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Part I—The Nature of Anomalous Flow The flow of many solutions, most of them colloidal, is now known to be anomalous since they do not obey the linear Poiseuille relation connecting volume efflux with pressure applied. Under small pressure heads, the rate is disproportinately small compared with that under higher pressures so that the "viscosity coefficient" calculated from these rates is not a constant but becomes larger as the rate of flow decreases. This was first established by Hess in 1906; although in 1903 it had been found that the oscillating disc method gave "viscosities" for colloidal systems which varied with the amplitude of the oscillation. In 1913 Hatschek found similar effects in many colloidal systems using the Couette co-axial cylinder viscometer. Most lyophilic colloids show anomaly to a greater or less extent; and for these systems particularly viscosity has always been regarded as a characteristic property and used as an indicator of lyotropic changes. It is because viscosity is a property so suitable for investigation of lyophilic colloids that it is of importance that more should be known of the relation between viscosities and particle dimensions; of the nature of anomalous flow and its origin. Anomaly is obvious as deviations from a linear relation between pressure head and volume efflux, but its detection in this manner throws no light upon its nature or its origin. Hagenbach's derivation of the so-called Poiseuille equation first showed that this depends upon a parabolic velocity distribution across the flowing liquid, as postulated by Newton. If the equation fails, the velocity distribution is not parabolic. Porter proposed a formula for anomalous flow upon the assumption that the "viscosity coefficient" varied with rate of shear and that the velocity distribution has an exponent less than 2. From the observed volume efflux under known pressures, its value was then to be calculated. The anomaly is, however, too complex to be dealt with in this manner.

The energy of activation found for the benzalazine decomposition is somewhat higher than those hitherto recorded for the decompositions of azo-compounds. The difference between the azine- and azo-decompositions can only be appreciated, however, on comparing the decomposition of benzalazine with that of its aromatic azo-analogue, i . e ., ω-azotoluene. According to Thiele,* when the latter substance is heated in vacuo , gas liberation begins at 15°-180° C. C 6 H 5 . CH 2 ─ N = N ─ CH 2 . C 6 H 5 = N 2 + C 6 H 5 . CH 2 . CH 2 . C 6 H 5 . This reaction is analogous to the benzalazine decomposition (measured at 318°- 180° C), C 6 H 5 . CH = N ─ N = CH. C 6 H 5 = N 2 + C 6 H 5 . CH = CH. C 6 H 5 , and resembles the aliphatic azo-decompositions investigated by Rams-perger over the temperature range 250° - 350° C, though occurring at a lower temperature than these.

Ramsperger has investigated the kinetics of the thermal decomposition of a number of aliphatic azo-compounds at temperatures between 250° and 330° C. The principal reaction is in each instance of the type R. CH - N = N - CH . R ' = N 2 + x . R . CH . CH . R + x . R ' . CH . CH . R ' + (1 - 2 x ) . R . CH . CH . R ' . For a symmetrical azo-compound (R = R ' ), x = 0. When heated to about 300° C., benzalazine undergoes an analogous decomposition, mainly to nitrogen and stilbene ; but the liberation of nitrogen from benzalazine involves the rupture of two double bonds, instead of two single bonds as in the azo-compounds C 6 H 5 CH = N - N = CHC 6 H 5 = N 2 + C 6 H 5 CH = CHC 6 H 5 . A study of the kinetics of the benzalazine decomposition therefore offers the opportunity for a comparison of the breakage of the single and double carbon-nitrogen bonds. We find that the reaction can be followed manometrically at temperatures between 315° and 360° C. These temperatures lie above the boiling-point of benzalazine and stilbene (b. p. 306°), and therefore the reaction proceeds with increase of pressure over a wide range of initial concentrations.

Both Acton and Collingwood believed that until the later nineteenth century historical studies were in a position similar to that of the natural sciences before Galileo. In fact, this analogy between a nineteenth-century "historical revolution" and the seventeenth-century "scientific revolution" extends beyond the development of the discipline itself to the criteria by which it still tends to judge its own past. Just as physics and astronomy before Galileo and Newton were once regarded by historians of science as the superstitions of an unenlightened age, so today the achievements of the comparable "pre-scientific" period of history-writing, unless manifesting some literary or philosophical merit, tend to suffer from a similar disdain. Modern professional historians, it is true, have little alternative but to apply the exacting standards and sophisticated criticism of today's study to their predecessors from whatever period who come before them as possible sources of testimony or pieces of evidence. Weighed in this balance, from Ranke's appendix to the History of the Latin arnd Teutonic Nations onward, the historical work of the sixteenth, seventeenth, and eighteenth centuries has, not surprisingly, been found wanting. But the historians of historical thought, who might have been expected to consider the historiographical past more sympathetically in its proper context of changing assumptions and values, have been no less anachronistic in their judgments. Looking backward from the same post-nineteenth-century vantage point, they have tended to evaluate periods and writers principally by the criterion of how much each has contributed to the evolution of the modern discipline of history. In the first great survey by Eduard Fueter and in the latest by Peter Burke, the Renaissance is sifted for early signs of the attitudes and techniques which have since come to dominate historical work.' Other