578 



SCIENCE 



[N. S. Vol. XLIV. No. 1138 



obtain a balance is decreased, and hence the 

 apparent "capacity" of tbe cell is increased; 

 (4) the higher the apparent " capacity " of the 

 cell, the smaller the change of resistance with 

 change in frequency; (5) solutions of differ- 

 ent salts having about the same resistance in 

 the same cell give approximately the same 

 change in resistance with change in frequency 

 from 600 to 1,000 cycles. 



By comparing the resistances of iV/10 and 

 N/20 NaCl in two cells, one of which had 

 bright and the other platinized electrodes 1 

 inch in diameter, it was seen that the ratio 

 for the cell with bright electrodes was much 

 lower than that for the cell with platinized 

 electrodes, but as the frequency was increased 

 the ratio for the cell with bright electrodes 

 approaches that for the cell with platinized 

 electrodes. Extrapolating the resistance for 

 the cell with bright electrodes to infinite fre- 

 quency, the ratio was found to differ by only 

 0.01 per cent, from that given by the platin- 

 ized electrodes. It is thus shown that the true 

 electrical resistance of solutions can be meas- 

 ured or calculated in cells with bright plati- 

 num electrodes only at infinite frequency. 



Saturation of bright and platinized elec- 

 trodes with hydrogen produces no appreciable 

 change in the " capacity " of the cell at 60 

 cycles. This and much other evidence seems 

 to show that the " capacity " does not arise 

 from a neutral gas layer deposited on the elec- 

 trodes and acting as an air condenser. It is 

 probably due to a " double layer " of the elec- 

 trolyte and the " contact potential " arising 

 from changes of concentration resulting from 

 electrolysis and to the reverse electromotive 

 force coming from the deposition of ions on 

 the electrodes. 



The inductance necessary to balance the 

 " capacity " of the cell is nearly but not quite 

 inversely proportional to the square of the 

 frequency. As this relation holds true for a 

 " leaky " condenser the cell seems to act as a 

 simple condenser with a " leak." 



As the frequency of the alternating current 

 is increased the change in resistance of a given 

 solution in a given cell, and also the induc- 

 tance necessary to balance the capacity of the 



cell, are decreased, and both approach zero at 

 infinite frequency. The ratio of the difference 

 in the inductance in millihenries to the dif- 

 ference in the resistance in ohms between 600 

 and 1,000 cycles has a constant value of about 

 2.00. 



Mr. Henry P. Hastings is continuing the 

 work by making measurements of resistance, 

 capacity and inductance at much wider range 

 of frequency, namely, 60, 250, 500, 750, 1,000, 

 1,500, 2,000 and 3,000 cycles. He has con- 

 firmed the fact that a change in frequency 

 produces a change in inductance necessary to 

 balance the cell capacity which corresponds 

 fairly closely to the equation KL = 1/Cw 2 . 

 At lower frequencies he observes easily a third 

 harmonic produced by the cell. Mr. Hastings 

 has also confirmed our work by extrapolating 

 the resistances of solutions in cells with 

 bright electrodes to infinite frequency and 

 showing that they approach the values given 

 by the same solutions in cells with platinized 

 electrodes. 



He has also found that the ratio of the 

 change of resistance which is sometimes 5 per 

 cent, of the resistance, to the change of in- 

 ductance produced when the frequency is 

 changed is approximately constant. 



W. A. Taylor, 

 S. F. Acree 



University op Wisconsin 



on the regularity of blooming in the 

 cotton plant 



In 1915 the writer carried on some experi- 

 ments on the water requirement of cotton, in 

 connection with which the blooming records of 

 a number of plants were kept. In looking over 

 these records, there appears to be a sort of reg- 

 ularity in which the blooms opened and two 

 of these records which showed the greater 

 regularity are herein given. 



To those unacquainted with the habit of 

 growth of the cotton plant it will be well to 

 first call attention to the different kinds of 

 branches as shown on the accompanying dia- 

 grams. On the one of plant No. XIV., those 

 branches numbered one and two are known as 

 vegetative branches; these occur on all plants 

 of this species so spaced as to have freedom in 



