84 Barus — Nuclei produced by Shaking Different Liquids. 



I hope, however, by keeping the drum in rotation around the 

 axis of vision as already suggested to counteract this discrep- 

 ancy and correspondingly to prolong the series. 



4. Carbon disulphide. — The vapor of this reagent is another 

 in which coarse normal coronas usually appear. The endeavor 

 to produce the higher coronas with sulphur, punk or air nuclei 

 fails if the pressure differences are of the same order as those 

 used for water. Particles of the fog are usually about d = 

 •001 cm in diameter for strong nucleation, and the dense coronas 

 produced on shaking showed diameters of the order of d = 

 •0015 under the given conditions of exhaustion. Relatively 

 large coronas were obtained with nuclei which apparently rise 

 from this reagent spontaneously. Thus after about 2 hours 

 d = -002, after 6 to 15 hours d = '0012 cm was observed. The 

 fact that the coronas increase in size in the lapse of time sug- 

 gests other explanation than the slow diffusion of vapor or the 

 difficulty in keeping it uniformly saturated when successive 

 exhaustions are made. For in this case coronas would decrease 

 and the size of the particles increase, whereas the reverse is 

 observed. 



The computation of the number of nuclei per cubic centi- 

 meter for carbon disulphide is more precarious in view of the 

 high vapor pressures and the deficiency of data applying 

 throughout the range of temperature involved. For the case 

 of a pressure decrement of 8p — 18 cm from 76 cm , and at 20°, 

 the adiabatic fall of temperature would be as far as — 34°, the 

 rise therafter due to condensed liquid as far as 5°. This 

 implies 53X10" 6 grams of fog particles per cubic centimeter, 

 whence with the above goniometer the number of nuclei per 

 cubic centimeter would be n = 34 (10 s) 3 — '10/(10 d)\ 



The coronas obtained by spontaneous nucleation thus corre- 

 spond to n = 13,000 after three hours and n = 50,000 after 6 

 hours or more. Finally punk nuclei after two or three exhaus- 

 tions with shaking were still present to the number of n = 

 75,000 per cubic centimeter. 



Brown University, Providence, E. I. 



