An apparatus and a method for immunological labeling of thin tissue sections are disclosed. The pendent phenyl group can provide an easily sulfonable site that may be sulfonated under mild conditions, providing the ability to precisely control the sulfonic acid content of the SPAE. Alternatively, the valve stem can be directly engaged for rotational reciprocal movement within the valve housing. This device may include: a first assembly for supplying a displaced volume measurement, comparing this measurement to a desired value and generating an indication of the difference between the measured volume and the desired value; and a second assembly, responding to the first assembly, for delivering information relating to the indication.