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division, due to the conversion of cane-sugar into

invert-sugar. Then

0.52 × 10

=

1.03 per cent. cane-sugar.1

5.02

Unfermentable Residue.-After fermentation of the 10 per cent. sugar solution and treatment as described above (p. 121), the reading in the 200 mm. tube was 0.10 division, and 25 c.c. reduced 0.032 grm. of Cu.

Reducing Sugars.-Ten c.c. of the 10 per cent. solution of the invert-sugar were diluted to 50 c.c., and 10 c.c. of the diluted solution reduced 0.2759 grm. Cu. The rotation in the 200 mm. tube of the 10 per cent. solution was 5.25 divisions.

The reduced copper, 0.2759 grm., multiplied by 500 gives the amount of copper which would be reduced by 100 grms. of the original invert-sugar, viz., 13795 grms. Cu. But this amount has to be corrected for the amount of copper reduced by the unfermentable residue. Twenty-five c.c. of the half-diluted fermented solution reduced 0.032 grm. Cu. Therefore 0.032 × 80 2.56 grms. Cu. reduced by the unfermentable matter in 100 grms. of the sugar.

=

=

Hence 137.95 - 2·56 135·39 grms. Cu. reduced by the dextrose and levulose in 100 grms. of the invert-sugar.

The observed rotatory power of the 10 per cent. solution in the 200 mm. tube has now to be corrected

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for the rotatory power of the cane-sugar and the unfermentable matter present. 0103 grm. of canesugar were found in 100 c.c. of the solution, and the calculated rotation for this amount in the 200 mm. tube is 0.39 division; the corrected reading found for the unfermentable residue was - 0.2 division in the 200 mm. tube. Hence the rotation due to the cane-sugar is added to, and that of the unfermentable residue is subtracted from, the original reading (- 5.25), leaving a corrected reading 5:44 divisions, which gives on calculation an [a]D - 9'44°.

of

On referring to Table III., it is found that with a reduction of 0.2759 grm. of Cu. the grm. value of dextrose is 1.975, and that of levulose 1814; the simultaneous equations for calculating the percentages of dextrose and levulose in the original invert-sugar then become :

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Analysis of Glucose or Starch Sugar.-The analysis is carried out in the same manner as the analysis of invert-sugar described above, but the determination of the cane-sugar is omitted as this sugar does not occur in sugars prepared from starch. When calculating the reducing sugars present the constant for maltose is substituted for that of levulose.

Thus, in an analysis of a glucose, in which 1.45 per cent. of ash, 0.97 per cent. of albuminoids and 15.70 per cent. of water were obtained, the Cu. reduced by 100 grms. of the glucose was found to be, after due correction, 121.97 grms., and the corrected opticity [a] 41.35. The simultaneous equations for calculating the percentage amounts of dextrose and maltose then become :

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SECTION III.

FERMENTATION.

INTRODUCTION.

THE following studies are divided into two parts— one concerned more especially with the physiological aspect of fermentation, and the other with the morphology and life history of the more important micro-organisms of fermentation and with the special methods employed in their examination; but the division is a somewhat arbitrary one, and many points relating to the first part are of necessity studied in the second.

In the earlier courses of study described in this book it was found necessary to enter into detail regarding much of the experimental work, as there was no text-book covering the whole of the required ground to which the student could be referred for information; but there are several text-books on fermentation available, and in the following studies it is proposed to refer to these whenever possible in order to avoid enlarging the present work unnecessarily. For this reason the space devoted to the study of fermentation may

appear limited when compared to that devoted to other studies, but the student must not be misled by this and underrate the length of time required for his fermentation work, for he will perhaps find it necessary to devote more time to it than to any of his previous studies.

PART I.

The Physiological Aspect of Fermentation.

It is not practicable for a student in the time usually at his disposal to study the physiological aspect of fermentation in the laboratory in anything like a systematic manner, for the subject is a very large one, and experiments connected with it take up much time. The following short course of experiments must therefore be regarded as merely an introduction to the experimental side of the subject. It is expected that the student will have become familiar by means of lectures and books with the modern views of fermentation and the life history of fermentation organisms before commencing the experiments described; following on this, the short course of experimental work will then put him in touch practically with the general bearings of the subject.

Determination of the Amount of Alcohol and Carbon Dioxide produced during the Fermentation of Sugar by Yeast.-Prepare a small, light flask of about 200 c.c. capacity with a perforated rubber

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