the cane-juice all those substances which are likely to injure the quality of the sugar by their mechanical mixture with it; or those, the presence of which would, if long continued, inevitably produce some chemical change in its saccharine principle, and thereby either diminish the quantity of sugar which ought to be obtained, injure its quality, or produce both these results.

Those substances are, as before stated:-1st. Insoluble impurities, consisting of small particles of earthy matter, bruised pieces of cane, chlorophylle, &c. 2d. The proteine compounds, albumen and caseine. 3d. Soluble coloring matter. 4th. Salts. We possess no means of getting rid of the last mentioned, as I have before had occasion to state.

The separation of the first, or insoluble impurities, can be effected by means purely mechanical. In the West Indies these matters are permitted to run into the clarifiers, as we know, and are separated only subsequently to the application of heat. But this plan always entails a loss of cane-juice, which is retained in a considerable quantity in the bulky scum at the top and the thick sediment at the bottom. This loss may be prevented, and a better defecation obtained, by submitting the cane-juice to a coarse straining, rather than a filtration, previously to its going into the clarifier.

Filtration of the cane-juice, antecedent to its passage into the clarifier, has been repeatedly practised, and discontinued, in consequence of its either being too tedious an operation, or from the difficulties which have attended it. The object of filtration at this early stage, it should be remembered, is merely to separate the coarser insoluble particles suspended in the cane-juice. It must be performed so rapidly that the means employed shall offer no impediment to the free transmission of the passage of the liquid, or add to the risk of decomposition ensuing. For this purpose a large doublebottomed sieve should be suspended over each clarifier, the meshes of which should be formed of metal wire of an inch apart in the upper one, and of an inch in the one below. When the sieve is foul, after each filtration, the upper bottom must be removed, and the adhering impurities washed out.

30

The removal of the proteine compounds, albumen and caseine, and the soluble coloring matter, cannot be effected so easily; for this purpose we must call in the assistance of chemistry. The only chemical agents at present employed are heat and lime.

The first coagulates, and renders insoluble the vegetable albumen which at the same time envelopes and entangles a large quantity of the flocculent particles suspended in the liquid, and thus assists considerably their separation, in the same way as the white of an egg, or the serum of the blood, when added to liquids that it is wished to clarify. Heat, alone, however, is insufficient to produce those effects upon cane-juice which are understood by the term defecation. Syrups obtained from cane-juice thus treated would show little disposition to granulate, while they would have a strong tendency to decompose. Experience has shown this to be the case; therefore, from time immemorial, the application of heat has been assisted by

the addition of lime, or an alkali obtained by the incineration of some favorite vegetables. Both soda and potash, either in their caustic states, or as carbonates, defecate cane-juice equally as well as lime; but the great injury that their presence would inflict upon the sugar and molasses, renders them inadmissible for this purpose. The action produced by caustic or recently slaked lime on canejuice, is a very complex one; and I believe we are at present far from thoroughly comprehending it. It merits attentive consideration. When a drop or two of the milk of lime be suffered to fall into a tumbler of cane-juice, the color of the latter is immediately changed from a greyish green to a bright yellow, on the spot where the lime has fallen. This change of color is accompanied by the separation of the liquid into two parts, the one being a solid heavy precipitate, formed by the collecting together of the insoluble impurities; the other, being the cane-juice rendered tolerably clear by the separation of those substances.

Lime saturates any free acid it may meet with in the cane-juice; it sets free a small quantity of potash; it forms an insoluble compound with a portion of the cascine, which is either precipitated, or which rises to the surface in the scum; it combines with three times its weight of sugar-the substance produced being very sparingly soluble in cold, and still less so in hot water; it deepens the color of the juice.

When the cane-juice contains a small quantity of lactic and acetic acids, an event which occurs more frequently now than formerly, owing to the want of a sufficiency of labor to hasten the stages of the manufacture, the lime combines with those acids, and forms uncrystallizable salts, which preserve a portion of the sugar with which they may be in contact in a fluid state.

