunge considers the
whole of it destroyed in the chambers. He would have
been more consistent if he had used a similar phrase to
one occurring in his treatise, to the effect that certainly
the Glover tower is in this respect no worse than any other
denitrator.

To some extent, however, Dr. Lunge seems still to think that part of the "big margin" must be accounted for by the oxidation of arsenious acid to arsenic acid in the Gay-Lussac tower, when, he remarks, that my views conflict with "very careful investigations of M. Hjeldt." | But permit me to point out that these "very careful investigations" are of the same type as Mr. Davis's. Both authors discovered arsenic acid in Gay-Lussac vitriol, both came to the conclusion that it was due to oxidation by nitrous anhydride at the expense of an equivalent of nitric oxide. Neither of the two gives experimental proof of this assertion; while Mr. Davis tries to find the resulting nitric oxide in the exit gas of a number of works, M. Hjeldt is satisfied with simply calculating the probable loss of nitre due to this supposed reaction. I have attempted in more ways than one to oxidise arsenious acid by means of nitrous acid in presence of strong sulphuric acid. I have allowed the reagents to act for seventy-two hours at ordinary temperature, and for several hours at temperatures up to 230° F., without being able to obtain a single bubble of any gas, either nitrogen, nitrous oxide, or nitric oxide. I have after repeated experiments come to the conclusion that arsenious acid cannot be oxidised to arsenic acid in presence of strong sulphuric acid so easily as to constitute a source of loss in the manufacture of sulphuric acid. Thus I am convinced that the "big margin" must be accounted for otherwise. Where the whole of the nitre is introduced into the Glover tower there remain only this apparatus and the chambers for the distribution of the loss.

Dr. Lunge thinks my fallacy consists in not having brought forward one particle of proof that any part of this "big margin must be accredited to the Glover tower, and he produced, what is no doubt meant to be an excellent proof, that the whole of it must be ascribed to the chambers.

Dr. Lunge cites the results of two French works. In one of these (Scheurer-Kestner), where no Glover tower is used, 47 of nitre per 100 of sulphur were consumed, and Dr. Lunge calculates that 75 per cent were decomposed inside the chambers. If that is really so, how could the other works (Maletra, of Rouen) where nearly the same amount of nitre was used per 100 of sulphur, save 35 per cent of the nitre, simply by introducing a Glover tower. There would on Scheurer-Kestner's basis be at the outside 15 per cent to be saved, and based on Dr. Lunge's calculation I should say that the introduction of a Glover tower in Scheurer-Kestner's works would, as far as denitration is concerned, be practically useless. Dr. Lunge evidently has forgotten to charge ScheurerKestner's denitrator with part of the loss incurred. For a saving of 35 per cent in such works is only possible if the mode of denitration formerly in use is more disastrous than that by the Glover tower.

I have no experience of any other method of denitration except that by the Glover tower, and for ought I can say to the contrary it may be the very best form of deni

CHEMICAL NEWS,
May 16, 1879.

trator, but that does not imply that the Glover tower is
perfect, nor exclude the possibility of improvement.
In estimating the share of loss of the chambers I made
use of Mr. Davis's figures. Mr. Davis defended these
very figures as those he was most sure of. I have, how-
ever, some results of daily testings extending over three
months of the exit gas of a set of chambers having neither
Glover nor Gay-Lussac tower attached, and these results
show that the amount of nitrogen escaping in form of its
acids is within a small amount (20 per cent) equivalent
to the nitre potted. All the conditions which are necessary
to cause a reduction of the nitrogen compounds to a lower
degree of oxidation than nitric oxide I conceive to be
present in the Glover tower to an equal, if not a greater,
degree than in the chambers. The sulphurous anhydride
here in its greatest concentration is associated with all
the steam evolved in the Glover tower, to react upon
nitric oxide in the nascent state at a temperature much
higher on the average than that of the chambers.
I can
see no valid reason in what Dr. Lunge has
brought forward to arrive at the conclusion that the loss
in the Glover tower has "vanished into thin air," or, as
he formerly expressed himself, is as small as a "differential
quotient," whatever that expression is meant to convey.
Still less can I see any great wisdom in so easily acquitting
the Glover tower of all share in the destruction which is
evidently going on in the system, and for which, I am
fully convinced, the chambers are not wholly responsible.
-I am, &c.,
FERDINAND Hurter.

Laboratory, Gaskell, Deacon, and Co.
Widnes, May, 1879.

THE VITRIOL MANUFACTURE.

To the Editor of the Chemical News. SIR,-I do not wish to take up more of your space than I am obliged, but it seems to me necessary to state that in testing vitriol exits by a continuous system a Bunsen pump and meter is not necessary. An 8-litre bottle properly arranged is more than sufficient for eighteen hours' work, and if that quantity of gas be drawn out in such a manner as to accurately sample the whole number of cubic feet of gases passing, one cubic foot, or even less, will serve every purpose. One cubic foot of the exit gases in many of my experiments has been a sample of at least 1,200,000 cubic feet passing away. But what I principally want to point out (and which I did point out in my last, only it seems to have vanished in transit) is that both Hurter's and Lunge's theory of the chemical loss of nitre in the chambers will not work. Hurter ascribes 20 per cent loss, due to the action in the chambers. Lunge says 75 per cent. Now let us examine both of these.

A works with five large chambers was making 100 tons of vitriol per week, and they were using to produce this 3 tons of nitrate of soda per week; they used no towers, made always a good production from the ore burnt, and the escaping oxygen was 6.2 per cent by volume of the exit gases. The total acidity of the exit gases was always low-about 2'3 grains of Na2CO3 neutralised by one cubic foot. After working in this way for some years this firm decided to erect one denitrating column and two absorbing columns: directly they started to work there took place a great reduction in the quantity of nitre used, and the nor mal quantity soon became 16 cwts. per week.

Now let us examine these results closely, and the amount of nitre destroyed by the chambers must be reckoned on the original quantity used before the towers were erected, as your correspondents have not inferred that the introduction of towers will cause the destruction of nitre in the chambers to be any less, and we have no published experiments which even hint that this might be the case. These chambers, then, actually used 60 cwts. of nitrate of soda per week.

Hurter states twenty per cent is destroyed in the chambers; this is equal to 12 cwts.

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