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name acid becomes incorrect if it implies any peculiarity of constitution, and superfluous if it does not." Now, as Laurent and Gerhardt did admit and assert that the salts of hydrogen are constituted like the salts of any other metal, and as Mr. Foster is doubtless perfectly aware that they did so, the above sentence is a distinct condemnation of Gerhardt's proposal of applying the word acid to salts with hydrogen as base. And coupled as it is with Mr. Foster's admission that these hydrogen salts ought, in systematic language, to be called hydric sulphate, hydric nitrate, &c., it does convey Mr. Foster's assent in a very full manner to the principle of the proFosal which I made on the subject of nomenclature.

The general form of Mr. Foster's paper is, however, that of an argument against my proposal; and the paper contains some statements to which my silence would probably seem to give a consent which I really cannot give. It must have been from inadvertence that Mr. Foster speaks of my wishing to apply the name acid to such bodies as CO2, SO,, SiO2, &c.; for I merely remarked that the name that belongs to them is wanted by its owners, and that it does not suit the hydrogen salts to which Gerhardt wanted to transfer it.

Mr. Foster goes into an elaborate exposition of what he conceives to be the original meaning of the word acid, and speaks of that "original meaning " as "anything but particularly clear." He might safely have called it "particularly cloudy."

to us.

Every chemist knows that the great Berzelius epitomised the prevailing definition by saying that an acid is an electro-negative oxide, and a base is an electropositive oxide. No definition is complete and perfect; but this definition is certainly clear, and it does point to differences of properties among chemical compounds which are the most characteristic and important known I cannot see any chance whatever of the words acid and base being given up; for they describe conveniently the chief differences of properties by which we classify compounds chemically. Mr. Foster's remark, that "the strictly scientific significance of the word acid has passed away," and that the word indicates "a distinction to which we now know that no real difference corresponds," must be taken as referring to Gerhardt's misuse of the word acid, as describing salts with basic hydrogen. He might have gone a step further in condemnation of that misuse of the word, and have shown that the word acid never has had any scientific significance as applied to hydrogen salts.

Mr. Foster quotes from my note (but apparently misunderstands) the statement, "In fact, he (Gerhardt) systematically applied the term acid to hydrogen salts, giving the name anhydride to acids, and leaving bases, however anhydrous they might be, entirely unprovided with a corresponding name.' If bodies such as HNO,, H2SO4, HPO were considered to be entitled to the name "acid," then for precisely similar reasons, bodies such as KOH, Ba(OH)2 would be entitled to the name "base" and if the bodies N2O5, SO1, P2O, &c. formed by dehydrating these so-called acids are called "anhydrides,' then some corresponding and distinctive name should be given to the bodies KO, BaO, &c., formed by dehydrating the so-called bases. The absence of any such term is a deficiency sufficiently grave to make one pause in adopting the term anhydride in systematic language, until the idea which it represents is duly applied to the other great class of chemical compounds; but I cannot, with Mr. Foster, call it a "limitation;" and as I have not said that Gerhardt imposed any "limitation" in the matter, I may fairly be excused from

accepting Mr. Foster's challenge to show where Gerhardt imposed it. If Mr. Foster were to deny my statement that the anhydrous bases are unprovided by Gerhardt with a name corresponding to that of anhydride for the acids, I might probably beg the favour of his quoting chapter and verse in support of his denial. But as matters now stand, the two great classes of chemical compounds are called acids (such as CO2, SO3, SiO2, &c.) and bases (such as K2O, CaO, Fe,(,, &c.), Whoever wants to take their names from them for the use of their hydrates must at least give them new names which will do as well. And he will certainly not be permitted to take the names from the two classes of bodies, and put them off with one name between them. Gerhardt seems to have thought that he would be permitted to do so, but the single substitute (anhydride) which he offered is admitted to be not only insufficient but absolutely unacceptable.

