BUNSEN MEMORIAL LECIURE. 631 



to the extraordinary luminous intensity of incandescent orhia, interest- 

 ing- as bein^ the starting point for the enormous industry of the incan- 

 descent mantle. He also determines the meltino- points and the rate 

 of volatility of many salts by means of small beads of material ])laced 

 at the end of a thin platinum wire in the flame, the rate of volatiliza- 

 tion being- ascertained by the microscopic measurement of the dimin- 

 ishing- diameters, in given periods of time, of tlie molten glot)ules. 

 He next details a variety of original and most ingenious methods of 

 detecting minute quantities of the metals and nonmetals by the help of 

 reactions eflected in the flame. So delicate are some of these methods, 

 as, for instance, that of the detection of gold, that its presence can be 

 with certaint}^ ascertained in one centigram of a sample of a tclLuiium 

 ore containing only a few tenths of a milligram of the metal. 



Another most characteristic contribution to analytical chemistry is 

 the investigation of a method of general applicability, published in 

 1853 (Annalen (80), 265). known as the iodometric method and consist- 

 ing of the volumetric determination of free iodine by means of suljihur- 

 ous acid, for which has since been substituted the more stal)le sodium 

 thiosulphate. This method, as every chemist knows, is not only largely 

 emploj'^ed in commercial analyses, as, for example, for the estimation 

 of the amount of manganese dioxide in manganese ores and Weldon 

 mud. but it also gives valuable assistance in the determination of inter- 

 esting theoretical questions, as, for instance, by Bunsen in the sejjara- 

 tion of cerium and lanthanum, and in the estimation of the atomic 

 weight of the former metal. 



Bunsen also devoted much time and labor to the perfection and 

 systematization of the processes of mineral-water analysis. 

 ^ In 1871 he published a detailed account (Zeit. anal. Chem. (1(>), 3ia) 

 of the methods of analysis which he adopted and their i-esults in an 

 investigation, made on behalf of the authorities, which had occupied 

 him for some years, on the chemical and physical properties of the 

 mineral waters occurring in various parts of the Grand Duchy of 

 Baden. These results he afterwards pul)lished in panijililct f..ini. 

 They certainlv constitute the most complete series of ininei-:ii-\v:it.T 

 analvses existing, and serve as a model in this domain of analytical 

 chemistry. It is interesting to rememl)er that Victor Meyer, who 



acted at the time as his assistant, carried out a large ])art of tl xpen- 



mental work. 



Having thus pointed out some of the main f.'atures of Hunsen's sci- 

 entific achievements, 1 now turn to n.y p.Msonal nM-..llectu.ns to give 

 you an idea of what maimer of man he was, and h<.w he I.ve.l and 



worked. , , i w- . i 



Mv reminiscences of Bunsen date as far back as the ya'" l^--- '" 

 the autumn of that year I was introduced to him by 1 lofcssor von 



