194 EESEAKCHES UPON THE CHEMICAL PROPERTIES OF GASES. 



Cerium dioxide iu dilute sulphuric acid Slowly bleached. 



Potassium permanganate Turns brown at once. 



Potassium permanganate in dilute sulphuric acid Quickly bleached. 



Potassium permanganate crystals in concentrated sul- The gas is immediately oxidized to carbon dioxide. 



phuric acid. 

 Potassium bichromate acidulated with sulphuric acid . . The color is unchanged, cold or at 100°. 



Osmic acid Quickly reduced, turning black from precipitated metal. 



Copper sulphate in neutral or ammoniacal solution.... Unchanged. 



Ferric chloride Decided reduction to ferrous chloride, in twenty-four 



hours cold. 

 Calcium hypobromite containing excess of lime water. Acetylene is slowly oxidized, yielding CO,, the lime 



water becoming milky. 



Hydrogen peroxide and lime water The fluid remains clear. 



Bismuth pentoxide in excess of caustic potash solution Unchanged. 



Potassium ferricyanide Unchanged. 



Iodine dissolved in potassium iodide solution Unchanged. The color is not bleached. 



Yellow oxide of mercury Unchanged in color. 



Mercurous nitrate White precipitate. 



Cuprous chloride in ammonia Deep red precipitate, the well-known "copper acety- 



lide." 

 Chromous chloride (CrClj) Is said to absorb acetylene (Roscoe and Schorlemmer, 



Vol. II, Pt. II, p. 160). 

 Mercuric chloride White precipitate. Very delicate reaction. This reagent 



converts acetylene into acetone {Ber., XVII, p. 28, 



and XXI, p. 3344). 



2, Reactions at High Temperatures. 



Iodic acid in crystals was found to be reduced by acetylene at about 90°. In 

 this reaction iodine vapors and carbon dioxide appeared. Aside from the experi- 

 ments on oxidation by finely divided raetals already detailed, no other reactions at 

 high temperatures were tried. 



Comments. — Ammoniacal cuprous chloride, the absorbent commonly recom- 

 mended for acetylene, although a very delicate reagent for the recognition of the 

 gas, is at the same time slow and its action is liable to be incomplete. A single 

 bubble of the gas will cause a decided red precipitate, but acetylene may be passed 

 slowly through a series of Woulfe bottles containing the ammoniacal cuprous 

 chloride solution and yet be very incompletely absorbed, so that it may still cause 

 precipitation in the same reagent. The bright red precipitate dissolves easily in 

 hydrochloric acid, with evolution of acetylene on boiling. This affords a convenient 

 and well-known method for the purification of the gas. Exposed to the air, how- 

 ever, the red compound changes to a deep brownish black and becomes insoluble in 

 acids. Consequently, in preparing and washing the red copper acetylide, with a 



