BUNSEN MEMORIAL LECTURE. gJQ 



methods Of eudiometric analysis, giving details c,f manipulation, with 

 a discnsaiou in each case of the pro].a),le sources of error and <,f the 

 means of their limitation. As a model of accurate work (his oxv.n^n 

 determinations in air showed differences of 0. 1 per cent on th«> oxvXn^) 

 Bunsen s eudiometric methods will always r.Muain as the standard 

 More expeditious and simpler methods have been introduced of l-ite 

 years, but none of these equals the original processes in exactitude 



The third portion of the volume consists of a description of two 

 new methods for determining the specitic gravity of gases. The Hrst 

 of these, which also applies to the case of vapJrs, consists in weigh- 

 ing a tared vessel, tilled tirst with the gas or vapor under examina- 

 tion and then with air, all variations due to change of temperature and 

 pressure being eliminated by a simple and ingenious compensating 

 arrangement. Perhaps the most interesting portion of this section is 

 a description of a new thermostat, by means of which perfectly con- 

 stant temperatures up to a high point can be obtained. This served 

 Bunsen for ascertaining the specific gravity of aqueous vapor at 

 diflVrent temperatures, and closely accordant numbers were ol^taincd, 

 although the weight of vapor amounted to only 80 milligrams. The 

 second method, applicable only to gases, depends on the determination 

 of the rates of diffusion of the gases into air. Here, too, the \ ohiine 

 of gas operated upon need not exceed 50 to (>0 cubic centimeters, and 

 yet the results obtained are extremely accurate. On this |)()int 

 Bunsen remarks that for technical purposes — as, for example, for 

 the determination of the density of coal gas — the above simple method 

 will probably be found preferable to all other ])rocesses. 



The fourth part contains a series of investigations on the absorptio- 

 metric phenomena of gases in water and alcohol, the experiments 

 having been chiefly undertaken with a view of determining th(^ limits 

 to which the well-known laws of pressure hold good. Fir>( Im' 

 describes his absorptiometer, a new instrument by means of which it 

 is possible to obtain accurate numbers with relatively small volumes 

 of the gases. The absorption coefficients of no fewer than twenty- 

 seven different gases in water and alcohol were determined by methods 

 varying according to the nature of the case, partly carried out by 

 himself and partly by many of his pupils, the result being that certain 

 gases, generally those least soluble in water, are found to l)e in accord 

 with Dalton's law of pressures and Dalton and Henry's law of partial 

 pressures, whereas the more soluble gases are not always in ac<-ord 

 with them. In the former class it is i)()ssible, from an experimental 

 determination of the coefficient of absorption, to calculate the conqx*- 

 sition of the original gas, the composition derived from an absorptio- 

 metric analysis being found to agree exactly with that obtained by 

 direct eudiometric measurements. It is also p(»ssible to ascertain 

 whether a given gas consists of a single substance t»r is a mixliire of 



