222 



SCIENCE 



[N. S. Vol. XXVIII. No. 711 



constant volume, multiplied by the ratio of the' 

 specific heats less than one, is equal to 2K where 

 K is the gas constant. 

 Borne Relations at the Critical Temperature: J. 



E. MiULS. 



It was shown that if the density of a liquid be 

 plotted against the temperature the line drawn 

 through the density where it varies linearly with 

 the temperature will, if prolonged, cut oflf on 

 the ordinate line at the absolute zero just twice 

 the distance that it cut off on the ordinate line 

 at the critical temperature, and this line in- 

 tersects the temperature axis at a point equal 

 to twice the critical temperature. Jloreover, the 

 line of mean density of liquid and saturated vapor 

 discovered by Cailletet and Mathias likewise 

 meets the temperature axis at the same point 

 (twice the critical temperature). The critical 

 density is therefore one fourth of the density of 

 the liquid at absolute zero. 

 The Relation of the Rate of Settling to the Size 



of Particles in Suspension: E. E. Fkee. 



Most investigators of sedimentation phenomena 

 have worked with very fine powders where the 

 factors effecting the rate of fall are exceedingly 

 complex. This paper describes an attempt to 

 study the much simpler case of the fall of rela- 

 tively coarse particles. Quartz sand of various 

 sizes was dropped through distilled water in a 

 long tube and the velocity of fall measured be- 

 tween points a meter apart. It is shown on 

 theoretical grounds that for spherical particles 

 the relation of velocity and size of particle is 

 given by the equation V- = Kr where K is a' 

 constant. Taking the value of i as found for 

 the coarsest particles (which are least likely to 

 be subject to disturbing influences), the theo- 

 retical parabola is plotted and it is shown that 

 the points for powders less than .25 mm. in 

 diameter lie far above the curve. That is, the 

 finer powders fall more slowly than would 

 theoretically be expected. This is probably due 

 in part to the action of secondary forces and in 

 part to the fact that finer grains are more 

 angular and do not approach the spherical form 

 so nearly as do the coarser. With the finest 

 powders floeculation comes into play and again 

 increases the rate of fall. 

 The Aluminum Cell for preventing Underground 



Electrolysis: F. E. Galiagheb. 



After a brief discussion on prevention of un- 

 derground electrolysis, experiments with a cell 

 containing electrodes of aluminum and lead in a 



sodium acid phosphate solution were described. 

 The length of time a " formed " aluminum elec- 

 trode is held cathode determines the extent to 

 which a film decays, and therefore the time re- 

 quired to build up a high resistance when such 

 an electrode is again made anode. The effective- 

 ness of an aluminum anode in checking current 

 is less at low impressed voltage. Under con- 

 tinued direct current action both the lead anode 

 and aluminum cathode are attacked in sodium 

 acid phosphate solution. Carbon instead of lead 

 in phosphoric acid solution would prove more 

 seiTiceable. 



The Specifio Heat and the Latent Heat of 

 Vaporization of Silicon Tetrabromide : L. 

 Kahienbeeg and E. H. Zobel. 

 The silicon tetrabromide was prepared by pass- 

 ing bromine over heated metallic silicon. The 

 product was freed from excess of bromine by 

 fractional distillation, treatment with metallic 

 mercury, and finally redistilling. The boiling 

 point of the purified product was 148°. 7 at 736 

 mm. pressure. The specific heat between the 

 temperatures of 24° and 144° was found to be 

 0.10055, and the latent heat of vaporization was 

 found to be 28.86. The method for determining 

 the specific heat was that employed by Berthelot, 

 and the method of Kahlenberg was used in 

 making the determinations of the latent heat of 

 vaporization. The figures obtained are the mean 

 of several determinations that gave closely agree- 

 ing results. 



Equilibrium in the System Silver Chloride ami 

 Pyridine: Louis Kahleistbebq and Walteb J. 



WiTTICH. 



There are two distinct crystalline compounds 

 of silver chloride and pyridine, namely, 

 AgC1.2C5HsN and AgCLCsHtN; these have hitherto 

 been unknown. The former compound is stable 

 between — 56° and — 22° C. It was obtained in 

 minute crystals that are very unstable at tem- 

 peratures above — 22° C. AgCl.CjHBN is stable 

 between — 20° and — 1° C. The salt forms 

 small needlelike crystals which are more stable 

 than AgCl.CcHsN. From —1° to 110° C. the 

 solubility of AgCl in pyridine decreases rapidly 

 as the temperature rises. The entire equilibrium 

 curve of the system silver nitrate and pyridine 

 has been established from the freezing-point of 

 pyridine up to 110° C. 



The Validity of Faraday's Law at Low Tempera- 

 tures: Wendell G. Wilcox. 

 The experiments were made on silver nitrate 



