SU GAR. —Properties.

887

Per Cent.

0° G. (32° Fahr.),. 65

5° C. (41° Fahr.),. G5’2

10° C. (50° Fahr.),. 65’6

15° G. (59° Fahr.),. 664

20° C. (68° Fahr.),. 67’0

’ 25° C. (77° Fahr.). 68’2

30° C. (86° Fahr.),. 69'8

35° C. (95° Fahr.). 72'4

40° C. (101° Fahr.),. 75'8

45° G. (113° Fahr.),. 79 2

50° C. (122° Fahr.). 827

Sugar, like many other organic bodies of complexconstitution, has the power, even when in solution,of rotating or twisting the plane of a ray of polar-ized light; and the amount or degree of rotationwhich it causes is proportional to the number ofmolecules of sugar acting on the ray. Thus, if wepass a ray of polarized light through 100 millimetresof a solution of pure sugar, containing 10 grams, ofsugar in 100 c.c., that ray will be twisted to theright (hence sugar is called dextro-rotatory) into aplane at an angle of n° to its former one; but if wedouble the length of the column of sugar solution,or double the quantity of sugar, the length remain-ing the same, we double the number of actingmolecules, and so double the rotation. This factobviously furnishes us with a method of estimatingthe amount of sugar in any transparent liquid notcontaining any other optically active substance.

The instruments by which this rotation of theplane of polarization is observed are called polari-scopes or saccharometers, and take three principalforms. The first, or “ Soleil-Duboscq ” instrument,especially as improved by Sciieibler, is a goodinstrument for the use of those who have a keenperception of slight differences of shades of colour,but is quite useless to any one at all colour-blind—for whom, as indeed for most people, the instrumentsknown as the Cornu-Jellet polariscope, or sacchari-meter h peuombres, or Laurent’s modification of it,are to be strongly recommended. Space fails inwhich to describe the construction of these variousinstruments; and their manipulation, so far as itneeds description, will be found under the headEstimation of Sugar.

When heated in solution with dilute acids, or whensubmitted to the action of ferments for a limitedperiod, sugar takes up the elements of water, H 2 0,and splits into two molecules of different glucoses—viz., dextrose, which has a right-handed rotatorypower for polarized light; and lsevulose, which islsevo-rotatory. Both have the same formula —C 6 H 12 0 6 —but differ considerably in their properties,doubtless owing to a different arrangement amongthemselves of the atoms, or groups of ultimateparticles, of which the respective molecules con-sist. Because the lsevulose rotates to the left morestrongly than the dextrose to the right, the mixturerotates to the left, or the rotatory action of theoriginal cane sugar has been inverted; whencethe name “ invert sugar ” commonly applied to thismixture. Long boiling with water gives rise to thesame result to a slight extent; but if both sugar andwater be pure and free from all acids, it is to a

slight extent only. It has been stated that anaqueous solution of sugar, when exposed to light,undergoes inversion, but this is not correct. Inthe absence of ferment germs solutions of sugar willkeep unaltered, not only lor months, but for years.

The inversion of cane sugar is accomplished bydifferent acids with very various degrees of rapidity.Dubruneaut states that one equivalent of sulphuricacid (49 parts) has only half as great a power ofinversion as one of hydrochloric acid (36’5 parts),and at 100° C. (212° Fahr.), -j-j^g-th of tartaricacid causes complete inversion. lie further statesthat if one-half the inversion takes place in theunit of time, in the next unit only one-half as muchsugar is inverted, and in the next one-quarter; or,in other words, the action of the acid is propor-tional to the number of molecules of sugar onwhich it has to act. The time required for a givenamount of inversion is, roughly speaking, in inverseproportion to the quantity of acid, the concentra-tion, &c., remaining the same ; but these statementsare contradicted, as regards their quantitative parts,by more than one respectable authority.

. Weak acids, such as acetic and some other vege-table acids, possess very little power of “inversion”at any temperature short of 100° C.; and accord-ingly when sulphuric or hydrochloric acids areadded to concentrated cane or beet iuice, as is donein Demerara, and of late in France by Marguerite,the natural vegetable acids are displaced and setfree by the stronger mineral acids, which becomeneutralized by the bases with which the formerwere originally combined. The free vegetable acids,though making the liquid very sour, invert but littlesugar at the temperature at which the solutionboils in the vacuum. For a very interesting andimportant paper on the inversion of sugar by acidsconsult A. Behr in Stammer ’s “ Jahres-Bericht iiberdie Untersuchungen und Fortschritte der Zucker-fabrikation ” for the year 1874.

Though sugar is so easily inverted by acids, itwithstands the action of alkalies very perfectly—asolution mixed with caustic potash, soda, or lime,and boiled, even, undergoes no change of colour iffree from glucose; and though, while alkaline, itexhibits diminished rotatory power for polarizedlight, it recovers its original power on being neu-tralized. Sugar, indeed, forms many compoundswith the alkalies and alkaline earths to which for-mulae have been given, though they are so difficultor impossible to prepare in a pure state that theiraccurate composition cannot be said to be in allcases determined. The potassium and sodium com-pounds are made by adding strong alcohol to asolution of sugar and potash, or soda, respectively.They are both gelatinous precipitates, difficult to washwith alcohol, and affording no guarantee of purity.The formulae assigned to them are C 12 H 21 KO n , andC^H^NaOji, which are improbable. The bariumcompound is the one which is most definite in itscharacters; it is easily obtained in a crystalline con-dition by boiling down a solution of sugar mixedwith a large quantity of caustic baryta (or sulphide