SUGAR OF POTATOES.

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in France, Belgium, and Holland , where the large coarse potatoes are used for thispurpose. The raw material must be very cheap there, as well as the labor; for potato •flour or starch, for conversion into sugar, has been imported from the continent intothis country in large quantities, and sold in London at the low price of 10s. per cwt.

The process usually followed by the potato-sugar makers, is to mix 100 gallons ofboiling water with every 112 lbs. of the fecula, and 2 lbs. of the strongest sulphuricacid. This mixture is boiled about 12 hours in a large vat, made of white deal, havingpipes laid along its bottom, which are connected with a high pressure steam-boiler.After being thus saccharified, the acid liquid is neutralized with chalk, filtered, andthen evaporated to the density of about 1300, at the boiling temperature, or exactly1-342, when cooled to 60 J . When syrup of this density is left in repose for some days,it concretes altogether into crystalline tufts, and forms an apparently dry solid, of spe-cific gravity T39. When this is exposed to the heat of 220°, it fuses into a liquidnearly as thin as water; on cooling to 150°, it takes the consistence of honey, and at100° F. it has that of a viscid varnish. It must be left a considerable time at rest be-fore it recovers its granular state. When heated to 270°, it boils briskly, gives off onetenth of its weight of water, and concretes, on cooling, into a bright yellow, brittle, butvery deliquescent mass, like barley sugar. If the syrup be concentrated to a muchgreater density than T340, as to 1-362, or if it be left faintly acidulous, in either caseit will not granulate, but will remain either a viscid magma or become a concrete mass,which may indeed be pulverized, though it is so deliquescent as to be unfit for theadulteration of raw sugar. The Hull juice is in this predicament, and is therefore, inmy opinion, hardly amenable to the new sugar law, as it can not by any means beworked up into even the semblance of sugar.

Good Muscovado sugar, from Jamaica , fuses only when heated to 280°, but it turnsimmediately dark brown, from the disengagement of some of its carbon, at that tem-perature, and becomes, in fact, the substances called “ caramel” by the French , whichis used for coloring brandies, white wines, and liqueurs.

Thus we see that starch or grape-sugar is well distinguished from cane-sugar, by itsfusibility, at a moderate heat, and its inalterability at a pretty high heat. Its sweet-ening power is only two fifths of that of ordinary sugar. A good criterion of incom-pletely formed starch-sugar is, its resisting the action of sulphuric acid, while perfectlysaccharified starch or cane-sugar is readily decomposed by it. If, to a strong solutionof imperfectly saccharified grape-sugar, nearly boiling hot, one drop of strong sulphuricacid be let fall, no perceptible change will ensue, but if the acid be dropped into solu-tions of either of the other two sugars, black carbonaceous particles will make theirappearance.

The article which was lately detained by the Excise , for the high duties, at Hull, isnot affected by sulphuric acid, like the solutions of cane-sugar, and of the well-madepotato-sugar of London ; and for this reason I gave my opinion in favor of admittingthe so-called vegetable juice at a moderate ra.te of duty.

I submitted the solid matter, obtained by evaporating the Hull juice, to ultimateanalysis, by peroxide of copper, in a combustion tube, with all the requisite precau-tions, and obtained, in one experiment, 37 per cent, of carbon; and in another 38 percent., when the substance had been dried in an air bath, heated to 275°. The differ-ence to 100, is hydrogen and oxygen, in the proportion to form water. Now this isnearly the constitution of starch. Cane-sugar contains about 5 per cent, more carbon,whereby -it readily evolves this black element, by the action of heat or sulphuric acid.

An ingenious memoir, by Mr. Trommer, upon the. distinguishing criteria of gum,dextrine, grape-sugar, and cane-sugar, has been published in the 39th volume of the“ Annalen der Chemie und Pharmacie.” I have repeated his experiments, and findthem to give correct results, when modified in a certain way. His general plan is toexpose the hydrate of copper to the action, of solutions of the above-mentioned vege-table products. He first renders the solution alkaline, then adds solution of sulphateof copper to it, and either heats the mixture or leaves it for some time in thecold. By pursuing his directions, I encountered contradictory results; but, by thefollowing method, I have secured uniform success,, in applying the criteria, and haveeven arrived at a method of determining, by a direct test, the quantity of sugar indiabetic urine.

I dissolve a weighed portion of sulphate of copper in a measured quantity of water,and make the solution faintly alkaline, as.tested with turmeric paper, by the additionof potash ley, in the cold; for if the mixture be hot, a portion of the disengagedgreen hydrate of copper is converted into black oxide. This mixture being alwaysagitated before applying it, forms the test liquor. If a few drops of it be introducedinto a solution of gum, no change ensues on the hydrate of copper, even at a boilingheat, which shows that a gummate of copper is formed, which resists decomposition :but the cupreous mixture, without the gum, is rapidly blackened at the boiling tem *