Should a small quantity of glucose be present in the syrup, which is always the case when concentration has been conducted as it now is in the colonies, the lime, probably assisted by a small quantity of potash which has been set free, speedily converts it into glucic acid; and the glucates, when formed by the prolonged action of the heat, are as quickly converted into melasinates of the same bases, and the whole syrup is thus rendered of a dark brown or black color.

Cane-juice, defecated as judiciously as possible by means of lime and the application of heat, throws down a further precipitate on the addition of a little diacetate of lead.

It might be supposed, that as lime and heat alone are insufficient to produce the entire separation of all injurious substances from the cane-juice, and, as the employment of the former is far from being entirely innocuous, that its use ought to be dispensed with, and that some other substance ought to be substituted for it.

We have seen, that many substances are capable of throwing down caseine from its solution in cane-juice, more or less completely; but the action of some of them is less complete than that of lime; and others are inadmissible, either in consequence of the ulterior injurious effects which would be produced on the sugar, or from their poisonous qualities. We are therefore compelled to con

tinue the employment of lime, either alone, or, still better, associated with other substances which promote its powers; and, consequently, enable us to use it in quantities so small, as to remedy many of the evils which result from it as at present administered.

1. Defecation by means of lime, and subsequent filtration. The first thing to be attended to, is the quality and method of preparing the lime. This substance ought to be as pure and free from admixture with silicious or other foreign bodies as possible. It should be carefully burnt, and immediately slaked with boiling water, which should be added in such a quantity as to form a mixture of the consistence of cream, and the whole should be strained through a fine wire sieve.

The cane-juice, previously strained as before recommended, having been received into the clarifier, heat is to be applied to it as quickly as possible. In the meantime, its acid reaction should be tested by means of litmus paper, so that we may form an idea of the quantity of lime which will be required. Usually, the acid reaction is slight, but decided; that is, the litmus paper is changed by it from a blue to a reddish purple or purplish red; but cane-juice presents great variations in this respect, and with the amount of variation will depend that of the lime to be added.

The temperature of the liquor in the clarifier having risen to about 130°, a measure of the milk of lime, containing from four to six ounces of pure burnt lime, is to be added, and the whole intimately blended together by means of an oar for a minute. The liquor must be again tested, and, if necessary, an additional quantity of lime must be given to it, until it presents a perfectly neutral reaction; that is, until it neither changes the blue color of the paper to a red, nor that into blue, which has been previously made red by the vapor of vinegar. The heat is to be continued until perfect ebullition has been established for two or three minutes. The cock of the clarifier is then to be turned, and the liquor passed directly into the filters.

Each clarifier is supposed to contain 300 gallons. The filters which may be employed, are either the common bag filters or the charcoal filters, both of which will be explained presently. The latter, however, is an operation uncalled for in this stage of the manufacture of sugar from the sugar-cane, if the defecation has been carefully attended to.

From the filters the liquor should pass directly into the coppers, whenever this can be accomplished. Unfortunately, as the generality of boiling-houses are arranged, this is rarely practicable, in which case it must run into a cistern constructed for the purpose, and be pumped from thence into the pans.

When carefully performed, and the quantity of lime accurately given, this method is a very good one, and answers very well if the cane-juice be good, healthy, and freshly expressed.

When the quantity of lime has not been quite sufficient, so that the liquor has a slightly acid reaction, the color of the sugar will be light, but the grain small; on the other hand, if the liquor be slightly

alkaline, the grain of the sugar will, cæteris paribus, be bolder, firmer, and larger, but the color will be darker.

Whatever be the kind of vessel employed to perform the above, or any of the succeeding modes of defecation, it is essential that it shall be constructed of copper. The ordinary clarifying pans of the West Indies are all formed of this metal; but some of those which have been latterly introduced, and which have been constructed on the same principles as the blowing up cisterns used by refiners, have been made of, or lined internally, with iron; and I need not say, that they are, in consequence, unfitted for the performance of many of the most successful methods of defecation about to be described.

2d. Defecation by nutgalls. To two ounces of nutgalls, finely bruised, add half a gallon of boiling water; infuse for twelve hours, and strain; neutralize, by means of cream of lime, a clarifier of cane-juice containing 400 gallons, and when the temperature is about 150° to 160°, add the infusion of galls; mingle the whole together by means of a ladle or an oar, boil for three or four minutes, and filter through bag filters.

