100 VIII.-On the Chemistry of Sugar Rejning. Discourse delivered before the Fellows of the Chemical Society February 4, 1869.1 By DR. WALLACE, F.R.S.E. Glasgow. THEscience of chemistry embraces 80 wide a range of subjects that there are few men who possess sufficient versatility of mind or endurance of body to undertake the study of every one of its numerous departments. Hence we find that while all chemists regard original research as the highest aim of the profession there are many who have rendered good service to the science as literary chemists teachers of chemistry analyti- cal chemists assayers metallurgists and manufacturers. The Chemical Society has necessarily and very properly been chiefly occupied iu the promotion of original work but it has occa-sionally given some countenance to the scientific study of certain manufacturing operations and I think I may say that the publication in the Journal of the papers or discourses on such subjects as the manufacture of glass by Mr.Chance and the application of certain forms of furnace to the making of iron aid steel by Mr. Siemens has given great satisfaction to a large section of the Fellows of the Society especially those who are non-resident a large proportion of whom are interested in technical chemistry. In this country unlike Germany and France chemical technology receives no official acknowledg- ment from the State nor fkom the universities and the thanks of those interested in that important branch of the scienee are due to this Societ'y for the eiicouragement it offers to the pro- secution of study and research in technical subjects.While therefore I feel grateful to the Council of the Society for afford- ing rrie the honour of delivering a discourse here this evening I feel that I need offer no apology for bringing before them a subject of high utility and one which possesses many points of interest to the scientific chemist. The considerations which have induced me to bring before you the chemistry of sugar refining are these:-First the industry is one of very great importance ;secondly the trade has for some years been affected seriously by foreign competition; and thirdly the refineries in London formerly the principal seat WALLACE ON THE CHEMISTRY OF SUGAR REFINING.101 of refining in this country have for some time suffered from a very great depression in some cases almost threatening annihilation. As regards the extent of the industry in this country a few statistics will suffice According to the Board of Trade returns for 1868 the importation of sugar of all sorts amounted to 594,656 tons or in round numbers 600,000 tons. This is charged at various rates of duty but if we take 9s. per cwt. as the average the total revenue to the State from the import of tmgar will amount to nearly 53 millions and the total money value of the sugar including duty to about &21,000,000. I am not able to state what proportion of the quantity I have mentioned enters into direct consumption and how much is refined but I think I am safe in saying that at least 400,000 tons per annum are refined in this country.The competition of foreign countries particularly France is entirely in loaf sugar the quaatity of which imported in 1868 was 34,039 tons while the previous year it amounted to 42,047 tons. This is an alarming fact and one that de- serves the earnest attention both of our refiners and of our legislators. Either our refiners are f'iar behind in the march of improvement in manufacturing processes or the French refiners possess an unfair advantage in the fihape of drawback on duty which is equivalent to a premium offered by the French Govern- ment to the exporter of loaf sugar. That the latter is the fact I have attempted to show in a discourse recently published and I will not occupy our time with a repetition of it.If our refiners are really backward in adopting means to keep up with the times they deserve to succumb to the superior knowledge and skill of their continental neighbours ; but if the other ex- planation of the enormous importation of loaf-sugar is the true one then our Government ought to take stepa to have the cause removed and our own countrymen put on terms of equality with the French refiners. Besides the drawback on duty to which I have referred the French have a protective duty on foreign refined sugar which makes it impossible for our refiners under any circumstances to export refined sugar to France. Then as to the depression of the trade iii London I think it depends upon a number of circumstances but mainly upon the extraordinary development of the industry within the last few 102 WALLACE ON THE CHEMISTRY OF SUGAR REFINING.years in Greenock and Glasgow. In 1857 the quantity of sugw refined in the Clyde was 38,336 tons while in 1867 it rose to 178,013 tons or considerably more than four times the amount. Last year the quantity refined was rather less being only 171,643 .tons but even this ie fully two-fifths of all the sugar refined in the United Kingdom. At present there are twelve refineries working in the Clyde viz. ten in Greenock and two in Glasgow besides three standing idle or building and besides these there was refined last year about 11,000 tons by one house in Leith. Now there are in London twmtyrefineries in Liverpool eleven in Bristol four or five in Plymouth two in Manchester two in Newcastle-under-Lyme one and in Dublin one; but of those in the metropolis a considerable number are doing nothing.It appears to me that the London refiners generally have been somewhat tardy in adopting the most recent improvements introduced in the provincial refinei<eR and they have been unwilling to give up the making of loaf-sugar which has not lately been profitable for the reason I have named; and besides they work under the disadvantages of dear labour and water not particularly well suited for the purpose; and above all they are prevented from reburning their own charcoal and have to send it out to people who make a distinct trade of it.Thus while in Greenock it costs 3s. 6d. to reburn a ton of charcoal the same costs in London fi-om 228. 6d. to 25s. thus inducing the refiner to use less charcoal than he would otherwise be likely to do. The description I shall give of the process of refining mill refer to crushed or soft sugar and chiefly to the Greenock system the principal peculiarity of which is that no syrup is produced; all the sugar leaves the refinery as it came to it in the solid form and the loss consisting of insoluble matter compounds vege- table and mineral abstracted by the charcoal and loss in working do not amount in all to more than 5 per cent. Whether this system is theoretically a correct one I am not prepared to say but at all events it has been commercially successful; and the precision and rapidity with which the work is done appear to me to place rrugar refining at the summit of perfection as a manufacturing process and one which might with great ad- vantage be imitated in many branches of technical chemistry.WALLACE ON THE CHEMISTRY OF SUGAR REFINING. 