fluid volume this indication of fluid volume verifies that a correct volume of reaction mixture was used further the vent 30 can be used as a viewing chamber use of and the gravity flow induction of a reaction in the apparatus of fig2 is then as described above in the embodiment of fig1 the embodiment of fig2 is configured for latex agglutination reactions for example fig3 provides an embodiment of the present invention which operates in a manner similar to that of the foregoing embodiments but provides an angled channel segment 36 which delivers reaction products into the viewing chamber 38 the angled channel segment 36 provides an isolated area in which to place a magnet for magnetic capture of reaction products procedures for magnetic capture are known in the art and generally described in u s patent application ser no 07 189 983 for a 34 capillary flow device and double capture assay method for use in same 34 and assigned to the assignee of the present invention now abandoned hence the fig3 embodiment of the present invention is suited for carrying out antigen antibody specific binding assays for example of drugs hormones and etc further the apparatus in fig3 has a supporting rib 34 around its outer periphery for structural support as shown in cross section in fig3 a rib 34 protrudes from the plate member 39 a greater distance i e has a greater depth than do channel 37 and vent 35 this rib 34 may be included in other embodiments as desired also fig3 b illustrates the protrusion depth configuration of the entry chamber 33 relative to.