SACCHARI3IFTRY. A generic term for certain operations under taken with the view of ascertaining the quantity of sugar present in any matter that may contain it.
Sacchasimetry is frequently performed upon solutions which are known to contain cane (ordinary) sugar only, the object being merely to ascertain the amount present. In such a case it Is only necessary to take the specific gravity of the liquid by a hydrometer, and then refer to a previously prepared table of densities and per-centagee. If Baumes hydrometer be used, the degrees of specific gravity marked on its stem indicate the following centesimal proportions of sugar: 1' Baumi corresponds to sp. gr. 1'007; 10' to sp. gr. 1'070; 20° to 1.152; 30 to 1.245 ; 35' to 1199'3 &e.
If a liquid contain other substances besides cane-sugar, the test of specific gravity is of no value. In such a case advantage may be taken of the fact that syrup causes right-handed twisting in a ray of plane polarized light, to an extent exactly proportionate to the amount of sugar in solution. The saccharine fluid is placed in a long tube having opaque sides and transparent ends ; and a ray of homogeneous light, polarized by reflection from a black glass mirror 1Pot..taizavtos OF Lions], is sent through the liquid and optically examined by a plate of tourmaline, Nicol's prism, or other polarizing eye-piece. Attached to the eye-piece is a short arm which traverses a circle divided into degrees. The eye-piece and arm are previously so adjusted that when the ray is no longer visible the arm points to the zero of the scale of degrees. The saccharine solution, however, so twists the ray as to again render it visible ; and the number of degrees which the eye piece has to be rotated before the ray is once more invisible is exactly proportionate to the strength of the solution. The value of the degrees having been ascertained by direct experiment and the results tabulated, a reference to the table at once indicates the percentage of sugar in the liquid under examination. Grape-sugar also possesses the property of but less powerfully than cane-sugar ; moreover the former variety does not, like cane-sugar, suffer inversion of the direction of rotation on the addition of hydrochloric acid to its solution : an operation that furnishes data for ascertaining the amounts of cane and of grape-sugar, or of crystallizable and non-crptallisable sugar, present in a mixture. In using the polariscopo-saccharometer,
it is convenient to use tubes of uniform size, and always to operate at the same temperature.
Cane-sugar is readily converted into grape-sugar by boiling for two or three hours with dilute solution of sulphuric acid, and the grape sugar may then be estimated by the depth of colour which results on boiling it with solutions of caustic) soda or potash ; comparison being made with standard coloured solutions prepared from known quantities of grape-sugar. The quantity of grape-sugar, and indirectly of cane sugar, may also be determined by the amount of its solution which is required to be added to a given volume of a standard alkaline solu tion of tartrate of copper and potash, before complete precipitation of the copper (as suboxide, is effected. The standard solution referred to is known as Fehling's, and is thus prepared :-1 ounce of crystallised sulphate of copper, 3 ounces of bitartate of potash, 16 ounces of pure carbonate of potash, and 14 or 16 ounces of a solu tion of caustic soda of sp. gr. 1.12 are mixed together, and water added until the whole measures 15,160 grains : 200 measures of this solution contain an amount of copper that is perfectly precipitated by one grain of grape-sugar In using Fehling's solution, a tem perature approaching the boiling point should be maintained, and the saccharine liquid should be slowly added from a graduated burette. By either of the above processes the separate amounts of cane and of grape-sugar in a mixture of the two may be ascertained by two operations; ouo performed before boiling with dilute acid and the other after : the quantity first indicated will be the grape-sugar, and that, being subtracted from the numbers obtained in the second experi ment, gives the proportion of cane-sugar. One-eighteenth of the latter number must, however, be deducted; the equivalent of grape-sugar being higher by that amount than cane-sugar.