Perhaps the most important advantage which chemists have gained by representing all substances of known composition by typical formulæ, has been the increased clearness with which they have been able to compare the properties of bodies with one another, without the mind being encumbered by conventional differences of form. Even elements are now for the most part represented by formulæ analogous to those used in representing compounds; free hydrogen being HH like HCl, free oxygen being 00 like CaO, free phosphorus being P,P like H,N, &c. The one great difference which stands forth above all other chemical differences, is that which is described in various terms, all more or less similar in import to acid or acid-like and basic or base-like. We have long since admitted that this fundamental difference is a difference in the degree in which various substances exert analogous effects, a weak acid acting like a base under the influence of a very strong acid, and a weak base acting like an acid to a very strong base. Among simple and well-known compounds this difference is most markedly represented by oxides such as SO,, P2O, SO2, CO,, CaŎ, K2O, PbO, Bi,O,, &c.; and every chemist knows that compounds of the former class are electro-negative to those of the latter class, electronegative oxides being called acids, and electro-positive oxides being called bases. It is admitted that hydrogen salts must be represented and named like other salts; hydric nitrate, or hydric phosphate, like potassic nitrate or potassic phosphate, and potassic hydrate or calcic hydrate like potassic nitrate or calcic nitrate; and Gerhardt's attempt to apply to bodies of the first class the name acid is, in the words of Mr. Foster "incorrect if it implies any peculiarity of constitution [different from other salts]. and superfluous if it does not." Mr. Foster might, however, as above remarked, have added that Gerhardt's definition of the word acid is simply in itself devoid of meaning. He quotes it thus :-Acids are "salts whose base [the italics are mine] is wholly composed of hydrogen.' A person ignorant of the meaning of the words acid and base could surely not ascertain from his inner consciousness which is the acid and which the basic constituent in any of the following compounds :KOH, HNO,, BaO,H,, SO H2; and Gerhardt's pretended definition would afford him no aid in ascertaining which of these compounds are to be called acids, which bases. One is almost tempted to suspect Mr. Foster of bitter irony when he calls this definition "strictly scientific and logical." Although different in form, it is not one bit more reasonable than the Munchausen (or Irish?) feat of ascending to the moon by the aid of a mile-long chain, the traveller first fastening his chain by one end

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at a point one mile up, then climbing up by the chain to that point, and so on. But I am sorry to say that Gerhardt's disciple is even in a worse plight than the aeronaut, he is so unfortunately circumstanced that even if his chain were fastened one mile up, he could not climb up it. For if, as a preliminary to the understanding of Gerhardt's dictum, we are told how to find out which is the acid and which the basic constituent of a given compound, we find that this preliminary information is inconsistent with Gerhardt's dictum, and prevents our making any use of it. By the aid of a battery anybody could find out which are electro-negative, which the electro-positive oxides derivable from the above compounds; but Gerhardt would then reject the result as inapplicable to his purpose.

It has always seemed to me that the most plausible objection to the use of the terms acid and base in the sense of electro-negative oxide and electro-positive oxide was the fact that some acids, such as SO, P2O5, SiO2, &c., may be put in contact with bases such as BaO, K,O, &c., without manifesting any strong tendency to combine with them; and observations of this kind led some chemists to say that, in their chemical properties, these socalled acids do not behave like acids, and that it is therefore reasonable to deprive them of the name acid. Now the fact is that these acids always do combine with bases when brought in contact with them in the fluid state, and they combine with more force than that with which their hydrates react on basic hydrates. It is well known that when two saline molecules such as SO,H, and BaO,H, react on one another with liberation of water and formation of a salt, the force of combination, as measured by the heat evolved, is less than that which the acid and base exert in direct combination; for the process of double decomposition separates the water from SO, and from BaO, and in doing so absorbs just as much heat as was evolved when water combined with SO, and BaO; so that the force with which the two hydrates react on one another is by so much less than that with which SO, combines with BaO.

