Rectifying columns are usually coated with insulating materials to prevent heat loss. It is generally supposed that the heat loss through the column wall lowers the rectifying efficiency; the author, however, has found no paper yet concerning the quantitative relation between the heat loss and the rectifying efficiency.
In the present paper the author wishes to explain a graphical method for solving the number of theoretical plates (N.T.P.) based on McCabe-Thiele's method with some modification due to heat loss. The relation between x_n and y_n+1 is represented by a straight line passing through a definite point, the slope of which, however, changes successively at every plate; so that for the entire enrichment column there are to be a number of operating lines through a definite point. The same is the case with the stripping column.
The author has proposed a relatively simple graphical method of representing these operating lines, Using these operating lines and the equilibrium curve, N.T.P. is obtained by McCabeThiele's method.
Finally, comparing the N.T.P. thus obtained with that of the adiabatic column under the same condition, the effect of heat loss may be represented by plate efficiency.
In laboratory stills, the rectifying column is usually electrically heated to prevent natural cooling. When strongly heated, partial evaporation will take place in the colunm; and the same principle of graphical solution will be applied to this case, too.

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Limiting velocities of counter current gas and liquid flow in empty columns were measured using steel pipes. Flooding points were determined from gas-velocity-pressure-drop plots on logarithmic papers. Even above the flooding point, when bubbling occurred at the top, accompanied by larger pressure drop and liquid head, the liquid easily passed down through the column in spite of larger gas velocity. This velocity range was tentatively named Over-Flooding.
Results were summarized as follows;
For the Flooding point, similar relation to that of Sherwood et al. for packed columns was derived.
For the Over-flooding range, cerrelation involving (d/H)^1/3 proved successful.
Previous Holmes' data were almost successfully applied to the author's curve here presented.
Frome the above stated it is considered that the results suggest something fundamental of the flooding phenomenon.

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The hold-up on the plate and the pressure drop through the plate under various conditions were measured, and it was found that the hold-up was not constant for either the rates of liquid or those of vapor.
On the basis of this experimental results the mechanism of pressure-drop through the perforated plate was discussed and the following results wer obtained;
1) The amount of hold-up increases with the increase of the overflow rate and decreases with the increase of the gas or vapor rate.
2) The relation between Δp_w and H is given by the equation
3) The foaming density is shown by the following equation.
4) The pressure drop through the dry plate is shown by the equation
Although the coefficient of discharge, c, varies with the changes of the diameter of the bole and the thickness of the plate, it is independent of the pitch of the hole.
5) The total pressure drop through the plate is given by the following equation.

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In one of the previous papers on vapor-liquid equilibrium relations, a correlation was presented between n and α₁/α₀ (Fig. 1). In the present paper some correlations are offered for predicting α_n and n from α₁ and α₀. The correlation of Eq. (1) (Fig. 2) is found empirically, while the correlations of Eq. (10) (Fig. 4) and Eq. (13) (Fig. 5) are derived theoretically with the aid of X-Γ curve (Fig. 3). These relations are shown to give fairly good estimation, and to make it possible to test experimental data and to predict vapor-liquid equilibria of binary systems from boiling point or total pressure more easily and more accurately. It will be noted, however, that the empirical correlation of Eq. (1) shows considerable discrepancies for those azeotropic systems in which the values of α₁/α₀ are very small.

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