103 sugar Refining. In refining raw sugar it is very important to make a proper selection of the raw material. The qualities are very various and each kind is adapted for a particular system of refining. In the Greenock system for example in which no syrup whatever is turned out it is absolutely essential to use sugars containing only a moderate amount of uncrystallisable sugar say not exceeding on the average 3 or 4 per cent.; but where a consider- able quantity of syrup is produced the quality of sugar is of less importance and concrete and low sugar such as spup Mauritius Jaggary and Manilla may be used. Mixtures are often judicious such as beet sugar with sorts which contain much fiuit sugar but in the Greenock system a large proportion of beet must be avoided as the soluble salts accumulate in the lowest kind of the refined product and communicate an objectionable taste besides retarding crystallisation. In pur- chasing sugars for refining several points demand attention. The absolute quantity of cane sugar is important as determining mainly the proportion of refined capable of being produced; and the fruit sugar and salts as preventing to a large extent the crystallisation of the cane sugar demand attentive considera- tion.The extractive matter determines chiefly the amount of animal charcoal required as well as the amount of deterioration of the charcoal. The insoluble matter when excessive is trouble-some to wash and some kinds of insoluble matter are dificult to filter stopping up the pores of the cloth which the her particles pass through and are afterwards deposited in the char- coal to its great detriment This irJ particularly the case with Home kinds of East Indian sugar. The analysis of sugar is very simple to those who have some practice in this kind of work and most of our refiners pay great attention to this branch of their business. Many of them have qualified chemists in their refineries while some employ a pro- ferssional analyst.I have myself made aboiit 400 analyses of raw sugar chiefly for refiners in Greenock and the following table contains a few results of analyses of some of the varieties of raw sugar used by refiners :- 104 WALLACE ON TffE CHEMISTRY OF SUGAR REFINING. O& d -------_. ---~ Cane eugar .. 92.35 92-31 90.41 90.80 89.00 84.20 67.00 47.0 88 -31 Fruit sngar .. 3-38 4.06 3.84 4.11 5.85 8-45 11 -36 20.4 4 -82 Extractive &c. -66 '66 '95 -77 *76 1*70 1'93 2.7 a94 Soluble salts.. -62 *37 *86 *92 *62 1 *I0 -76 2'6 -80 'Insoluble .. .. -15 *04 '22 '20 *06 -15 -73 Water .. . . .. 2-84 2.56 3'72 3.20 8.72 4'*55 18-80 2y.3 4 -40 ,----___ 100.00 100'00 100*00100~00 100 -00 1 1 1 1 ;; 1 1 CoIour,D.S.] 13 13 10 10 .. 8 Cane sugar 12-obtainable 85.9 8614 82.3 82-1 7Q-2 51..*8 13.6 79 -6 -These analyses muet not be coneidered as typical of the various kinds of sugar for all of them vary exceedingly; but they give a fair idea of the description of sugars used in refineries where crushed sugar is made. Several of the lower sorts are unfit for refining on the Greenock sygtem. The French mode of determining the value of raw sugar is upon the whole a very fair one and is based upon two assump- tiom namely lst that each perceatage of fruit or uncrystal-lisable sugar prevents the crystallisation of an equal amount of cane sugar ; and 2nd that each part of soluble salt prevents the crystallisation of five times its weight of cane sugar.My own experiments bear out the general accuracy of these assump- tions. To value a sugar or find the amount of extractable cane sugar in it we take the total amount of cane sugar as deter-mined by chemical analysis or the polariscope and deduct from it the fruit sugar and five times the soluble salts and the remainder is the quantity required. Thus take as an example a sample of Paraiba sugar containing 84.9 cane sugar 6 of fruit sugar and 1.2 of soluble salts the obtainable cane augar from this variety would be 72.9 per cent First Operation. 8olutioK The first operation in sugar refining is dissolving or what is technically called LL blowing-up,'' from the circumstance that WALLACE ON THE CHEMISTRY OF SUGAR REFINING.105 ai 5 c-.l B 4 84 -90 86 *80 86 00 87.06 86.73 79.00 74.60 76.53 72.60 94.30 87-80 6 -00 5 '03 6.35 6.95 6 05 11.76 16.13 13 38 13.95 -25 -33 1 .28 1 ,72 1 *62 *65 1 .29 1 .32 1 -70 54.47 2.11 -27 95 1 -20 1 *21 1 -44 -68 -88 1-95 1 .61 1-86 1 35 1.30 5.92 1 *lo 2 -01 -63 -54 5 -52 3 .04 5 -34 5 -52 100 900 100 .oo 100 a00 100 -00 I ~ 6 6 76.3 57.5 open steam was formerly used in the process producing a violent agitation and blowing noise. Although I do not purpose to detail the mechanical arrangements of the sugar refinery yet I must mention briefly some particulars in order that the chemistry of the subject may be understood. The different floors of a sugar house generally six or seven are arranged so that in the process the sugar passes down fiom one to the other.Acting upon this principle the sugar is hoisted to the top story or garret where it is removed from the hogsheads boxes baskets or bags in which it is imported and shovelled through holes in the floor into the blow-ups which are situated on the floor below. These vessels are cast-iron pans about 4 or 5 feet high acrid from 6 to 10 feet in diameter. At some distance fiom the bottom leaving room below for a series of steam pipes is a false bottom perforated with holes upon which the sugar rests until it is dissolved and both above and below this shelf revolving arms are moved by machinery so as to keep the liquor in constant motion. The operation is commenced by placing in the pan a sufficient quantity of water or thin liquor turning on the steam to the heating-worm and then filling in the sugar as quickly as it can be knocked out of the casks.If the blow-up is well constructed the filling should be completed in half an hour when the gravity of the liquor should be about 28' Baumd (or 1-225sp. gr.) and the temperature as nearly as possible 180° F. The liquor consists of about two parts raw 106 WALLAUE ON THE CHEMISTRY OF SUGAR REFINING. augar to one of water and a pan of 10 feet diameter will dis-solve at each filling about seven or eight tons of raw sugar. During the heating a scum iises to the surface which is skimmed with nearly flat perforated ladles but the amount of flocculent and insoluble matter so collected is very trifling.Such is the simple process as conducted in most of the Clyde refineries but elsewhere the liquor undergoes in the blow-up various kinds of treatment with the object either of removing a part of the colouringmatter of neutralising the trace of acidity in the sugar or of facilitating the subsequent process of filtra-tion so as t.0 produce a perfectly clear bright liquor. It is a very common practice to add a sufficient quantity of milk of lime or sucrate of calcium in such quantity as to neutralize the acidity of the sugar and although this is not done in some of the best conducted refineries yet I consider it a useful addition provided too much lime is not used for if excess is employed it tends to deepen the colour of the liquor and to give the char- coal additional work.Again blood was formerly much used for clarifying as it coagulates by heat producing flocculae which enclose and carry down fine particles of mud or other insoluble matter. The coagulated albumin also abstracts a small propor- tion of the colouring matter for which it has a strong attraction. Instead of blood the solid albumin obtained by evaporating the white of eggs or the serum of blood at a low tempemture has been used and has the advantage of not being quite so filthy as blood; but all these bodies which make the syrups very impure are now generally dispensed with. Various other sub- stances have been used instead of blood such as a mixture of sulphate