152 RESEARCHES UPON THE CHEMICAL PROPERTIES OF GASES. 



potassium acidulated by sulphuric acid ; (2) through a glass tube containing cotton 

 coated with precipitated oxide of copper; (3) through alkaline permanganate; 

 (4) the gas was kept in contact with bromine water for twenty-four hours ; (5) well 

 washed by soda solution (for the action of copper oxide as a purifying agent for 

 hydrogen, see Lionet, Fresenius Zeitsclirift, 1880, p. 344). I have found precipitated 

 carbonate of copper in moist condition to answer better than the oxide, especially for 

 removing sulphuretted hydrogen. Hydrogen so purified contained only traces of a 

 paraffin which, calculated as CHj, amounted to less than 0.02 per cent, of the hy- 

 drogen. By very careful tests no phosphorus, arsenic, sulphur or antimony could 

 be found. 



Expt. 1. — A mixture was made of hydrogen and air in the following proportions : 



Air 80 



Hydrogen 20 



This mixture, contained in a gas-holder, was caused to flow slowly over 6 per cent, 

 palladium asbestos, which was contained in an one-eighth-inch glass tube heated in 

 the oven. The rate of flow of the hydrogen and air mixture could be controlled by 

 causing it to bubble through sulphuric acid before entering the palladium asbestos 

 tube. Some anhydrous copper sulphate was placed in the far end of the palladium 

 tube, which by its change of color to a bright blue serves as a delicate moisture 

 indicator. 



TEMPERATURE OF ASBESTOS TUI5E. RATE OF GAS FLOW. RESULT. 



20^ 100 cub. cenl. in five niin No moisture. 



80O. " " - " ■' " " 



40O •• .< " '• " " " 



50° " " " " " " Moisture formed. 



20'^ " " " " " " No moisture. 



30° " " " " " " " 



40O " " " " " " " 



50° " " " " " " «' . 



5.jO " " " " " " iloisture formed. 



Hence, absolutely dry hydrogen is not easily burnt by palladium asbestos below a 

 temperature of 50°-60°, 



At the above rate (100 c.c. in five minutes), there is a strong tendency to cause 

 glowing of the palladium asbestos, not throughout, but in minute points where the 

 palladium had accumulated in thicker particles. This glowing may take place while 

 the tube is at any temperature between 15° and 100°, and depends wholly on the rate 

 of flow of the hydrogen mixture. It is independent of the temperature outside the 

 tube, and it is therefore not possible to prevent or arrest it except by reducing the 



