14° Journal of Agricultural Research voi.vii,no. 3 
cylinder of fine platinum gauze approximately i cm. long. Near the 
upper end of the electrode a branch tube permits the entrance of hydro¬ 
gen gas. A platinum wire is affixed to the gauze at one end and sealed 
into a small glass tube at the other. The electrical connection is then 
made by the use of a copper wire and a mercury cup, as shown in figure 
i. The electrode must be gas-tight at the top. Platinum black is de¬ 
posited on the gauze, as described by Ostwald (22). The coating should 
be renewed occasionally. It is sometimes necessary to clean the plat- 