of alumina and lime which forms a gelatinous precipi- tate of alumina but is objectionable on account of introducing calcic sulphate soluble tricalcic phosphate and soluble phosphate of alumina and lime.The greatest objection to these mixtures is the danger of the common workmen who are necessarily entrusted with the application of them using excem of one or other and so ma.king the liquor acid or alkaline and thus doing more harm than good. Above al1,it does not appear to be absolutely necessary to add anything to the liquor and many of the first refiners use no chemical agent whatever. For the removal or partial removal of the colour of the sugar ths dust of animal charcoal is sometimes introduced and if it is quite new that is not used in sugarrefining previously it has a good WALLACE ON THE CHEMISTRY OF SUGAR REF"& 107 effect.The charcoal can only be used once however as it gete mixed up with the insoluble matter of the sugar. The next operation is a purely mechanical one and consists in passiiig the solution of sugar through twilled cotlton filter bags of about two feet diameter crushed into coarse canvas sheaths of about 6 inches in diameter. These bags are 6 or 8 feet long and are fastened to the number of 200 or so to the bottom of a shallow tank into which the liquor is run from the blow-up pans and they are surrounded by the sides of an iron box so that the liquor is kept hot and also that steam may be introduced to keep up the temperature. Decolorising of the Syrup. The next operation after having obtained the saccharine solution clear anti bright is to remove the cofouring matter and this is effected by bringing it in contact with animal charcoal otherwise called bone black.This variety of charcoal has been found by practical experience to be the most suitable for sugar refining. Many kinds have been tried some of them as decolori- sing agents much more energetic than bone-black but none of them have been found to possess that peculiar combinatioii of qualities which is required-freedom &om soluble salts and from considerable quantities of calcic sulphate or carbonate sufficient density to sink readily inthe heaviest sugar-liquor and at the same time great porosity ;together with such a degree of hardncss that it will not suffer sensible deterioration by being ahovelled about and reburned every fourth day for several years.These qualifications exist in no kind of charcoal in such a marked degree as in that from bones. An artificial mixture of clay and some form of carbon has indeed been made which is said to rival animal charcoal but as I have heard nothing of it lately I fear that it has not been found so ad-varitageous as was expected. The only kind of charcoal I have found at all to approach that from bone is the kind made from certain kin& of sea-weed but even this variety is wanting in some of the characters necessary for refining sugar. Other decolorizing agents than charcoal have also been proposed. Sulphurous acid has been tried repeatedly and pro- cesses are published eveiy two or three years in which ite use is adyocated each writer apparently ignorant of the fact 108 WALLACE ON THE CHEMISTRY OF SUCIAR REFINING.that his results are already well known. St best it only removes about three-fourths of the colouring matter and the liquor requires to be treated with charcoal just as much as if sulphurous acid had not been used. It is true that sulphurous acid does not alter cane sugar like most other acids but it i8 very liable to change into sulphuric acid; and although this may be neutralized with lime still the calcic sulphate is very injurious to the charcoal which must afterwards be used. With regard to the bleaching action of ozoue I have made no experiments myself but I understand that its application has not as yet been practically successful and even if it were found economical in bleaching the colour still it would not enable us to dispense altogether with charcoal and I fear its oxidizing action would be likely to prove troublesome.Upon this point however I am not qualified to give an opinion as I have not had an opportunity of seeing the process in operation. The carbonatation process as applied in the continental factories where sugar is made from the juice of the beet and which is attended with excellent results has not so far as I know been applied on the large scale to the process of refining raw cane-sugar and I do not think its application would be advantageous. The sugar solution for this process requires to be rather dilute and consequently would require to be boiled down before passing through the charcoal for it would not be a substitute for charcoal but only an adjunct to it.I have made careful trials of the process with dark sugar and have found little or no benefit from it as regards colour although it makes the liquor beautifully clear and bright. I think how-ever that in certain cases it might be applied with good results as for instance in purifying the washings of animal charcoal which are very impure and very troublesome to deal with and also to bag filter washings and any other impure products of the process of refining To those who are not acquainted with the carbonatation process I may describe it very briefly. The sugar dissolved in a sufficient quantity ofwater is mixed with milk of lime the quantity depending upon the colour of the sugar to be treated and after being brought up to a moderate heat carbonic gas is passed through the liquor until the lime is completely carbonated after which it is boiled to decompose the calcic bicarbonate ;and the precipitate then becomes grainy and settles readily.In the beet fa-ctories the process is repeated WALLACE ON THE CHEMISTRY OF SUGAR REFINING. 109 with a smaller quantity of lime after which the juice is boiled down to 20° or 23O B. and passed througb charcoal. Impure saccharine products such as bag filter and char washings and low syrups much contaminated with salts may also be purified by precipitating the sugar as a sucrate of calcium or barium and afterwards separating the base by car- bonic gas or in the case of baryta by sulphurous gas.I consider it an excellent arrangement to have connected with every large refinery a smaller one immediately adjoining it where all im-pure products are separately treated and worked up separately from the sugars made in the refinery proper. As a preparation for the decolorizing process it has been proposed to wash or digest the raw sugar with alcohol before dissolving in water and this idea has been tried on the large scale in Belgium but has been discontinued. Theoretically the treatment of raw sugar with alcohol appears to be highly ad- vantageous. The quantity of cane sugar in a pure form obtain- able fiom raw sugar is very much reduced by the presence of soluble salts and fruit-sugar the former preventing the crystal- lisation of five times its weight and the latter of an equal weight of cane sugar.By the use of alcohol together with a minute quantity of hydrochloric or acetic acid to act upon the calcic salts present the whole of the impurities with the ex- ception of some of the colouring matter may be removed and nearly pure cane sugar obtained. But in practice there are serious difficulties to be overcome. A very pure and nearly absolute alcohol milst be used andthe expense of maintaining this would be considerable and the inflammable nature of the spirit is a serious