Abstract: In the present paper, as a second part of the previous paper published in this journal (No.1, 16-23, 1958), the authors made further experimental studies on single slots of different shapes and dimensions to correlate slot opening with air flow rate. Considering the vapor velocity in the annular space between the riser and the bubble cap in operation, which had been neglected in the single slot studies, the authors presented a new approach to evaluate the slot opening, which was tested experimentally. (1) For single slot studies, experimental conditions were extended as follows. Slot dimensions, rectangular slots, 6=2.27-25.28mm; triangular slots, B/H=0.255-1.40; trapezoidal slots, (B2-B1)/H=0.072 -0.796. Air flow rates. Vs≤357×102litres/hr. Immersed depth. 30mm. The results shows that the value of the discharge coefficient u in the Rogers-Thiele formula is not a constant but a function of Reynolds number as well as slot dimensions. For definite slot dimensions, the value of u will be a constant only when the air flow Reynolds number is high. ( 2 ) With the effects of the annular space vapor velocity considered, the authors proposed the following formulas as a modification of those of Rogers and Thiele. Rectangular slots. Triangular slots. Trapezoidal slots. It is apparent that the Rogers-Thiele formulas are only special forms of the above with a= 0.( 3 ) Formula (6) was tested experimentally in a single bubble cap, with the following experimental conditions. Bubble cap shape and dimensions. Circular cap with 40 rectangular slots; Cap I.D., 100mm; Riser O.D., 68mm; Slot width, 4mm; Slot height, 25mm. System. Air-water. Operating conditions. Static immersed depth, 15mm; Air flow rates,V = 22.1-111.0 cubic metres/hr. The results point out that the formulas proposed in the previous paper can be applied to bubble caps at Re≥2600 without appreciable error. The experimental data were compared with the calculated values of slot opening from the Rogers-Thiele formula, the Cross-Ryder formula, the formulas in the previous paper,and formula (6 ) in this paper. It has been found that when Re≥2000, the maximum deviation for formula (6 ) was 3%, while that for the other formulas were 17.5%, 9.2% and 8.5% respectively. After making a theoretical analysis, the authors are of the opinion that the formulas proposed can represent to a certain extent the operating conditions of a bubble cap. Similar results could be anticipated from a bubble cap with triangular or trapezoidal slots, but further experimental studies will be needed.