216 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



were employed. They .at first sank, but soon came to the 

 surface, and floated about until they were melted. 



Mallet has published a paper on the density of solid mer- 

 cury, the experimental investigation having been conducted 

 with great care. A cylindrical specific-gravity flask was pre- 

 pared of glass, whose capacity at 4 C. was determined botli 

 by direct and indirect calibration to be 59.7311 grams. The 

 freezing mixture used was snow and hydrochloric acid, the 

 temperatures were determined by an alcohol thermometer 

 verified by comparison, and the weighings were made on a 

 Becker balance. In the experiment, 558.9353 grams pure 

 mercury were placed in the flask, which was filled with alco- 

 hol whose coefficient of expansion was known, the whole 

 placed in the freezing mixture, the mercury frozen, the alco- 

 hol brought exactly to the mark, the temperature noted, the 

 flask set aside to acquire the temperature of the balance- 

 case, cleaned, and weighed. As a final result, the number 

 14.1932 was obtained as representing the density of solid 

 mercury at its fusing-point, 38.85 C, referred to water at 

 its point of maximum density, 4 C. taken as unity. 



Jevons has continued his researches on Pedesis, the name 

 which he has given to the well-known Brownian movement 

 of microscopic particles. To decide between the hypothesis 

 that this movement is due to surface tension, as some hold, 

 and the one which ascribes it to chemical or electromotive 

 action, held by the author, Jevons made the experiment in a 

 solution of soap. Since soap lessens the surface tension of 

 water without affecting its conductive power, the pedesis, if 

 due to surface tension, should be lessened by it. The reverse, 

 however, prov.ed to be the fact, the pedetic motion becoming 

 considerably more marked on the addition of soap, even when 

 not only china clay, but also ferric oxide, chalk, and barium 

 carbonate were employed. The author believes from his ex- 

 periments that the detergent action of soap is due to pedesis, 

 by which minute particles are loosened and diffused through 

 the water, so as to be readily carried off. The high cleansing 

 power of rain or distilled water, in contrast with that of im- 

 pure hard water, is due to the fact that the electric conduc- 

 tivity of the former is lower, and hence pedesis is higher. 

 The addition of salts to water increases its conductivity, but 

 diminishes its pedetic and detergent power. If the salts be 