Mr. Foster expresses an objection to applying the term "combination" to the reaction of such bodies as anhydrous acetic acid (C2H,O)2O on water, because by a process of double decomposition the two molecules, acid and water, give rise to the formation of two new molecules; but if his objection is admitted to have weight, it applies equally to the reaction of free chlorine on free hydrogen, where two molecules of the elements form two molecules of the compound by a process of double decomposition. If such reactions as that of chlorine on hydrogen, and of anhydrous acetic acid on water, are not combinations, the word might perhaps be retained for such reactions as the combination of carbonic oxide and chlorine; or SO, and water, where two molecules unite to form one; but if Mr. Foster seriously proposes such a restriction of the word, it will be time enough to consider it. The present usage is to describe as combinations those reactions in which the resulting molecules are less various than the original molecules, as in the cases of-

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Many of these processes are known to consist of a series of double decompositions, and the fact is often | mentioned in alluding to them; but it does not seem likely that we should abandon the use of the terms combination and decomposition.

Mr. Foster has discussed in his paper what he calls the original use of the words acid and base, which is sufficiently characterised by his own words, "anything but particularly clear." He has also discussed Gerhardt's misuse of the word acid. His conclusion that the word had better be given up, would be quite worthy of serious consideration if the words were only used in those improper senses. But the words acid and base really mean something not only true, but of fundamental importance, which we are constantly obliged to consider and speak of in chemistry; and I am quite sure that it would be utterly beyond my power to take from them their established meaning, even if I wished to do so. There is at present a considerable amount of inconsistency in the prevailing use of these, as of most other scientific terms; and Mr. Foster's interesting paper affords further arguments than those which I had given in favour of abandoning as speedily as practicable the misuse of the terms which has crept into partial use through popular disregard of water in hydric sulphate, and which Gerhardt unsuccessfully endeavoured to incorporate with scientific language.

I have not discussed the proposal to call both acids and bases oxides, because it has not as yet received sufficient development to enable me to form any opinion upon it beyond the obvious objections which present themselves at first sight to so grave a change. Thus, MnO, Mn,O,, MnO2, MnO,, Mn2O, are at present conveniently distinguished by names, calling the last two acids, and the first two oxides; and so also CO and CO, are very conveniently distinguished by the words oxide and acid. Another circumstance which would alone have been sufficient to prevent my offering any opinion on this proposal is the fact above explained, that it is founded on Mr. Foster's opinion that the word acid is not clear, and is unworthy of being retained.-Philosophical Magazine for June, 1865.

University College, London, May 16, 1865.


On the Electro-Chemical Preparation of Metalloids.* PURPOSING to speak only of unpublished methods, we need not now speak of ozone. Several distinguished chemists are actually endeavouring to find some relation between the state of the atmosphere and the quantity of ozone present in it. We have never been able to admit the presence of free ozone in the air. How should oxygen, which, when electrified, attacks the metals, and all matters in the least oxidisable, respect nitrogen, water vapour, organic substances-in a word, all that the air contains? This question will not, however, be definitively settled until a sufficiently certain and special reagent for ozone be found.

Electro-chemistry is now a complete science; for all simple bodies, and for the greater number of their principal compounds, it gives a mode of preparation which, under most circumstances, is even preferable to that offered by pure chemistry. We will first pass in review the metalloids whose preparation by this means is most worthy of interest.

Nitrogen must thus be isolated in a pure state-it *Cosmos, and series, i, 595.

must, in fact, be extracted from ammonia or nitric acid; now in either case it undergoes a secondary action, resulting from the decomposition of water.

Chlorine, bromine, and iodine are easily obtained by following the same method.

The process consists in decomposing in a U-shaped tube the hydrogenated combination of the metalloids, using graphite conductors as the electrodes; the orifices of the tube communicate with washing flasks, and hence the purified gases pass into the receivers. By operating on hydrochloric acid, chlorine is disengaged from the positive pole in a state of absolute purity; it is the same when acting on a fused alkaline earthy chloride.

a bent glass tube filled with clay, moistened with a solu tion of nitrate of potash; and on the other with a metallic arch of copper and lead, the copper being plunged into the sulphate of copper, and the lead into the sulpho-carbonate. The current thus engendered is sufficiently energetic to decompose the sulphate of copper; secondary reactions, which it would be useless to analyse, are produced, and the sulphur of the sulpho-carbonate of potash, partly isolated, is deposited in the form of octahedra, with rhomboidal bases on the lead plate. By making electricity act on hydrosulphuric acid, M. Berthelot found that sulphur deposited at the positive pole did not assume this form. Electricity may then be employed, provided it is properly applied, in studying the molecular constitution of polymorphous bodies, in their various combinations. Only it is necessary that the intensity of the electric force should be in proportion to the affinity causing the combination.