objection; but under any circumstances it would be quite out of the question unless the spirit were obtained free of duty.A moderate sized sugar-house would require something like 10,000 gallons of spirit to start with and the duty on this alone would be about as many pounds sterling and as this quantity would require to be re-distilled every day there would be a considerable and unavoidable loss. The process has long been used for testing raw sugar and most successfiilly but the possibility of its successful application on the large scale has yet to be demonstrated. Filtration tlwouglz. Chawoal. After this rather lengthy digression we retuim to the process of sugar refining as it wtually exists. After being made clear 110 WALLACE ON THE CHEMISTRY OF SUGAR R;EFININU. and tranrrparent by passing through the bag filters the liquor is in into iron tanks or cisterns filled with animal charcoal where it is allowed to settle for several hours after which it is slowly drawn off below while more of the dark coloured liquor is run on to the top so asto keep the cistern full.As this goes on the liquor which comee away at first perfectly colourless becomes after a time distinctly yellow and the sugar solution is replaced by the syrup from a previous refine; and lastly this is washed out with hot water until no appreciable trace of sugar can be found in the washings; then the charcoal is further washed with a copious volume of boiling water next with some cold water and afterwards drained removed from the cisterns and taken to the kilns to be reburned. Such in few words is the decolorizing process which however I must now describe in greater detail.The cisterns are of various fbrms and sizes; some are square and shallow some of great depth 40to 60 feet and so on; but the kind universally employed in the Clyde refheries are circular and of no great depth being generally about 9 feet diameter and 16 feet deep and capable of containing from 20to 25 tons of charcoal according to its density. The cisterns are covered on the top and are constructed to bear the pres- Sure of a considerable column of water or liquor which may be applied when necessary to cause a more rapid filtration. The quantity of charcoal to a given weight of sugar varies exceedingly. Where water is scarce or dear coals dear and above all where the charcoal has to be sent out of town to be reburned the quantity of char is necessarily reduced as far as possible but in other circumstances the proportion should not be less than 25 cwt.of char to a ton of sugar. The size or “grist” of the charcoal must depend to some extent on the shape and size of the cisterns; but in all cases where it is possible to use it a small size such as would pass through a sieve of 20 meshes to the inch but would be retained by one of 30 meshes should be chosen. Theoretically the smaller the gist the better the finest dust being the best of all but prac- tically the char must have a sufficient size to permit the liquor to pass through it in a reasonable time. Then as to the quality of the charcoal it would occupy an entire lecture to go fully into that department.The whole subject is fully dis- cussed in a lecture which I delivered last year in Glasgow WALLACE ON THE CHEMISTRY OF SUGAR REFINING. 111 and which will be found in the Proceedings of the Philosophical Society of Glasgow (vol. VI. part 4) also in abstract in the “Chemical News.” On the present occasion I can only refer to some points connected with this most important subject. Animal charcoal when new consists of carbon calcic phosphate and carbonate and minute quantities of some other substances ; the composition is a little variable but the following results of analysis of three varieties will convey a good idea of its usual constituents A being made from ordinary bones col- lected in this country; B from South American shank bones and C from what are called camp bones which are frequently buried for some years before they are collected.Dry. Carbon nitrogenous.. A. 9.71 B. 7-64 C. 10.37 Calcic phosphate &c.. 80.48 84.05 78.70 Calcic carbonate. . .... 8.82 7-61 8.05 Alkaline salts. .. . .. -Calcic sulphate ..,.. . *34 *30 *20 -25 *53 -58 Feii-ic oxide -12 Silicious matters . . . -23 ... ..... -15 *lo -21 1.56 100~00 100~00 100~00 Cubic feet per ton (dry) 51 49 47 The above analyses represent the charcoal as being dry in order that they may be compared with one another but prac- tically the article is always sold with about 10 per cent. of water. The so-called carbon in animal charcoal is not by any means pure for it contains a very notable amount of nitrogen and a small proportion of hydrogen the quantities of both of these elements depending upon the degree of heat to which the charcoal has been exposed in the process of manufacture.Generally the quantity of nitrogen is about one-tenth part of the total carbonaceous matter but sometimes I have found it considerably more. The proportion of hydrogen in well-burnt animal charcoal is exceedingly minute being in one particular case (new) only 0034 per cent. Old charcoal which has been frequently used in refining and reburned contains less nitrogen and the proportion appears continually to decrease. I have 112 WALLACE ON THE CHEMISTRY OF SUGAR REFINING. found it as low as .3 per cent. and as the charcoal which gave this amount was not excessively old I have no doubt it may be reduced even further.I believe that the nitrogen is an important and essential constituent of animal charcoal and it is certain that no description of charcoal which does not contain an appreciable quantity of nitrogen is a good decolorizing agent. Wood charcoal for instance although eminently porous and an excellent absorbent of gases is a very poor decolorizing agent and is practically useless. Red-hot animal charcoal quenched with water evolves ammonia and I believe that the practice of cooling charcoal in this way pursued by some refiners is a highly injurious one. New charcoal always contains traces of ammonia but the amount is extremely minute being in a particular case only -011per cent.The effect of this minute quantity and of traces of sulphide of ammonium is readily seen in the sugar iun over new charcoal which should never be used until after it has been well washed and reburned. New charcoal also contains invariably a minute quantity of sulphide of calcium and gives off the odour of ‘hydric sulphide when treated with an acid and even when moistened with water. In a particular case a sample of new charcoal gave -08 per cent. of hyclric sulphide when treated with an acid. Charcoal both new and old retains appreciable quanl ities of gases which escape when cisterns containing it are filled with liquor and these gases frequently expIode when a light is brought near the top of the cistern. In a sugar-house the charcoal is usually burned every fourth or fifth day and is thus reburned from seventy to ninety times in a year.Old charcoal has not the same chemical compofiition as new. The carbon almost invariably increases and if the kilns are perfectly tight ought to increase so that the pores are gradually filled up with the deposit of carbon arising from the carbonizing of the vegetable matter extracted from the raw sugar which it has been employed to purify. This deposit of carbon is a very great evil in sugar refining and should be pre- vented as far as possible by washing the charcoal with boiling water before reburning. In some refinerieR the proportion of carbon does not increase and in others it speedily diminishes so that it sometimes does not exceed 2 or 3 per cent.When this decrease takes place it arises either from the admis- WALLACE ON THE CHESIISTRY OF SUGAR REFINING. 