Abstract: A process for controlling the nitriding effect of a nitriding bath of a salt melt containing alkali cyanate for the nitridation of iron and iron alloys wherein the nitriding effect of the bath is maintained in a specific range by determining the voltage occurring at an electrode of a solid electrolyte which conducts oxygen ions immersed in the nitriding bath.

Abstract: A standstill heating system for vehicles, especially for motor vehicles with a liquid-cooled internal combustion engine and with a controllable heater circulation equipped with at least one heat-exchanger, through which flows air intended to be heated and to be fed to the passenger space in the warmed-up condition; a line in communication with the liquid jacket of the internal combustion engine is thereby provided which includes a circulating pump and a heater apparatus whereby this line terminates in the heater circulatory system upstream of the control member controlling the quantity of flow through the adjoining heat-exchanger; a closure valve is also arranged in the heater circulatory system upstream of the place where this line terminates which prevents a return flow of the heated-up cooling liquid during standstill heater operation in by-passing relationship to the heat-exchanger.