This method may be followed with advantage when the cane-juice is viscid, without increased acidity.

3d. Defecation with sulphate of zinc. To a clarifier containing 300 gallons of cane-juice, previously deprived of its insoluble impurities by straining, add, as soon as possible, twelve ounces of sulphate of zinc; apply heat, and when the temperature has risen to 150°, add as much milk of lime as will render the liquid neutral, or, in the slightest degree, alkaline; boil for two or three minutes, and filter through bag filters.

There are few substances which defecate better than sulphate of zinc, employed in this manner. But it must be remembered, that this substance is poisonous, and, whenever used, it is absolutely necessary to filter the liquor through bag filters, which retain the sulphate of lime and insoluble oxide of zinc, in combination with the organic matters that have been acted upon; while the defecated liquor passes through free from any deleterious admixture.

4th. Defecation by means of alum. Dissolve four pounds of common alum in a sufficient quantity of pure water, and when the cane-juice in the clarifier (350 gallons) is just beginning to get warm, pour it in and mix well with an oar or ladle. The cane-juice will now have a strong acid reaction, and the heat must be quickened, as much as possible, to 1409, so that neutralization may be effected by the addition of milk of lime, added in repeated doses, until the litmus paper is no longer altered. Boil and filter as before. Common alum is a combination of sulphuric acid, alumina, and potash. In the above operation, the lime has set free the alumina, which immediately combines with the coloring matter; and the free lime and sulphate of lime, produced by the decomposition which has taken place, precipitate almost entirely the other organic substances of the cane-juice, leaving the sugar unaltered. We could, therefore, desire no better means of accomplishing our object, were it not that the sulphate of potash is retained in solution in the cane

juice, and its operation on the syrup and sugar, ultimately obtained, would be injurious.

5. Defecation by means of the sulphate of alumina. This substance is employed in the way just described for alum. It does not contain potash, but is composed of alumina and sulphuric acid only. The proportions required are about one pound to every 100 gallons of juice; but twice, or even thrice that quantity, may be given with advantage. We must be careful, however, to neutralize the liquor, thus treated, as quickly as possible with milk of lime, otherwise some risk would be incurred of converting a portion of the sugar into glucose. Every pound of the sulphate of alumina will require about seven or eight ounces of caustic lime to effect its decomposition; but a slightly additional quantity may be given in all cases, beyond what is merely necessary, although the liquor may thereby be rendered slightly alkaline.

I can conceive no better method of defecating cane-juice than this. The liquor as it comes from the filter is almost colorless; and all the after processes to which it is submitted are extremely satisfactory. I have produced sugar from caue-juice thus acted upon, equal in color to the finest clayed Havannah, and possessing a sharp and sparkling grain.

Unluckily, the sulphate of alumina is not an article of commerce in this country, owing to there being no demand in it. It can, however, be obtained from France, where it is used in the manufacture of beet-root sugar. We possess by the decomposition produced, three defecating substances of considerable power; namely, the alumina, the sulphate of lime, and the free lime which has been added in excess.

The application of this plan is attended with little expense, and no trouble; and the results obtained are, as I have just stated, such as to recommend it for general adoption.

6. Defecation with the sulphates of alumina and zinc. A combination of these two substances may occasionally be employed, I think, with some benefit. A few experiments induce me to advise a trial of the plan, if merely to ascertain in what respect the results obtained differ from those of the last. The proportions used by me have been, one pound of the sulphate of alumina, and two ounces of the sulphate of zinc, to 100 gallons of juice. The way of proceeding is exactly as above, and the lime must be added as indicated by litmus paper.

7. Defecation by means of alumina and sulphate of lime. This method is one which has been pursued with some advantage by refiners, both in this country and in France. Two pounds of common alum are to be dissolved in about two gallons of water, either in a wooden or earthenware vessel; purified chalk, which is a carbonate of lime, is slowly to be added, and the two intimately mixed together. When all effervescence is over, and does not recommence on the addition of a little more chalk, the decomposition is complete. The mixture is allowed to stand until the alumina and sulphate of lime have subsided. The supernatant water holding the sulphate of potash