113 &on of air to the charcoal while hot or from excessive burning which causes a reaction to take place between the carbon and the elements of water resulting in the formation of carbonic gas and marsh gas. But if the kilns and cooling boxes are tight and the heat not excessive the carbon will inevitably increase rapidly unless we ta-ke the precaution of washing out of the charcoal before reburning nearly all the organic matters absorbed from the sugar liq-uor. Extensive washing has also a most beneficial influence in rernovi'ng mineral salts absorbed from the raw sugar. In all raw sugars a certain proportion of mineral salts is found varying in ordinary cane sugam from 4to 1per cent.in syrup sugars from 1to 2 per cent. and in beet sugays such as are used by the British refiners from 1+ to 7 per cent. The highly soluble saltg such as those of potassium have no effect upon the char- coal and only annoy the refiner by accumulating in the syrups ; but calcic sulphate a salt only slightly soluble in water is readily absorbed by charcoal and can only be removed by extensive washing. It is rather a sinplar fact that so long as the sugar liquor is strong the sulphate is absorbed and retained; but whenever the washing begins it comes away in the wash- ings so that it is no uncommon thing in boiling down weak char washings to obtain a plentiful crop not of sugar but of gypsum.When the water is hard and contains much calcic mlphate the proper washing of charcoal becomes almost if not quite an impossibility; and I have myself examined char- coal which contained 2+ per cent. of that compound. In beet factories where lime is freely used in clarifying the juice the pores of the charcoal soon become choked with calcic carbonate rendering it useless unless the compound is removed by treat- ment with an acid. But charcoal becomes old and useless from another cause ; it gradually shrinks in volume and the pores must become either lessened or altogether obliterated. The space occupied by a ton of new charcoal when dry is usually about 50 cubic feet but after being a few months in use it is reduced to 40;and so it goes on ghrinking until it reaches 28 cubic feet which is the densest charcoal out of about 400 samples that I have tested.Now this does not arise from an actual increase in the density of the charcoal. Ihave tried the specific gravity of old and new charcoal and have found the difference very slight indeed. Thus VOL. XXII. K 114 WA4LLACE ON THE CHEMISTRY OF SUGAR REFINING. new charcoal occiipy-ing50.6 cubic feet per ton had a gravity of 2.822 while t'he old occupying only 35 cubic feet had a gravity of 2.857. The fact is that the heat to which the char is subjected produces a semi-fixion of the calcic phosphate which is its most abundant constituent and causes a shrinking in the bulk of the particles. The following siniple experiment serves to illustrate this point.A quantit'y of new charcoal measuring 48 cubic feet per ton was exposed in a covered crucible to a rather strong heat for an hour after which it had contracted to 43.2 cubic feet ; after two hours more to 40.8 cubic feet ; after other four hours it measured 38 and with still four hours longer of a strong heat 35.5 cubic feet; thus losing in eleven hours as much of its porousness as it woiilcl by being worked in a sugar house for two years. It is well known to chemists that oalcic phoaphate is fusible at a high heat but the temperature of a charcoal kiln is sufficient to produce only agglutination. New charcoal burnt white has the appearance of bits of chalk but old char- coal has the texture of porcelain or flint.The quantity of liquid capable of being retained by the two kinds is also remark- able. If a funnel is filled with good new charcoal perfectly dry and water poured on it as long as it is retained it will be found to hold in its poreq from 80 to 100 per cent. while old charcoal retains from 30 to 45 per cent. according to its quality. Again dry new charcoal does not become perceptibly wet unless at least 20 per cent. of water is added to it while old charcoal is made wet with 5 per cent. All these considerations point to the necessity of renewing the charcoal very frequently in order that it may act efficiently. It is not enough merely to replace the dust that is sifted out occasionally and to make up by the addition of new char for the shrinkage in volume that is constantly taking place.If proper work is to be done and the charcoal maintained in a state of real efficiency a portion of the entire char (not the dust only) should be set aside from time to time and replaced by new material at the rate of 50 per cent. per annum and the addition should be made constantly; one two or three bags of new charcoal in every cistern according to its capacity. As regards the proper quantity of charcoal to use per ton of augar that depends a good deal upon the kind of sugar used and upon the quality of the charcoal; but the smaller the quantity of charcoal the better for the use of a large quantity WALLACE ON TEE CHEBIISTRY OF SUGAR REFINING. 115 entails a loss of sugar and the production of an extra propor- tion of weak and impure washings.For a ton of sugar 25 cwt. of charcoal is amply sufficient if the quality is good and if fine sugars are used an equal weight is enough. It is a mistake to suppose that a large quantity of bad or exhausted charcoal will serve the same purpose as a moderate amount of good charcoal. Not only does it occupy more space and SO limit the production of refined sugar but it does not in any quantity do the work so well besides producing an overwhelming amount of ‘6 sweet water,” or charcoal washings. I have found that it is impossible on a practical scale to wash out all the sugar from charcoal so as to make the washings worth boiling down and that for every 100 parts of charcoal there is it loss of *75 of sugar.If therefore an equal weight of charcoal is used the loss of sugar will be -75 per cent. while if two tons of charcoal are used for each ton of sugar the loss will be 16 per cent. from this source alone. I have selected a few analyses of specimens of old or used charcoal which will coiivey an idea of the variety to be found in different sugar-houses throughout the country. D. E. F. cf. H.I. K.L.M. Carbon nitrogenow 9 74 10.60 12.86 19.64 7.42 10 63 5.82 17 28 2 56 Calcic phosphate .. 82 8u 83 20 81-80 73.20 87-08 80 56 77.26 792~90.73 Calcic carbonate ,. 