It is difficult to obtain tellurium in a compact mass by the electro-chemical method; Ritter could only extract it from a saline solution in a pulverulent state. Arsenic is of all metalloids most easily isolated by electricity, for it is almost as good a conductor as a metal. By means of an apparatus (known as simple in electrochemistry), all the metalloid they contain may very rapidly be extracted from arseniferous substances. Place a solution of arsenical matter in a platinum vessel, plunge a zinc wire into the liquid, and the arsenic will appear on the platinum; by prolonging the action the whole of the arsenic is extracted from its compound. This method may be varied in different ways, and renders valuable service in medico-legal researches ; it is much superior in sensibility to the process actually in use.

Bromine is a liquid which is a bad conductor of electricity; its electro-chemical treatment requires, then, that it should be maintained in solution in water; if not, it becomes necessary to use a great number of voltaic couples. As for iodine, we know how easily iodised compounds decompose under the influence of the weakest electric current; however, to collect the iodine at the positive pole, it must be dissolved as it decomposes, for its crystals, fixed on the electrode, will oppose the passage of the current. If electricity has hitherto remained powerless to isolate fluorine, it is because physicists and chemists have been unable to find the relation existing between the constitution of fluorides and the electric force to be put in play. If chemical affinity is conquered by electricity, in the generality of compound bodies, no exception can exist. Only we must know how to apply this antagonistic force of affinity, and especially to oppose secondary reactions; it is effects of this kind which have prevented M. Becquerel's collecting fluorine. The isolation of this metalloid is considered almost impossible, because of its affinity Boron has not yet been obtained on the electrode ; for hydrogen and chlorine; M. Becquerel has, however, however, it has been electro-chemically isolated by Davy. succeeded in separating it from one of its metallic com- "When boracic acid," he says, "is exposed between two binations in the following manner :-He placed on a surfaces of platinum, receiving, at the same time, all the receiver a small platinum spiral, terminating in a point, action of five hundred pairs, an olive brown matter is and on which were deposited fragments of fluoride of formed on the negative surface, gradually increasing in calcium; the two ends communicated with two platinum thickness, and finally becoming black. Insoluble in wires, larger in diameter than that of the spiral, passing water, but soluble, with effervescence, in nitric acid. through two openings made in the sides of a receiver; Heated to redness on platinum, it burns slowly, producthese wires were connected with a Wollaston's pile coming a white vapour, which reddens litmus paper." posed of twelve elements (this kind of pile gives, as is well known, a current very powerful in intensity and in quantity). The receiver being placed on the plate of the air-pump, and the air dried, a vacuum was formed; then the electricity was called into action. The incandescence of the spiral was very vivid for several seconds; the current was interrupted, and the air allowed to enter, when the fluoride of calcium was found partly decomposed; it reddened turmeric paper, and the surface of the platinum was found covered with a greyish pellicle, seeming to indicate the action of fluorine. From this experiment it would appear possible to isolate fluorine. Induction currents might perhaps be employed with success, for it seems necessary for the decomposition of any kind of fluoride, to develope electricity more especially of tension than of quantity.

The isolated body is therefore boron, which oxidises immediately, and the electric action should cease as soon as the platinum is covered, this metalloid being an extremely bad conductor.

