Abstract: A tapping pipe is provided for a melt vessel having a predetermined melt maximum bath level X.sub.m. The tapping pipe defines a flow passage therethrough which has a discharge zone having flow cross-sections approximately the same as the cross-sections of the flow profile of a free flowing stream of the melt from a melt bath level X.sub.0 between 30% and 70% of the maximum melt bath level X.sub.m. The discharge zone can be provided by a brick defining the discharge zone, together with additional bricks defining a feed zone and a transition zone between the feed zone and the discharge zone. In making a number of replacements of the tapping pipe in a converter, the length of the brick defining the transition zone can be gradually reduced so as to compensate for the wear of the converter lining.

Abstract: In a system for determining the colloid index in a liquid, an amount of the liquid is taken from the body of liquid and passed through a measuring filter under pressure. The respective volumes of liquid which are passed through the measuring filter and the respective periods of time for that purpose are correlated, in a plurality of successive steps, and the change in the respective amounts of liquid or periods of time is used as a measurement for determining the colloid index, or the change in the amount of liquid flowing through the filter with respect to time is continuously detected.