5.92 4.15 2 92 3.18 1-92 4.52 14.66 1.06 3.50 Calcic sulphate.. .. *67 -64 -42 1.12 .95 2 24 1 03 -59 1 10 Ferric oxide . . ,. ,. *33 -55 .67 66 -85 *72 *21 -69 1-17 Silicious mattera .. *54 -86 1 .33 2.20 1 .’i8 1.32 1.02 -83 -94 100 00 LOO *00100 ,oo 100so0 100 .oo 100 .oo 100 -00100-00100-00 Cubic feet per ton. . D is first-class charcoal; E is of excellent quality; F is of fair average quality; G is pretty old and very much glazed; H is very old and overburned; I has been used in a sugar-house where hard water is employed; K has hen used in a con-tinental beet factory; L has been soured in the process of washing; and M has been exposed to the air while cooling. The power which charcoal is capable of exerting in removing colouring matter from solutions is truly astoniahing. A very good lecture-room experiment consistrj in pouring into a funnel 116 WALLACE Oh' THE CHEMISTRY OF SUGAR REFINING.filled with good animal charcoal an aqueous solution of cochi- neal vhen it comes through perfect,ly colourless and its presence in the charcoal in an unaltered form may be illustrated by boiling the charcoal with alcohol when it gives up the colouring matter to that liquid. Port wine may be used for the same purpose and with a like result,. Charcoal has also the power of absorbing vegetable albumin gum oxide of iron calcic carbonate and hydrate and calcic sulphate. In sugar we have vegetable albumin extractive matters and invariably some salt of calcium and all these as well as the colouring matter are removed by the charcoal ; and not only so but their removal is important and essential so that if we could practically bleach sugar by ozone chlorine sulphurous gas or any other chernical agent we should still require to use charcoal to purify the sugar.The active ingredieiit in animal charcoal is unquestionably the iiit.rogenous carbon for if the charcoal is burned perfectly white not only on the outside of the grains but to the very centre of each particle it no longer retains the slightest trace of decolorizing power. But it is quite evident that the carbon owes its extraordinary powers to its extreme porosity the carbon being infinitely cornminut'ed and kept asunder by admixture with ten times its weight of calcic phosphate. The dark-brown solution of raw sugar comes away at first perfectly colourless; after a time the pores of the charcoal begin to get saturated and the liquor gradually becomes yellow and even brown if the process is continued long enough.The sugar refiner takea care to economize hi8 charcoal by passing through it first a fine quality of raw sugar afterwards an infeiior sort and lastly syrups from the drainage of previous refines. The calcic carbonate in charcoal is very useful in neutralizing the minute quantity of acid present in almost all raw sugars and also the acids always formed during the washing of the charcoal by a process of fermentation which it is very difficult to prevent. Charcoal deprived of all or nearly all its calcic carbonate is very objectionable and is sure to give rise to sour liquors and the occurrelice of iron in the syrups When the water used for dissolving the sugar and for washing the charcoal is very soft the calcic carbonate gradually decreases until in pretty old char it is reduced to 1Q per cent.and even in extreme cases disappears entirely. On the other hand when very hard water is uaed the calcic carbonate either decremerr WALLACE ON THE CHEMISTRY OF SUGAR REFIXING. 117 very slightly or it increases and sometimes to an alarming extent; and in beet factories on the continent wliere lime is freely added to the juice the eril is a very serious one. In this case it closes up the pores and many expedients have been adopted for the purpose of getting rid of it. This is done; either by washing with I or 2 per cent. of hydrochloric acid diluted with a sufficient quantity of water to saturate the char or better by Mr.Beanes’ process which consists in impreg- nating the burnt charcoal with perfectly dry hydrochloric gas until it is saturated then exposing it to the air until the excess of the gas escapes and lady washing with water and burn- ing. In beet factories and in some particular circumstances in refineries also when the liquors are slightly alkaline the process is attended with the best results but I have always objected to the use of acid in refineries using soft water for there the calcic carbonate instead of being in excess is barely sufficient to neutralize the minute quantity of acid in the raw sugar. That animal charcoal treated with an acid gives a whiter liquor than it would otherwise do is easily demonstrated ; but on the other hand it appears from my own experiments and those of others that it is impossible to get rid by mere wash- ing of every trace of acid; and the consequence to be feared is that the sugzr in the liquor will be to some extent converted into fruit sugar during the process of boiling down that the char washiugs will be very soar and the syrups contaminated with iron.In other words I believe that in a refinery working under ordinary circumstances less syrup is produced than would obtain if the charcoal were treated with hydrochloric acid while in the latter case the colour of the sugar produced would be superior. It may be interesting to mention that while dry hydrochloric gas passed over dry calcic carbonate does not give rise to any action whatever the dry gas passed over absolutely dry charcoal containing calcic carbonate de- termines the complete decomposition of the latter especially if.the charcoal is warm. Bean es’ process and others of a similar nature may be applied with advantage to new charcoal for the purpose of bringing it at once into efficient working condition. New charcoal contains traces of ammonia and sulphide of ammoniuni and also some fkee lime besides an excessive quantity of calcic carbonate; and although the ammonia is removed and the free lime carbonated by the processes of washing and KfL 118 WALLACE ON THE CHEMISTRY OF SUGAR REFINING. re-burning to which it ought always to be subjected before being employed in sugar refining yet the excess of calcic carbonate makes the liquors very yellow and it is usually five or six weeks before the charcoal is in first-rate condition.When however the new charcoal is added in small proportion to the old there is no danger of any harm resulting but on the contrary an immediate advantage is observed. The oxidizing power of charcoal is well known to chemists and although this property is useful in purifying water and in deodorising yet in sugar refheries it is the cause of much mischief. When the char cisterns of a refinery are to be washed off hot water is run on while the heavier syrup descends and is drawn off below. But the two liquids commingle to some extent and a weak solution of sugar is formed which is exceedingly liable to fermentation. The free oxygen in the washing water under the influence of the charcoal appears to act upon the vegetable albumin which the charcoal has extracted from the sugar converting it into a ferment which quickly changes the sugar into lactic acid and this acid dissolves from the charcoal lime and traces of iron.The consequence is that the char washings are sour and putrid and highly charged with salts of calcium besides which they frequently smell perceptibly of hydric sulphide. The ordinary way of getting rid of these washinq is to use them for dissolving fresh sugar but no greater mistake in sugar refining than this could be made As regards the temperature best adapted for the action of charcoal on sugar experience has shown that the liquor in the blow-up pans should be run off at 180' F.the char cisterns should have a temperature of about 155' and never below 150° and the water used for washing should be absolutely boiling. The quantity of water employed in the process of rehing is say for 100 tons of sugar something like this :-for dissolving 50 tons; for washing to produce sweet washings to be after- wards boiled down or used for dissolving 40 tons ; for washing the charcoal to purify it further 125 tons-in all 215 tons or nearly 50,000 