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must be decolorized with animal charcoal and concentrated by evaporation to a small determinate volume, which can then be placed in the polariscope. By this method, any bile-acids present in the urine pass over into the alcoholic solution finally obtained, and exercise their dextro-rotatory action. Their presence may be detected by evaporating a portion of the solution, dissolving the residue in a little water and mixing with some yeast. In two or three days all the sugar present will be decomposed, so that if, after filtration, the liquor still exhibits dextro-rotatory power this must be attributed to the presence of bile-acids.

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$ 101. The polariscope has also been employed by Neubauer to detect grape-sugar in “chaptalized ” wine. The potato-sugars of commerce invariably contain from 16 to 20 per cent. of imperfectly known substances (amylin of Béchamp), characterized by high dextrorotatory power, and great resistance to fermentation. When the must has been chaptalized, these substances pass over into the wine.

Pure natural wines of moderate age do not contain such substances, and, therefore, when submitted to polariscopic examination in tubes 2 or 2.2 decimetres in length, either exhibit no rotatory power, or at most a rotation to the right through an angle of 0.1 to 0:4 degree. Choice wines from very highly saccharine must, on the other hand, containing lævulose still unfermented, may appear more or less lævo-rotatory. This is the case with wine “chaptalized with cane-sugar.

The following is the mode of examination recommended by Neubauer:

Fifty cubic centimetres of the wine (whether red or white) are placed in a flask with 5 cubic centimetres basic acetate of lead ; some animal charcoal which has been purified by extraction with hydrochloric acid added, and the whole shaken up for a few minutes, and then filtered. The colourless solution is then introduced into the polariscope in a 2 or 2.2 decimetre tube. dextro-rotatory to the extent of 1° or more, it may safely be concluded that the wine has been chaptalized with potatosugar.

If, however, the result appears doubtful, 100 to 200 cubic centimetres of the wine may be concentrated by evaporation to 25 (or 50)

1 Neubauer: Fresenius', Zeitsch. für analyt. Chem. 1876, 188; 1877, 201 ; 1878, 321.

If it appears

cubic centimetres, treated with basic acetate of lead and animal charcoal as before, and the rotation again examined. A rotation of from 1° to 4° at the least will now be obtained if the wine has been chaptalized. When 400 to 500 cubic centimetres of such wines are reduced by evaporation to 50 cubic centimetres, amounts of dextrorotation of from 5° to go are not unfrequently obtained.

If the result of the first examination shows a dextro-rotation of not more than 0:4° to 0.6°, a further investigation may be made by the following method, which is based on the fact that the unfermentable matters accompanying the potato-sugar are, for the most part, soluble in alcohol, and can be precipitated therefrom by the addition of ether -250 to 350 cubic centimetres of the wine are first concentrated till the salts crystallize out. This liquid is decanted, decolorized with animal charcoal, diluted to 50 cubic centimetres, and finally filtered. Almost all pure natural wines treated in this way will exhibit a feeble dextro-rotatory power, which in tubes of 2 or 2.2 decimetres may amount to as much as about 2°. Wines that have been chaptalized, on the other hand, yield deviations of from 4o to 11°.

After this preliminary examination the 50 cubic centimetre solution must be reduced on a water-bath to a syrupy consistency, and alcohol of 90 per cent. added with constant stirring so long as any deposit forms. The mixture is then allowed to stand for several hours, until the liquid is perfectly clear, when it is poured off from the generally tough gelatinous residue. If, however, the precipitate formed is flocculent it must be filtered. The precipitate A, and the alcoholic solution B, so obtained are then treated separately as follows :

The precipitate A is dissolved in cold water, decolorized with animal charcoal, and filtered. The solution must then be diluted to a volume corresponding with the capacity of the polariscope-tube and placed in the polariscope. In all pure wines, the bulk of the dextrorotatory substances will be found in this solution, which may therefore give an angle of rotation of from 0.5o to 1.8°.

The alcoholic solution B is evaporated on the water-bath, till about one-fourth of the alcohol originally added remains. This is then placed in a small flask, and after cooling is mixed with from four to six times its volume of ether and vigorously shaken. If after standing the ether is found to have separated from the more or less thick watery liquid beneath, it can be removed by decanting, or by the help of a separating funnel. The watery solution is then diluted somewhat with water, warmed to expel any ether still remaining, and decolorized

a

with charcoal. The filtrate, which now contains the unfermentable substances in the original potato-sugar, is then examined in a 2 or 22 decimetre tube. If the wine has been chaptalized this filtrate will exhibit dextro-rotation to the extent of from 30 to 11° or more. In pure natural wines of average quality, on the contrary, the filtrate will, in most cases, appear inactive, or may rotate at most from 0.2 to 0.5° to the right. For this optical examination of wines any sensitive polariscope, such as Wild's or Laurent's, may be used. Special polariscopes of simple form (called optical wine-testers) are manufactured for this purpose at the Optical Institute of Dr. Steeg and Reuter, Homburg v. d. Höhe. These instruments are in construc

. tion essentially similar to that described in § 43, Fig. 20.

C. Determination of Milk-Sugar. § 102. Milk-sugar, C12 H22 Ou + H2O, exhibits, in freshly prepared cold solutions, the property known as bi-rotation (see $ 27). The following numbers apply to solutions reduced by heating to constant rotation.

