RESEARCHES UFON THE CHEMICAL PROPERTIES OP GASES. 175 



2. The gas was collected in glass-stoppered bottles over water, a small quantity 

 of a solution introduced by means of a tap funnel with the lower end of its stem 

 bent upward, then the bottle closed and kept inverted at any given temperature for 

 sufficient length of time (usually from a few months to several days) to ascertain if 

 a reaction had occurred. The former method answers well for gases which are easily 

 controlled in a slow continuous stream and obtainable in large quantity. The latter 

 method is more economical as regards the gas to be used, and is better suited to 

 gases where some slight but difficultly removable impurity is suspected to occur of 

 a character liable to effect the reagent (such as the traces of hydrocarbons present in 

 hydrogen made from zinc and sulphuric acid). In such cases the smaller the volume 

 of gas to be used in a trial the better. A reaction may usually be obtained with 

 from 20 to 50 c.c. of gas. Small bottles having well-ground, flat-topped glass stop- 

 pers answer well, as they may be kept standing inverted and may, if heat is to be 

 applied, be placed inverted in boiling water. It is hardly necessary to add that, 

 when inverted, such bottles may be used to hold gas in contact with a reagent for 

 long periods without danger of loss. 



HYDROGEN". 



Hydrogen for the following experiments was prepared and purified as already 

 described (p. 151). Keactions were tried in bottles and by causing the gas to bubble 

 through the solutions, as just detailed. 



1. Reactions in Solution. 



REAGENT. REACTIONS. 



Palladium chloride The solution is slowly hut completely reduced, cold or at 



100°. The precipitated palladium usually collects as 

 a black powder. Sometimes it is deposited as a film 

 on the glass. 



Platinum chloride* Very slow but complete reduction, cold or at 100^. The 



reduced metal appears as a blacli powder. 



Gold chloride Unchanged. 



Silver nitrate Unchanged if the fluid contains a trace of free nitric acid. 



Ammoniacal silver nitrate Slowly reduced, the silver appearing as a blacli powder 



Iridium chloride Unchanged. 



Rhodium chloride • Unchanged. 



Potassium rutheniate Slowly reduced. The orange color of the fluid disappears 



and metallic ruthenium is precipitated as a black 

 powder. 



Cerium dioxide dissolved in dilute sulphuric acid Unchanged. 



Potassium permanganate,! neutral Extremely slow reduction, the purple color changing to 



brown. 



* Mendeleeff, Pl-inciples of Cliemistry, Vol. II, p. 353. 



f Meyer and Askenasy {Ber., 1882, p. 410, R) find that electrolytic hydrogen reduces potassium permanganate. 



