The investigations described in previous papers on this subject have related mainly to the paraffin hydrocarbons (Townend and Mandlekar 1933
a,b
; Townend, Cohen and Mandlekar 1934; Townend and Chamberlain 1936, 1937). It has been found that mixtures with air of the members containing three or more carbon atoms, while not spontaneously ignitible at low pressures below about 500° C., give rise abruptly to ignition at higher pressures in a temperature range between about 310 and 370° C., where normally only cool flames are initiated; and although neither methane- nor ethane-air mixtures appear to develop cool flames, the latter are ultimately ignitible in a lower temperature system which is less complex than that characteristic of the higher paraffins. Moreover, it is now recognized that “knock” in internal combustion engines arises in circumstances responsible for pronounced chemical reactivity in the unburnt explosive medium characteristic of that occurring in the lower temperature range (cf. Egerton and Ubbelohde 1935; Ubbelohde 1935), and the investigations referred to have indicated that the “knock-ratings” of the paraffins when used as fuels in such engines are related to the pressures requisite for the occurrence of spontaneous ignition in this range within an appropriate short time lag (Townend and Chamberlain 1936, p. 104, cf. Prettre 1936
a
and
b
)
Effect of Temperature, Pressure, and Chemical Composition on the Electrical Conductivity of Schist: Implications for Electrical Structures under the Tibetan Plateau