gallons. I consider this the minimum quantity ; an additional amount of washing is invariably attended with increased excellence in the quality of sugar turned out. Revivifying of the Charcoal. The re-burning of charcoal in order to restore toit the power of absorbing colouring matter and other impurities is perhaps WALLACE ON THE CHEMISTRY OF SUGAR REFINING.119 the most important process in sugar refining. The object to be attained is to carbonize the organic matter extracted fkom the raw sugar so far as it has not been removed by washing. The process should be economical as regards fuel; it should allow of tfhe complete carbonization of the organic matters; it should permit of the ready escape of the gases and vapours produced; and it should expoae the charcoal for only the smallest possible length of time to the heat required for car- bonization so as to avoid the contraction of the pores of the charcoal besides other evils that result from overburning. There are two distinct kinds of reburners; those in which upright pipes are used and those which consist of hoiizontd revolving cylinders.The kiln hi general use consists of a series of upright; cast- iron pipes arranged in six rows of about ten pipes each row three rows being placed on each Ride of the furnace. The flame of the furnace plays directly upon the pipes and the pro-ducts of combustion are conducted away from the sides of the kiln. The wet char as it comes from the cisterns is placed upon the top of the kiln and sinks gradually down as the burnt char in the pipes is allowed to fall into the cooling boxes below. These consist of sheet-iron vessels the same length as the row of pipes to which they are attached about six or eight feet deep and an inch or three-quarters of an inch wide and cooled simply by contact with the atmosphere.The cooled charcoal is drawn from the cooling boxes every twenty minutes in such proportion that it is about six or eight hours in the pipes altogether. The time gven should depend upon the heat of the kilns and different quantities should be drawn fiom each row of pipes according to the amount of heat they receive from the fire. Thus if there are three rows of pipes the one nearest the fire should be emptied in about 5 hours that in the middle in 73 hours and the back row in 10 hours. These kilns although tolerably economical as regards fuel are open to many objec- tions not the least of which is that the wet charcoal above pre- vents the fiee escape of the gases and vapow evolved from the carbonizing and drying charcoal.Of the heat consumed in the kiln four-fifths are absorbed in drying and it is a great mistake not to dry the charcoal wholly or partially before putting it into the kilns. I cannot occupy more time with further details of the various mechanical arrangements which have been adopted by various sugiir rcfiners nor with the description of 120 WALLACE ON TKE CHEMISTRY OF SUGAR REPUTING. the various forms of revolving cylinder-kilns information about which will be found in my paper on charcoal previously referred to. When the charcoal is sufficiently cold it is again placed in the cisterns and the whole process is repeated. Evaporation of the Liquor. The next process in sugar refining is the boiling down of the decolorized liquor so as to recover the sugar in a cryatalline form.This as is well known is effect>ed by means of a vacuum pan in which the vapour that is formed is condensed by jets of water and thevacuum is maintained by means of an air-pump. A pan of good size is 10 or 12 feet in diameter and may hold about 20 tons of sugar and syrup. The boiling down occupies usually about two or three hours; the extent of vacuum averages in a well made pan about 28 inches and the tempera- ture is usually 120’ F. at the beginning of the boiling and about 130’ at the end of the process. The improvements intro- duced of late years into the vacuum pan consist in increasing the extent of heating surface and the quantity of water injected into the condenser and in enlarging the neck of the pan to 18 inches or even more so as to permit of the free escape of the vapour into the condenser.The operation commences by running into the pan a quantity of liquor s&ciel;t to cover the first coil of steam pipe or ‘‘ worm,” when the steam is turned on and the boiling commences. After a time more liquor is run in and go on a little at a time until the pan is full the different tiers of worm being supplied with steam as soon as they are covered. At the very first the liquor is boiled strong enough to form a tb grain,” consisting of almost microscopic crystals of sugar and these increase in size as the boiling proceeds until at the finish they are as large as may be desired. It requires a considerable amount of training and skill to boil sugar so that the grain may be gradually built up.What is called false grain consists of a mass of minute crystals collected into grains and although in some cases this kind of compound crystal results fr9m the carelessness or want of skill of the boiler in other iiistances it is made intentionally so as to give the resulting sugar a whiter appearance and to enable it to hold more syrup. When IYery large and distinct cfystals are deaired such as WALLACE ON Tm CmWSTRY OF SUGAR REFINING. 121 are made in Bristol and Glasgow a modified arrangement is adopted. The liquor is boiled more slowly and at a higher temperature and when the pan is full the whole contents are not drawn off but onlya half and this is repeated several times the crystals becoming larger every time.The large crystals are much prized on account of their beauty and purity but they have the disadvantage of being troublesome to dissolve while the manufacture of them necessitates the exposure of the syrup with which they are mixed for a long time to a rather high temperature (about 160’) causing the conversion of a con-siderable portion of sugar into the uncrystallisable form and also darkening the colour of the syrup. And here I wouldgive a word of advice to refiners who all insist that in order to obtain large crystals a high temperature must necessarily be employed. I believe this to be a mistake. If sugar requires a high temperature to form large crystals it must be different from all other crystalline bodies; and besides sugar candy is formed at a low degree of heat and consists of larger and more distinct crystals than ever were formed in a vacuum pan.Large crystals must be formed slowly and the degree of heat is I believe a matter of indifference. Strange to say I have not succeeded in inducing any refiner to boil slowly and at o low temperature. They all say that it cannot be done and so the matter rests. The mistake they makeis that they regulate the rapidity of boiling not by the quantity of steam admitted to the worm but by the quantity of injection water so that when the latter is diminished the extent of x-acuum is lessened and the temperature necessarily rises while the steam not escaping readily retards the process of evaporation.If on the other hand the maximum quantity of injection wdter were maintained and the amount of steam diminished the boiling would be as slow as inight be desired while the loss to the refiner by exposing the syrup to a high temperature would be avoided. In boiling down the syrup obtained from the drainage of the first crop of crystals less care is required a small grain being preferred on account of