Silicium is, with respect to conductibility, analogous to boron. Davy was unable to isolate it, even by a pile formed of a very large number of elements. M. Becquerel has obtained crystals of silicium by combining physical and chemical forces-he took two tubes of three to four millimetres in diameter and one decimetre long; one end of each tube was filled with clay moistened with salt water. By this end the tubes were plunged into a vessel also containing salt water; into one was poured a saturated solution of gelatinous silica, in hydrochloric acid, and in the other a saturated solution of chloride of sodium; a zinc wire was plunged The electro-chemical separation of sulphur is certainly into the latter, and a platinum wire into the former not of importance for industrial chemists, but it is for communication being established between these two those studying the different physical states which may wires, an electric current was produced, the hydrobe assumed by this body in its combinations; from this chloric acid decomposed, and the nascent hydrogen repoint of view the following experiment is very inter-duced the silica; crystals of silicium appeared on the esting:

Into a glass vessel pour a solution of sulphate of copper, into another an alcoholic solution of sulphocarbonate of potash; then establish a communication between the two liquids-on the one hand, by means of

platinum, and remained so long as the current passed; they redissolved when it was interrupted.

To preserve them they must be rapidly removed, washed, and then dried in a vacuum, and kept in a tube with potassium.

DUBLIN INTERNATIONAL EXHIBITION. By CHAS. R. C. TICHBORNE, F.C.S., F.R.G.S.I., &c. (Continued from vol. xi., page 295.) PLATINUM v. GLASS.

SINCE our report upon the case shown by Messrs. Johnson and Matthey, we have received a letter from that firm in which they repudiate the idea that the manufacturers are returning back to the glass. We are very glad to learn this, as no doubt can be entertained of the superiority of the metal in many respects. The writer is also in a degree pleased that he has been the means of bringing forward a contradiction to statements and impressions which had certainly taken hold of the chemical public. The author is not a manufacturer of sulphuric acid himself, and therefore can only judge of the facts that come within his observation. We have the following passages occurring in the most important chemical report ever published, the said report being written upon the largest exhibition ever held in Europe: "Nevertheless the platinum alembics have disappeared from many of the British sulphuric acid works, and the manufacturers are returning to the old method of evaporating in glass." Again, "In Lancashire the use of platinum retorts has been entirely abandoned." These facts in connexion with a visit made by the author to one of the largest manufacturers in the kingdom (not in Lancashire), who had also given them up, were quite sufficient to justify his remarks. Against them we have a case where a manufacturer has returned a second time to the platinum. There can be no doubt that where the advantages and disadvantages are anything like equally balanced, fashion creeps in even in hard matter-of-fact practical processes, and this may account why, in Messrs. Johnson and Matthey's opinion, a retrograde movement has taken place to a certain extent; and we are inclined to think with them that it is a retrogade movement. Of so much importance does the author consider the subject (for sulphuric acid may be viewed as the progenitor of chemical products), that, having received Messrs. Johnson and Matthey's permission, a few extracts from their note are given :"We would, however, ask you to modify your views as regards the platinum system for concentrating sulphuric acid, assuring you that the statements made are essentially contrary to fact. We have never for forty years past been so much engaged in the manufacturing of platinum boilers as we have been lately. This is practically the strongest evidence of the advantage of the platinum over the glass system. . . At the pre. sent moment we can instance a manufacturer who originally worked with platinum, and was induced to give it up in favour of glass, and after incurring the expense of the sacrifice of the platinum plant, and that of setting up the numerous furnaces required for glass working, has lately taken down the whole of the latter, and is again using the platinum, assuring us that the saving in fuel alone very greatly exceeds the interest, &c., of the platinum plant... We can go further than this, and state upon well-proved statistics that the saving in fuel and working expenses and space, will in five years pay in full for the cost of platinum vessels; after which time not only is there the extreme profit over the glass system, but an intrinsic value in the plant. Also there is the advantage of great rapidity and certainty in working, and above all, of absolute safety to the workman employed... It may interest you to know that a committee of the directors of some of the Continental manufactories lately visited England for the express purpose of reporting upon the two systems, and after a thorough investigation, although they came with a strong

prejudice in favour of glass, they have unanimously reported in favour of platinum system. .. We should be sorry for an erroneous opinion to be promulgated on this subject, although this may be considered rather an interested statement on our part.-We are, dear Sir, yours very faithfully, JOHNSON, MATTHEY, and Co. -C. Tichborne, Esq., Dublin."

