April 2^, 1881] 



NA TURE 



599 



of all Bunsen's work. He seeks for the explanation of 

 the fact that hitherto the reduction of these metals 

 by the electric current had proved a failure, and he 

 finds it in what he terms the density of the current, 

 i.e. the electromotive force divided by the area of the 

 pole, the power of the current to overcome chemical 

 affinity increasing with its density. Thus if a constant 

 current be led through an aqueous solution of chromic 

 chloride, the result as to whether hydrogen is evolved, and 

 oxide of chromium, or whether metallic chromium is 

 deposited, depends upon the area of the pole through 

 which the current passes into the liquid. 



Nor were these experiments made merely for the 

 purpose of preparing the metals in question. Thus the 

 metallic magnesium was pressed into wire and used in 

 one of the series of photo-chemical researches, to which 

 reference will hereatier be made, for the purpose of 

 drawing an interesting conclusion respecting its light- 

 giving power on combustion, and comparing this with 

 the visual and chemical brightness of the sun, a compari- 

 son which led to the commercial manufacture of this 

 metal by the Magnesium Metal Company, and to the 

 wide distribution and general use of this metal as an 

 illuminating agent of great brilliancy. Thus again the 

 electrolytic preparation in the Heidelberg laboratory of 

 coherent masses of cerium, lanthanum, and didymium, 

 had the further object of the determination of the specific 

 heat of these metals by help of the now well-known 

 method with Bunsen's ice-calorimeter, by means of which 

 determination the true atomic weights of these metals 

 and the proper formulas of their oxides and compounds 

 have been definitely ascertained. 



The Bunsen battery has however not only been of 

 service in inorganic chemistry, but has thrown clear 

 light upon the constitution of organic bodies. The clas- 

 sical researches of Kolbe on the electrolysis of acetic 

 acid and the other fatty acids were carried out in the 

 Marburg laboratory, and ow-e their inspiration to Bunsen. 

 The subsequent equally important labours of Kolbe 

 and Frankland, and those of the latter chemist alone, 

 on the isolation of the organic radicals, have a like 

 origin. 



Amongst the numerous physico-chemical investigations 

 which Bunsen has carried out, none perhaps show more 

 clearly the fertility of his experimental ability than the 

 one in which he describes the ice calorimeter, and another 

 devoted to an explanation of a new method of determining 

 vapour densities. Translations of these memoirs are 

 found in xh.^ Philosophical Magazine ior \%6y and 1871, 

 and may be taken as typical of his calorimetric re- 

 searches. 



Another group of researches is formed by those which 

 are closely related to his gasometric methods. One of the 

 most interesting and important of these refers to the law 

 of absorption of gases in water. This subject was first 

 examined by Dalton and Henry at the beginning of the 

 century, and the well-known law which gases follow in 

 absorption is known by the names of these two Manchester 

 philosophers. But although generally admitted, its limits 

 of error had not been ascertained, and the crude experi- 

 mental methods of the year 1S03 required to be replaced 

 by the refined ones of the latter half of the century. 

 These researches, carried on by Bunsen and by several of 



his pupils, proved that Henry's law of direct — as well as 

 that of Dalton of partial — pressures is exactly true within 

 certain limits ; but ceases to be so beyond a given increase 

 of pressure, whilst some gases which obey the law at one 

 temperature do not do so at others, and some again whilst 

 obeying it in the pure state, do not do so when mixed with 

 other gases. 



The mere tnention of his other researches in the wide 

 field of gaseous chemistry is sufficient to indicate his 

 devotion to this branch of experimental inquiry. We find 

 experiments on laws of gaseous diffusion, on applications 

 of gaseous diffusion in gasometric Analysis, on the phe- 

 nomena of the combustion of gases, on the temperature 

 of ignition of gases, and all these, be it remembered, 

 involving exact measurement, and in many cases elaborate 

 calculations. 



Brief reference must next be made to a series of investi- 

 gations in a totally different direction, viz. on the measure- 

 ment of the chemical action of light, with the carrying 

 out of which the writer of this article had the great good 

 fortune and pleasure to be connected, and in which he 

 had full opportunity of admiring Bunsen's untiring energy 

 and wonderful manipulative power. In all the difficulties 

 and perplexities by which the experimental investigation 

 of such a subject is beset, the w-riter never knew Bunsen 

 discouraged or at a loss for an expedient by which an 

 obstacle could be overcome. Cheerful and self-reliant 

 under the most depressing circumstances, he never gave 

 up hope, and thus it was that these somewhat intricate 

 and difficult investigations were brought to a successful 

 close. 



Again, in the department of Analytical Chemistry how 

 numerous and valuable have been his contributions ! There 

 is scarcely one important problem in this subject which 

 has not benefited from his extensive experience and keen 

 insight. Bunsen's methods of silicate analysis, of mineral 

 water analysis, and a dozen of other complicated laboratory 

 processes, are simply perfect. Then his original method 

 for the estimation of nitrogen in organic bodies will 

 always be remembered as one of the most accurate of its 

 kind when employed by an experimentalist as expert as 

 Bunsen himself, but as most difficult and even dangerous 

 in less able hands. Again, all chemists use and appreciate 

 the much simpler methods for the estimation of nitrogen 

 and sulphur admirably worked out by his pupils — Maxwell 

 Simpson and Russell. 



We all employ his beautiful general method of 

 volumetric analysis, but chemists do not always re- 

 member that in this research Bunsen first determined 

 the exact percentage composition of the higher oxide 

 of cerium, a determination of the greatest scientific 

 itnportance as regards the chemistry of the metals 

 of the rare earths. Moreover they may be apt to 

 forget that Bunsen was the first to introduce a general 

 method of the separation of these rare earths, by which 

 he for the first time prepared pure yttria and erbia, and 

 by which subsequently, in the hands of other chemists, 

 many new metals have been discovered. His well-known 

 method of flame-reactions is a standard example worked 

 out by every student. Again, modern chemists can now 

 scarcely carry on the simplest experiment without using 

 the " Bunsen gas-lamp," a burner which is also now 

 employed in every household, and in many manufactories, 