carrying more syrup than a larger grain. In boiling the lowest grade of syrup it is customary to make what is technically called a “jelly,” in other words the formation of grain is entirely avoided and the result is left for several days intanks in order that crystals may form. There are generally three qualities of crushed sugar made viz.,whites mediums and yellows the white8 constituting nearly half of the entire produce ; but the proportions of the different kinds vary to some extent with the kind of raw sugar employed.The total produce of 100tons of raw sugar should not be less than 95 tons. The separation of tlie crystals from the syrup with which they are mixed is effected in an apparatus called a centrifugal machine which is simply 8perforated basket revolving at great apeed so that the periphery travels at something like 100 miles an hour. The drainage of the crystals occupies from three to twenty minutes according to quality and in the case of the finest and whitest variety a dash. of cold water is sometimes given in order to wash off the adhering syrup.And now I must bring my lecture to a close and have to thank you for the kind attention you have given to the sub- ject. Ifeel that I owe some apology to the scientific chemists present who must have listened I fear with impatience to details iu which they can have felt little interest. I have endeavoured to avoid mechanical details as far as possible while trying at the same time to exhibit a connected view of the whole process; and to the sugar refiners who have favoured me with their presence I have to say that it is impossible in a single lecture to give anything like rz complete description of all the improvements that have duriug the last few years been intro- duced much less to describe the results of the investigations connected with this branch of industry with which I have been engaged.The field of inquiry is one that is sure to be fruitful of valuable result8 to any careful observer and I trust that my few remarks if not. otherwise useful may at least have the effect of attracting attention to a subject of great importance. At the conclusion of the lecture the Pr esiden t directed attention to the observations that had been made on the con- densation of the charcoal in re-burning. He observed that charcoals not containing phosphate of lime if they are subjected h a long-continued heat-which need not be very intense- eadually contract and become quite hard. He had found from his own experience that charcoal which has been produced in a very light and porous condition gradually contracts on long exposure to heat just as gold precipitated in the porous state by a ferrous salt becomes compact and acquires a metallic ap-pearance if heated far below its melting point.WALLACE ON THE CHEiWSTRY OF SUGAR REFIXIKG. 123 The use of lime in sugar refining really appears to bring the sugar into an uiicrystallisalole state and the power of crystallisation is not restored by addition of an acid though it is recovered spontaneously after a certain time. The action both of acids and of lime and alkalies appears to destroy the crystallisability of the sugar and therefore an excess of either should be avoided. In connection with the decolorization of sugar which appears still to be entirely dependent upon the absorbing power of animal charcoal the President directed attention to the great absorbing power for colouring matters possessed by sulpliide of lead as observed some years ago by himself in the case of a solution of cochineal &om which it entirely removes the colour- ing matter although he by no means intended to recommend such a substance for use in sugar refining.Dr. Hugo Muller said that the sulphide of lead cannot be used with advantage in liquids like sugar; indeed Dr. Scheib- ler has recently found that it is dissolved and retained by several liquids of that kind and cannot be separated from them after wards . Mr. Pearson stated with reference to the quantities of sugar imported into this country that Holland as well as France sends large quantities and that unrefined as well as refined sugar is abundantly introduced.He mentioned the case of a sugar refiner in London who about a year ago was refining at the rate of 400 tons per week of beet-root sizgar imported from the Continent. With regard to the washing out of the charcoal Mr. P e ars on observed that in the north where there is an abundant supply of pure water this process may be carried to a very great extent ; but in the south where the waters those of the metro- polis for example generally contain a considerable quantity of calcareous salts a limit is very soon attained the charcoal after a certain time actually abstracting these earthy matters from the wateq which consequently runs off purer than when it is put in.The President enquired if any gentleman present could inform the meeting whether the colour-absorbing power of animal charcoal remains the same aft,er the phosphate of lime contained in it has been removed by hydrochloric acid ? 124 WALLACE ON THE CHEMISTRY OF SUGAR REFINING. Dr. Hugo Muller said that he had found from his own ex-periments in filtration that the pure charcoal though actually stronger in its action than the ordinary bone-charcoal is not so in proportion to the quantity; in fact that the same quantity of charcoal when the bone-phosphate is removod from it is not so strong as if it contained the bone-phosphate. Mr. Williams said that he could fully corroborate this state- ineiit fiom repeated expeiiments of his owii ; that though the pure charcoal will of course do more than the common charcoal bulk for bulk there is no comparison in the real percentage action of the carbon in each case.Dr. V o el c ke r asked for information respecting experiments made by Mr. Beanes on the decolorizing effect of ozone upon sugar. Mr. B e a n e s replied that the ozone process is not yet sufficiently advanced to enable him to speak positively respecting it ; but that so far as his present experience goes ozoiiized air passed through a coloured syrup for three hours exerts a decolorizing action as great as that obtained by leaving the sugar in contact with animal charcoal for twenty-four hours. Professor Williamson observed that one of the most iin- portant points which have lately occupied the attention of sugar refiners is the relation believed to hold good between the quantity of solnble salts in the unrefined sugar and the quantity of crystallisable sugars retained by them in the mother liquid and prevented from crystallising.It is custornaiy now to estimate the quantity of such salts in the sugar and to deduct a proportionate quantity of the sugar as being unavailable. From experiments made in his own laboratory by a gentleman occupied in the matter it appeared that some salts possess the property of retaiiiiiig sugar in solution as such while others Beem to possesa the opposite property actually accelerating the separation of the sugar. Dr. Voelcker mentioned that beet-root sugar generally con- tains a considerable quantity of chloride of sodium and yet no fruit-sugar is found in it,whence it seems to follow that chloride of sodium has not the power of changing the nature of the sugars.That it to a great extent prevents the crystallisation is however a well-known fact ; indeed sugar-refiners dread the presence of common salt in their sugar8 more than that of almost any other salt.