182 M. K. Bunsen on the Law of Absorption of Gases. 



The experiment gave therefore, in fact, rather a smaller coeffi- 

 cient. In spite, however, of the most careful purification, the 

 mercury always caused a black turbidity in the water, which 

 perceptibly increased with agitation. This circumstance, and 

 the fact that the coefficients determined one after the other in 

 the same liquid and at the same temperature always regularly 

 increased, showed that this method was not to be relied upon 

 for exact results. I have preferred, therefore, to determine the 

 coefficients by an indirect method. 



If atmospheric air perfectly free from carbonic acid and am- 

 monia be passed into boiled water, the amount of oxygen absorbed 

 V , and the amount of absorbed nitrogen V, is found from the 

 following equations formerly deduced : — 



y- " p OV. ■ . (3) 



0- 0-76(N + O)' K ' 



_^PNV 1 _ ... (4) 



The first of these equations divided by the second gives 



NV • • 



— -°/3 = «. As the composition of atmospheric air, i. e. the pro- 



ov 



N 



portion j=r, as well as the absorption-coefficient /3 of nitrogen is 

 U y 



known, we only require to determine the proportion ^, or the 



composition of the air dissolved in the water, in order to calcu- 

 late a* or the absorption-coefficients of oxygen. The elements 

 for this calculation are found in the following experiments. The 

 air, perfectly freed from carbonic acid and ammonia, was passed 

 in a strong stream for half a day through the water, previously 

 well boiled, which was kept at a constant temperature by immer- 

 sion in a water-bath. The purification of the water must be 

 conducted with the greatest care. It must not be distilled in 

 any vessel previously used for any organic preparation, as the 

 slightest trace of volatile organic matter present is sufficient to 

 convert a part of the oxygen into carbonic acid. It is therefore 

 necessary to prove the absence of carbonic acid in the air boiled 

 out from the water by a special experiment. The gases dissolved 

 in this water were collected by a method which I made use of in 

 my researches upon the gases of the islandic springs, and more 

 fully described by Dr. Baumert, in his admirable research upon 

 the respiration of the Cobitis fossilis. 



