628 BUNSEN MEMORIAL LECTURE. 



were conducted bv Bunsen in colUibonition with Des Cloizeaux. He 

 first shows that the cylindrical shaft, which is no less than 74 feet deep 

 and 10 feet in diameter, had been built up by the deposition of the 

 silica which the water holds in solution, so that, in Tyndairs words, 

 "the o•e3^ser is the architect of its own tube." Bunsen determined the 

 temperjiture of the water contained in the tube a few minutes before 

 an eruption, and found that in no part of the tube did the water reach 

 its boiling point. The situation at which the temperature of the water 

 most nearly approached the boilinj^ point under the superincumbent 

 pressure was about 8(» feet from the bottom, reaching there 121.8'-', 

 whereas the boiling temperature was 123. 8*^, making a difference of 

 only 2 . The question occurs. Why, under these circumstances, does 

 an eruption take place? This is satisfactorily accounted for by the 

 fact that, owing to the (existence at the base of the geyser tube of 

 volcanic vents, through which steam under pressure is passing, the 

 whole column of heated water is lifted, so that while originally at a 

 point ;->() feet from the bottom the temperatui'e of the water was below 

 the boiling point, when it bccanu' raiscnl through a height of ♦» feet b}^ 

 the pressure of the issuing steam its temperature was 1° above the 

 boiling ])oint. the same being true for every point in the cylinder, and 

 thus the cl>ullition gradually increased until at last it became eruptive. 

 An experimental illustration of Bunsen's geyser theory is described b}- 

 Tvndall in his well-known work. 



The distinct shade of l)lue possessed by waters of the geyser Ic^d 

 Bunsen to examine the color of distilled water (Edin. New Phil. 

 Journ., 184l» (47), '.••')). For this purpose he inclosed carefully puri- 

 lied distilled water in a horizontal tube 2 meters long, closed ))y plate- 

 glass ends, the interior of which had been blackened, thus showing 

 that the absorptiA'e power of water is exerted less upon the blue than 

 upon the other rays of the spectrum, and explaining the blue color of 

 certain lakes and rivers and the color of sea water as observed in the 

 Blue Grotto of Capri. Tlu^ differences in depths of shades of blue 

 possessed })v waters in various places are doubtless due to the variation 

 in size of the suspended particles varying in their reflective power. 



Of a totally difterent character was the next piece of work to which 

 I shall refer; it related to the separation of the metals of the platinum 

 group. 



In 1868 (Annalen, 1868 (146), 265) Bunsen worked for some time 

 on methods of separating the several metals contained in the resi- 

 dues left after the process of extracting the i)latinum as practiced in 

 the imperial mint at St. Petersburg. He fully describes the some- 

 what complicated processes by which he effected these separations: (1) 

 The elimination of platinum and palladium; (2) the separation of 

 ruthenium; (3) the deposition of iridium and rhodium; and (4) the 



