PART. V. The preliminary research on the occurrence of zymase and carboxylase in Rhizopus species. PART. VI. The veriflcation of the occurrence of zymase in Rhizopus species. PART. VII. On the formation of ethyl alcohol from acetic acid by acetone-Rhizopus (Rhizopus treated by acetone.) PART. VIII. On the formation of ethyl alcohol from malic acid by Rhizopus species. PART. IX. On the formation of ethyl alcohol from malic acid by ace'one-Rhizopus

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(1) The reduction potential of nicotinic acid was measured with the dropping mercury cathode and the polarograph.
(2) Two stages of the reduction process were observed.
(3) For the first stage of reduction, observed R-P. was compared with the theoretical value calculated by the following formula at 15°C.,
π=-0.05713/2logk'/?H^.?²C_C5H4N•COOH in which by taking the R. P. of 0.01 mol nicotinic acid in (0.01n HCl+0.1n KCl) solution, i.e. -0.984V as a standard, we have
log k=28.33
In an acidic as well as in a neutral salt solution, the observed R. P. showed satisfactory concordance with the calculated values, and thus the first stage has been concluded to be the reduction of the carbonyl group of nicotinic acid to aldehyde.
(4) The second stage of reduction is considered to be the reduction of pyridine ring of nicotinic acid, by comparison with the R. P. of pyridine in our preceding paper.
(5) The reduction of nicotinic acid in an excess of alkali, does not take place, owing, perhaps, to the desorption of negatively charged nicotinic acid ions to the polarised mercury cathode. R. P. in a sodium acetate or sodium bicarbonate solution was about 0.02V more negative than the calculated value.
(6) Maximum of current voltage curve was observed in sodium bicar-bonate solution, in which the potential of maximum current intensity was almost independent of the concentration of nicotinic acid.
(7) The reduction potential of benzoic acid was studied for the sake of comparison, with the result that in hydrochloric acid, no reduction but only the deposition of hydrogen ion has been seen, while a potassium chloride solution the R. P. is over 0.240V negative than that of nicotinic acid. Thus the group effect of a carbonyl group is considered to be more effective than a benzene ring.
(8) The decisive conclusion as to the reduction process has been left out for the time, when the isolation of the reduction product, now under investigation, would be completed.

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(1) The polarographic method has been applied as the qualitative as well as the quantitative microanalysis on the studies of reducible compounds in the fermentation products, “such as sake” (japanese rice wine), “ushoyu”(soya bean sauce), wine, beer and commercial alcohol.
(2) For the “sake, ” we have found five reducible compounds, which are distinguishable by this method, from the reduction potentials and the saturation curves of polarograms. They are Reduction potential in 0.1 A NH₄Cl from N calomel electrode
Compound I -0.22 V
Compound II .-0.40 V
Compound III -0.90 V
Compound I V -1.33 V
Compound V -1.63 V
The reduction potentials of reducible substances possibly present in the sake are measured
Cinnamic aldehyde 0.001% -0.913 V in 0.1 n NH₄Cl
Furfural 0.001% -1.302 V in 0.1 a NH₄Cl Acetaldehyde 0.001% -1.603 V in 0.1 n NH₄Cl
Compound IV and V are found in the distillate (80°-100°C), while compound I and II are observed in the residual solution after distillation; compound III is found in both cases. Thus it is concluded that the compound III corresponds to the aromatic aldehyde, most probably cinnamic aldehyde or benzaldehyde, compound IV to be furfural, compound V to be aliphatic aldehyde, most probably acetaldehyde.
(3) In “shoyu”, compound I, II, III, IV and V are found, in which compound II is much conspicuous than all the other cases.
(4) In wine, five compounds are also found ; but except comp-II, the waves are smaller than in the case of “sake”.
(5) With respect to reducible compounds, beer is much simpler, and comp-111, IV and V only are recognisable, but not comp-I and II.
(6) In the commercial alcohol, reducible substance are also found, although much less in quantity, so it has been suggested, that this method can probably useful as one of the criterion for the purity of alcohol.
(7) Consideration has been given for the quantitative analysis of acet-aldehyde.
(8) Thus the polarographic method has proved to be of much applicable for the studies of the fermentation products, although this method is by no means the decisive identification of the reducible substances.

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The above results are summarized in the following scheme:-

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