232 Revieivs — Dr. J. W. Evans — Geological Collecting. 



gases were consequently already burnt and mixed with air. To obtain 

 unburnt gases the authors made descents into the crater, at considerable 

 danger to themselves, and pumped the gases through a set of tubes 

 the end of which, cased in iron, extended for a foot into a vent in 

 a dome of lava on the crater-floor. In fifteen minutes, during which 

 1,000 litres of gas may have passed through the glass tubes, the 

 authors obtained about 300 c.c. of water. A second attempt was 

 made to collect the gases in vacuum tubes and so find the relative 

 proportions of the constituents, but the experiment was vitiated by 

 access of air from another vent ; however, the figures obtained indicate 

 that water was present to the extent of 26 per cent by weight. It 

 is therefore clear that water does play an important role in the 

 emanations from Kilauea, and that Brun's conclusions in this respect 

 are false. Many of Brun's arguments are based on observations of 

 the cloud over the lava in the crater pit of Kilauea and on hygroraetric 

 measurements, but it is shown that his deductions from these observa- 

 tions were incorrect. 



Further interesting deductions may be made from the study of the 

 emanations of Kilauea. The gases detected include nitrogen, hydrogen, 

 water, carbon dioxide, carbon monoxide, hydrogen, and sulphur, with 

 traces of chlorine, fluorine, and, possibly, ammonia. These gases 

 issue from vents in the lava at a temperature near 1,000° C, 

 a temperature at which they cannot possibly be in equilibrium under 

 atmospheric pressure. Diminution in pressure may cause interactions 

 which probably produce a heating effect far exceeding the cooling- 

 effect due to expansion; thus the gases may be hotter at the surface 

 than in depth. In support of this idea it is noted that the temperature 

 of the lava rises with the quantity of gas given off. With regard to 

 the origin of the water, the authors find themselves unable to conceive 

 of any mechanism whereby atmospheric or surface waters could reach 

 the magma basins. Further, the very important fact that argoti is 

 absent in the emanations of Kilauea proves that atmospheric gases 

 have not reached the magma basins. The water of the emanations 

 "must be considered as an original constituent with as much right 

 as the sulphur or the carbon". 



VII. — Directions poe, the Collection of Geological Specimens. 

 By Dr. J. W. Evans, LL.B., F.G.S. Colonial Office, Miscell. 

 No. 283. 



UNDER this title the Colonial Office have issued a tract by Dr. J. "W. 

 Evans, giving explicit instructions as to what to do and what to 

 avoid. It cannot be too often said that many of those who travel to 

 little-visited parts of the world are entirely ignorant of the simplest 

 geological knowledge, and with every intention of bringing home 

 specimens often collect useless material. In this tract the traveller 

 is told exactly what is likely to be of use, how to obtain it, how to 

 label and pack it, and how to make his notes on what is collected. 

 The few pages (twenty) will hardly form impedimenta in his baggage, 

 and the knowledge he will obtain from a perusal of the tract will, 

 even if he does not happen to do any collecting, greatly increase the 