Hesse examined four aqueous solutions in a Wild's polariscope with a 2 decimetre tube, and found :

ad = 2.144°

[a]

:

forc=

C=

2 3 5

+ 53.60°

53.16° 52.300 52-67°

3:19° 5.29° 12.64°

C =

C = 12

= 53°

Thus the specific rotation decreases with increased concentration ; but for solutions of the above strengths [a]] may

be taken as the mean value. Moreover, since for each decrease of c by 1, a shows a constant increase of 1.05°, the concentration of such solutions may be obtained from the subjoined table, in which :

a is the angle of rotation observed in a 2 decimetre tube with

sodium light, c the corresponding amount in grammes of milk-sugar

(C12H22 Ou + H, 0) in 100 cubic centimetres of solution.

a

11

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0.92
1.87
2.82
3.77
4.73
5.68

6.63 7.58 8.54 9:49 10:44 11:39

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10° 11 12°

S

6°

1 Hesse: Liebig's Ann. 176, 93.

In observations made with a Ventzke's saccharimeter, and taking for the specific rotation of milk-sugar the constant value of 53°, whereby it is made to agree with that of anhydrous glucose, the data afforded by $ 99 show that each division of the scale will represent 0:3268 gramme of milk-sugar in 100 cubic centimetres solution, assuming the rotation to have been observed in a 2 decimetre tube. With the French scale the corresponding value is 0.205 gramme.

To Determine the Milk-sugar in Wilk. For this purpose the fat and lævo-rotatory casein must first be removed. Fifty cubic centimetres of milk are placed in a porcelain basin along with 25 cubic centimetres of a moderately strong solution of ordinary acetate of lead, heated to the point of incipient boiling, and afterwards allowed to become perfectly cold. The mixture, together with the coagulum, is then poured into a 100 cubic centimetre flask, and water added to bring it up to the mark. After shaking and filtering, the rotation is observed

. in a 2 decimetre tube, and the result so obtained doubled on account of the solution having been diluted to half its original strength. When the milk exhibits a strong acid reaction, it should first be neutralized with a few drops of soda solution. As the volume of precipitate is considerable, the result will be somewhat too high (see $ 93).

D. Determination of Cinchona Alkaloids.

a

S 103. The specific rotation of the cinchona alkaloids and of their most important salts has been studied in detail by Hesse. The values so determined serve both as a means of testing the purity of other samples, and in determining the composition of mixtures. Oudemans? has also made a number of observations on the same subject.

The rotation constants which have been determined with the greatest accuracy are those of quinine, cinchonidine, conchinine (quinidine), and cinchonine. In each of these four alkaloids the specific rotation varies considerably with the nature of the solvent, and decreases, moreover, with increase of concentration. Hesse has investigated the rotation of solutions containing, according to their respective solvent powers, from 1 to 10 grammes of substance in 100 cubic centimetres of solution, and has found that within these limits the variations are represented by the formula [a] = A - B c. As solvent, alcohol of 97 per cent. by volume was employed for the pure

1 Hesse: Liebig's Ann. 176, 203; 182, 128. 2 Oudemans: Idem., 182, 33.

2

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alkaloids, and for their salts either water, dilute hydrochloric or sulphuric acid of known strength, the latter being added in such quantity that the solutions contained for 1 molecule alkaloid not more than 3 molecules H Cl or H, S04 This was the proportion of acid used also in the solution of the free alkaloids. In calculating the number of cubic centimetres of standard acid to be added to a given weight of alkaloid, Hesse took 316 for the molecular weight of all four bases, being the mean of 308 (C20H1,4 1,04, cinchonine and cinchonidine), and 324 (C20 H 4 N.,02, quinine and quinidine). The error arising from the slight difference from the true molecular weight is trifling.

As the rotatory power of solutions containing alkaloids decreases more or less with a rise of temperature, the solutions must be kept at a constant temperature. Hesse took 15° Cent. as a standard.

The following tabular arrangement shows the constants obtained by Hesse with preparations of the highest possible degree of purity.

The numbers have reference

1. To compounds of the alkaloids having the chemical formulæ respectively assigned to them (water of crystallization included).

2. To the alkaloid contained in these compounds—the latter numbers being calculated from the former.]

(As in previous cases c stands for the number of grammes of active substance in 100 cubic centimetres of solution; and for subsequent reference the formulæ are numbered.)

Quinine (læro-rotatory). Quinine hydrate, C20 H24 N, 02 + 3 H, 0.

Solution in alcohol 97 per cent. by vol. c= 1 to 10. (1)

[a]] (145.2 – 0.657 c). Quinine hydrochloride, C20 H,4 1,02 . H Cl + 2 H2O. Solution in water.

C = 1 to 3.

2

.

-2

m

1 If [a], be the specific rotation of a compound and [a], that of the active group (e.g., alkaloid) contained in it, then putting M and m as the respective molecular weights:

M [a].

[a], The equation which expresses the value of constant for compounds

[a]v A BC must be transformed for active groups into

M
M
M

M
A B

A + B where d' is the amount of essential active substance (alkaloid) in e parts by weight of the compound. (Hesse : Liebig's Ann. 182, 131.)

ע

2

[a]. = (4 3.0)

()

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