172 
IOWA ACADEMY OF SCIENCE 
The accompanying curves are drawn according to the accompanying data. 
Curve 3, fig. 1, plate 1, is the E. M. P. on open circuit and was very steady 
after the first few minutes until about three forty, when it suddenly drops. 
This drop is due to polarization and by looking at data No. 4 we will see that 
there is more hydrogen liberated at this point than the nitric acid was able to 
take up. The curve runs along very smoothly until the last hour, where it 
drops a little and also at this point the nitric acid is practically all gone. The 
recovery curve 2, fig. 1, plate 1, came up very rapidly at first and then slowly rose 
until it reached the starting point, where it was very near the calculated voltage 
of the cell when HNO2 is formed. Curve 1, fig. 1, plate 1, which is the E. M. 
F. curve on running down again, dropped so fast that it was difficult to take 
the E. M. F. readings. It dropped to the level of the E. M. P. when the recov- 
ery curve started and then gradually fell. 
The potential curve (18) fig. 2, plate 1, agrees very well with E. M. F. curve 
if we consider curve (c) which is the internal resistance curve. The P. D. 
falls gradually while the E. M. F. runs along very near the same level. This 
fall is due to the use in the internal resistance. This curve runs along with 
the calculated E. M. F. curve (4) fig. 1, plate 1, until it reaches the point of 
polarization. The drop in the sixth hour is due to the rise in temperature at 
that time, shown by curve (9) fig. 2, plate 4, for de-^dt is negative at this point. 
The current curve (17) fig. 2, plate 2, falls faster than P. D. curve because 
the internal resistance here again enters into the equation. The drop at the 
sixth hour here is the same as in the P. D. curve, as would be expected. 
The internal resistance curve (6) fig. 1, plate 2, rises until the nineteenth 
hour when there is a drop. The resistance that is above the level of curve (7) 
fig. 1, plate 2, which is the recovery curve of the internal resistance, is due to 
polarization. The drop here is due to the fact that hydrogen is not liberated 
so fast 'and the nitric acid can take care of it better. The internal resistance 
falls immediately on recovery which shows very plainly the polarization resis- 
tance.- ^ 
The ’wattage curve (8) fig. 1, plate 4, is a combination of the P. D. curve 
and the current curve and has their respective characteristics. The temperature 
curve (9) fig. 2, plate 4, of battery represents the heat developed within the 
battery and it together with the temperature of room shows the heat radiation. 
The specific gravity curves (11) fig. 2, plate 3, and (12) fig. 2, plate 3, 
resemble the HNO3 curve (13) fig. 1, plate 3, and the zinc curve (16) fig. 1, 
plate 5. The reason for this is the fact that the specific gravity of nitric acid 
is proportional to its per cent. The action through the porous cup changes 
this a little and at the end of the specific gravity curve it rises a little, due to 
the heavier zinc solution coming in. In the outer solution the specific gravity 
raises in proportion to the amount of zinc brought into the solution. 
The hydrogen liberated curve (14) fig. 1, plate 3, and the zinc consumed 
curve (16) fig. 1, plate 5, are the same relative curves as the hydrogen liberated 
is proportional to the zinc consumed. These are also the same d,s the HoSOi 
curve only inverted. 
The zinc consumption curve (21) fig. 2, plate 5, against the wattage repre- 
sents the zinc efficiency and is equal to the H2SO4 curve (20) fig. 2, plate 5, only 
inverted. This is true because the amount of chemical work dohe by the zinc 
and H2SO4 is proportional to the zinc consumed. The wattage, that is watt 
hours in the case, is the electrical work done. The HNO3 decomposed curve 