Scientific Instruments (Continued).—The following firms show fine specimens of scientific instruments, but and barometers:-Mr. S. Yeates, Dublin; J. H. Dallprincipally cameras, microscopes, surveyors' instruments, meyer, London; Crouch, Bros., of London, who also show some very fine microscopic photographs of a considerable size. More is frequently to be gained from the study of these photographs than by ocular examination of the object when in the microscope. H. Webb, of Birmingham, shows what appears to be a very fine collection of microscopic objects, as far as an opinion can be given without an examination under the instrument. Field and Sons, Birmingham, exhibit their wonderfully cheap microscopes.

John Young, of Dalkeith, shows moulded carbon for electric batteries. This gentleman first undertook the task of making a series of experiments in connection with the above subject at the request of several gentlecarbonaceous material (coal, 8:c.) is ground to a very men interested in the progress of electrical science. The fine powder, moistened, and moulded into the form wished, in a similar manner to the making of bricks. The forms so moulded are then slowly dried, and, when dry, packed into iron moulds, and subjected to a bright heat in a close oven. The effect of the heat is to drive off the whole of the bituminous matter, leaving a dense and compact coke in the moulds. The pieces are then boiled in pitch, and again charred along with a charge of coal in a gas retort. This is repeated several times, until the required density is attained. They are then ground into the proper shape, and smoothed on the surfaces. They with coal, the latter being used to produce carbonaceous are then kept for twelve hours in a gas retort, along Vapour, which saturates and closes the pores in the coke. When the process is properly conducted, the carbons are taken out, possessing a close metallic steel-grey surface. They are much more porous than retort carbon, by which they acquire high electro negative qualities.

We must not forget to notice the patent flexible diaphragms for covering the surface of liquids which would be affected by the atmospheric oxygen. This patent includes vessels wholly lined with sheet indiarubber, or having a diaphragm which floats loosely upon the surface of the liquid. The liquid is hermetically sealed to the extent of the non-porosity of india-rubber, but we believe that this substance is still capable of allowing the diffusion of gases to a limited degree.

The following few articles that we are about to notice cannot be classed as scientific instruments, but still possess such interest in a technical point of view that the present article would hardly be complete without touching upon them. One of them is Messrs. Morton's patent refrigerator. This arrangement may be viewed as a worm, except that the wort or liquids to be cooled are made to traverse the exterior of the metallic tubes, in which is circulating the cooling medium. This apparatus consists of a series of flattened tubes made of strong copper (tinned), and connected at the ends alternately by the caps, so as to admit of a continuous flow of cold water inside the tubes. The whole is fixed to a copper case, and secured in a strong wood frame. The worts are admitted at the other end, and flow in an opposite


July 7, 1865


direction to the water alternately under and over the tubes, this motion being produced by the longitudinal ribs on the top and the corrugated bottom. The absolute necessity for the rapid cooling of worts, says the circular, ON THE PRESENT STATE OF THE CHEMISTRY is now fully recognised by all brewers who have made the chemical laws which govern vinous fermentation their study.

The applications of graphite-or black lead, as it is sometimes called-have become more numerous of late; thus it is extensively used for electric purposes, the glazing of gunpowder and shot, black lead pencils, and last, but not least, the making of plumbago crucibles.

The Patent Plumbago Crucible Company exhibit specimens of their crucibles, so well known to metallurgists. Mr. Brodie's well-known and beautiful process of disintegrating graphite has enabled the most inferior qualities of that mineral to be made available. The Plumbago Crucible Company, however, purify their graphite by passing chlorine through it when heated to redness, or in some cases simply by separating the iron, which is the great impurity, by magnets. The graphite so prepared answers their purpose as well as Mr. Brodie's, and is less expensive.

