208 



RESEARCHES UPON THE CHEMICAL PROPERTIES OP GASES. 



tube B is pushed down so that some of the soda solution is forced over into the 

 manganous chloride solution, causing a precipitation of manganous hydroxide. This 

 precipitate remains white in the absence of oxygen. If oxygen be present, it grad- 

 ually darkens in changing to Mn.Os. On adding now a little iodide of potassium 

 solution and then sulphuric acid, by the tap funnel, the oxide of manganese redis- 

 solves, liberating iodine, recognizable by its color even when the most minute traces 

 only of oxygen are present. The same apparatus can be used for pyrogallol and 

 soda. 



U 



NaOH 



Solution 



=^ 



=0 



(T 



MnCl^ 



SolutlOTZ 



The method above described is very satisfactory in testing for oxygen in pres- 

 ence of paraffins, olefines, acetylene, allylene, carbon monoxide, carbon disulphide 

 vapor. Sulphuretted hydrogen and carbon oxysulphide must be absorbed by ammo- 

 niacal cadmium chloride solution, or other suitable reagent, before the test can be 

 applied. If an ammoniacal cadmium chloride solution is thus used, vapors of 

 ammonia must be absorbed by dilute sulphuric acid before the reaction is tried. No 

 difficulty occurs in applying the same reaction in testing a limited volume of gas. 

 Instead of conducting the gas in a stream through the solutions, a eudiometer may 

 be used. The reaction is, however, far less satisfactory, as the solutions are liable to 

 hold atmospheric oxygen dissolved. By means of a standard hyposulphite solution 

 the free iodine may be estimated ; and, as 254 parts of iodine correspond to 16 parts 

 of oxygen, the latter element is easily detei-mined. 



Pfordten {Fres. Zeit, 1887, p. 74) proposes the use of chromous chloride in 



