THE STRUCTURE OK THE NUOLEtTS. 



79 



the occurrence of peculiar conditions of e(iuili!>riuiM. (Cf. Chapter V, 4ji^ 44, 47, 

 48, or, below, §30.) 



13. Benzine. SpontdneouH luidcatwib. — The main occui'veiices lia\e already 

 been given. With air nuclei (s — SiO, d— .0029 cm., and larger), the coronas may 

 be removed iu two exhaustions. Spontaneous nucleation does not occur. A clean 

 vessel examined an hour later was still clean; examined next day, it i-emained so. 



14. Coronas and axial color. — The following table is an example of the 

 occurrence of strong axial color, all the more noteworthy as the diameter of the 

 vessel was only 23 cm. The occuirence of the initial fog in the upper half of 

 the vessel is I'are, but the nuclei came fi'om a sulphur flame. 



TABLE 4.— BEHAVIOR OF SULPHUR NUCLEI IN BENZINE VAPOR. 

 (}LOBE, 23 cm. IN OIAMErER. EXHAUSTION, 76-59 cm. 



' Abbreviations as in table 2. 



15. Petroleum. Coronas and axial colors. — The behavior of peti'oleum pre- 

 sents a wide divergence from the preceding instances of very volatile hydrocai'bons. 

 A full series of coronas is pi'oducible, in every respect like those for water as to 

 color sequences, though nothing can be stated as to the i-elative size of the nuclei in 

 action. The axial colors show a like succession, though naturally they ai-e weaker, 

 from the small quantity of vapor available. For the same reason the coronas are, 

 as a rule, larger than those of water obtained under like conditions. 



Petroleum is not free from a tendency to produce stratified coronas ; the tables 

 show that annuli, differently colored above and below their centers, soon occur, and 

 that the intei'ferences met with on shaking the liquid cannot be avoided if annular 

 coronas are wanted. 