It is stated that a large deposit of graphite has recently been discovered by an enterprising Frenchman, M. Alibert, in the Batougal Mountains of South Siberia. It may be mentioned that the higher class graphite in this deposit is accompanied by an inferior variety which, as it appears from experiments made by Mr. Valentine, can be easily purified. The Siberian plumbago is not much used at present by the Plumbago Crucible Company, as it contains too much iron, and although this could be entirely removed by the company's patent process, it is found cheaper to work with Ceylon plumbago, which contains but little iron. The graphite used by them contains 98 per cent. of pure carbon. The company exhibit Ceylon, Siberian, and other graphites in their case.

To show the importance of this branch of manufacture the following facts may be cited :-The consumption of Ceylon graphite at the Battersea Works has had an extraordinary effect upon the price of the article. When the company commenced business it cost about 10l. per ton, but now it cannot be bought at double that price. In Ceylon applications to dig graphite are daily on the increase, notwithstanding the rate of 148. per ton which has to be paid as royalty at the Colombo Cutcherry. The following figures, giving the amount of revenue collected at Colombo and Galle, on account of royalty, in 1862 and 1863, clearly show the extraordinary increase in demand for Ceylon graphite:

Increase in 1863 from 1862.

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Western Province. Southern Province. The total quantity of graphite exported from Ceylon in 1862 was 40,195 cwt., of which no less than 34,730 cwt. was shipped to Great Britain. The Patent Plumbago Company are the principal consumers of the latter. M. Dierick writes the following of these crucibles:"Each crucible runs from forty to sixty pourings, and can with safety be dipped in cold water when at a red heat, and used again immediately as if it had not undergone any change of temperature; the metal is also fused much more rapidly, saving time, fuel, labour, and waste. The saving of metal is also very great, as to each worn crucible there adheres a certain amount of metal; the commoner the crucible, the greater the absorption

and adhesion."

M. Dierick, Master of the French Miut.


By HENRY LETHEBY, Esq., M.B., &c. Delivered at Birmingham, before the Society of Gas Engineers. GENTLEMEN, I propose that we should continue tonight our inquiries into the chemistry of gas lightingthat, in fact, we should extend our investigation into the subject which was commenced at the meetings of this Association last year at Manchester, when, as some of you will remember, I directed your attention to the chemical principles involved in the manufacture and purification of coal gas. On the present occasion we will examine the of the most important constituents of coal gas. leading physical, chemical, and photometrical properties

Briefly to recapitulate the subjects of the last lecture, I may remind you that we inquired, in the first place, into the composition and probable origin of the material out of which gas is produced-coal; that we then examined the leading constituents of the several varieties of coal which are best suited for the manufacture of gas, especially directing attention to the form in which the most objectionable impurity (sulphur) of coal existed. We also considered the phenomena of carbonisation or distillation of coal, and saw how much it was influenced by temperature, and how, under the influence of heat, the elements moved from their old states of combination into new. We then discussed the composition of raw gas as it of the constituents marked in the following table : leaves the retort, and I pointed out to you that it consists Constituents of Raw Gas.

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be regarded as impurities, and I pointed out to you that Now the whole of these constituents above the line may the taking of these impurities out of coal gas, in order to effect the perfect removal of them, involved a proper order, as it were, of purification-that, in the first place, both science and practice pointed to the fact that the condensation or cooling of the gas should not be too sudden; that the longer the gas was kept in contact with tar and ammoniacal liquor before it went to the condensers the better. It had been seen in numerous instances that a long hydraulic main, extending a considerable distance from the retorts, always effected the condensation of naphthaline as well as objectionable sulphur compounds; and I further pointed to the fact that when the gas had traversed the condensers it was never fairly purified if it left them at a higher temperature than 60 Fahr. The aim, in fact, should be slow but complete condensation by ceeded 60° the ammoniacal liquor was never of its full gradual cooling, for if the temperature of the gas exstrength, and much sulphur, ammonia, carbonic acid, and aqueous vapour passed on to the purifiers, where such impurities were seriously in the way.

The next question is how to remove from the gas the

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