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743 C H E M I S T R Y tion corresponding to the hydrogen liberated, and in excess particularly because of the many difficulties in the way of that observed Avhen no hydrogen is liberated. The of arriving at really comparable values. In the case of production of butyric and caproic acids, of amylic alcohol, gases, as the molecules are widely separated, they may be and also that of fat, can only be explained on the assump- regarded as independent entities and outside the range of tion that while one set of molecules undergoes reduction intermolecular attractions. But this is not the case with another set undergoes oxidation. The separation of oxygen liquids or solids, and our knowledge of physical properties as such has not yet been observed to take place during relates mainly to the liquid state. The molecules in fermentation, but if hydrogen be evolved as the result liquids are undoubtedly held together with a degree of of “ excessive ” oxidation, it would seem to follow that firmness—and to an extent—which varies from series to oxygen should be evolved if reduction took place to an series, and even within series, so that although in the case extreme extent.1 It is conceivable, and indeed probable, of liquids composed of molecules which are easily separable, that the oxygen evolved from plants in sunlight owes its it may be possible to make comparisons at corresponding origin to an effect of this kind, and that it may be con- temperatures at which the character of interrelationship of nected with the reduction of chlorophyll previously referred the molecules is of the same order, or nearly so, for all the to as a necessary step in the reduction of carbon dioxide. substances, in other instances this is impossible. Acetic In other words, the chlorophyll acts, in a measure, as a acid may be cited as an extreme case. As the vapour of polarizable electrode or catalyst, against which hydrogen this compound, even at temperatures considerably above is delivered, and at which the dioxide suffers reduction, its boiling-point, is not composed of the fundamental being one term in a complex circuit in which hydrolytic molecules represented by the formula C2H402, but mainly change is proceeding. It is a noteworthy fact that a consists of complex molecules formed by their union, it is tendency to form fat—the most highly -reduced normal impossible to contrast acetic acid properly with compounds product of vital metabolism—is particularly noticeable in which are readily reduced to the unimolecular form. the case of animals, and that oxidative changes occur in Whenever possible the boiling-point has usually been these to a far greater extent than in plants. selected as the temperature at which there is likely to be It is commonly supposed that interactions such as occur the closest approach to uniformity of intermolecular conin animals and plants are not to be regarded as mere ditions, but it is clear that this is by no means always chemical changes, but that they take place within the case. Thorpe and Rodger, who have very carefully f vital™ ° ^ie Prot°plasm> and in subjection to its influence. studied the relationship between the viscosity of liquids and processes. ^ 18 possible to accept this interpretation, and their chemical nature (Phil. Trans. 1894, p. 397), have yet to regard such processes as cases of chemical shown that “ temperatures of equal slope ”—i.e., those at interchange pure and simple. The formation of starch and which drjjdt is the same for different liquids—tend to of fat may be taken as examples. It is impossible at pre- reveal much more definite relations between the values of sent to explain under what conditions and precisely how the viscosity co-efficients (r)) and the chemical nature of these are formed, and yet they are so easily formed that it is substances than can be deduced from observations made at probable that they are produced in a comparatively simple the boiling-point. manner. The formation of starch from glucose is a process At one time there was a strong tendency to believe in in which a large number of molecules of the latter become physical constants, and to regard the molecular values as associated, and one in which, doubtless, molecule must be the sums of certain fixed atomic values. As ■“ presented ” to molecule in some very definite manner. the area of discussion has been widened, however, Variation It may well be that glucose does not exist in an ordinary and not only compounds of relatively simple conaqueous solution in the proper form to undergo considera- stitution, but also those more complex in struction. There are at least two isodynamic forms of glucose : ture have been studied, the conviction has gained ground that the “ atomic ” values are subject to considerable variaCH2(OH).CH(OH).CH(OH).CH(OH).CH(OH).(COH) tion. Such variations almost always occur in cases in €H2(OH).CH(OH).CH.CH(OH).CH(OH).CH(OH). which they are to be expected on chemical grounds. Thus -O / the nearest approach to constancy is observed in the parafOf these the second appears to be a relatively inert form, finoid hydrocarbons, which are remarkable on account of and this perhaps is the dominant, if not the only form, the simplicity and uniformity of their chemical behaviour existing in a dilute solution. It is conceivable that such as well as on account of their inertness. Ethenoid hydroa molecule might enter into loose combination with a carbons differ entirely in many of their properties from protoplasmic molecule in such a way as to cause its con- the parafiinoids, the ethenoid linkage exercising a peculiar version, so to speak, into the more active aldehydic form, physical effect; the extent to which variation occurs within in consequence of the OH groups becoming attached to the series, however, cannot be judged of, as the material the protoplasm. The aldehydic group would then be in a available for discussion is altogether insufficient. Benposition to operate freely. It is also possible that in the zenoid hydrocarbons exhibit an altogether peculiar and case of a compound such as glucose the configuration is variable behaviour. Hot only are the peculiarities of the hydrocarbons reprosuch that the OH groups mutually interfere, and, as it were, promote a policy of vacillation, and that on one set duced in their derivatives, but in many cases other becoming neutralized by attachment to the protoplasm peculiarities become apparent which are clearly traceable another set becomes free to act uniformly, so that their to the influence exerted by the radicle introduced into the activity can be manifested in a direction before impossible. hydrocarbon complex. There is reason to suppose that in the case of paraffinoid compounds the hydrocarbon radicle has a practically constant influence, and that the variations Physical Properties. That physical and chemical properties are strictly observed in ascending the series may be referred to differcorrelative there is not the slightest doubt, but the exact ences in the influence exerted by its associates. In other nature of the relationship is far from understood, more series probably both radicles are variants. In ethenoid compounds, in which two of the carbon atoms may be 1 It has recently been stated by Pakes and Jollyman {Trans. Chem. regarded as united by two affinities of each, but in such a Soc. 1901, 322). that a little oxygen is contained in the gases produced way that the full force of each affinity is far from being by B. pyocyaneus when grown anaerobically. exerted, the affinities are deflected from the mean positions