Chemistry and Physics. 151 



call attention to this remarkable mimicry of ionic dissociation. 

 Are these slowly moving molecules conveying two currents in a 

 way at all analogous to conduction by ions? Curiously enough, 

 in some of these separations a banded structure has been ob- 

 served, recalling the phenomenon of stratification in gases. — J. 

 Chem. Soc, lxxi, 568-573, May, 1897. g. f. b. 



2. On the Phenomena of Super saturation and Supercooling.— 

 The phenomena attending the solidification of supersaturated 

 solutions and of supercooled liquids have been studied by 

 Ostwald. By suitably selecting the substances used, he has 

 avoided the influence of dust particles; and he then finds that 

 solidification is brought about only by the introduction either of 

 a crystal of the same substance or of one strictly isomorphous 

 with it. Thus fused salol, melting at 39*5°, cannot be made to 

 crystallize at common temperatures by any of the ordinary means. 

 But if ..a fine glass thread be drawn over a salol crystal, it will 

 induce crystallization; though it loses this power by exposing it 

 to the air for a few minutes, by wiping it with rubber, or by 

 warming it to 40°. The author finds, however, that the tempera- 

 ture range below the melting point in which spontaneous produc- 

 tion of crystals is impossible, is quite limited, the liquid being in 

 stable equilibrium except towards a ready formed crystal. To 

 this condition he gives the name metastable. At lower tempera- 

 tures, no nuclei are necessary, the crystals forming spontaneously. 

 Moreover it appears that there is an inferior limit to the quantity 

 of substance required to start the crystallization, the two methods 

 tried, successive dilution on the one hand or the evaporation of 

 progressively more dilute solutions on a platinum wire on the 

 other, giving identical results. In the case of sodium chlorate, a 

 solution containing 107 parts of the salt in 100 of water can be 

 made to crystallize by the introduction of a millionth or even a ten 

 millionth of a milligram. That a minute fragment of ammonium 

 alum causes a solution of potassium alum to crystallize, he ex- 

 plains by supposing the diffusion of the dissolved salt into the 

 solid particle as soon as it comes in contact with the solution. 

 The author concludes that when a system passes from any given 

 condition to a more stable one, it will not pass into the state 

 which under the circumstances is the most stable, but into that 

 which is nearest to the original state. — Zeitschr. f pliysikal. 

 Chemie, xxii, 289, April, 1897. g. f. b. 



3. On a Thermochemical Method for determining the Equiva- 

 lents of Acids and Bases. — A thermochemical method has been 

 proposed by Berthelot by means of which the equivalent of an 

 acid or a base may be determined even when the compound is of 

 unknown composition. For this purpose a given weight, p, of the 

 acid is made up to a given volume, say two liters, with distilled 

 water. A convenient quantity, say 500 cc , is taken, and 100 cc of 

 potash solution (KOH = 2 liters) added, the heat produced, q x , 

 being measured. Then a second 100 cc are added and the heat, q„ 

 is measured ; the process being continued n times until no more 



