THE ELECTROCHEnlICAL E Q U I V A U , E S T O F CARBON BE'
H.C. PEASE
Coehnl has determined the electrochemical equivalent of carbon ivlien anode in concentrated sulfuric acid, and has found that carbon is tetravalent under these circumstances, the weight of a gram equivalent being three grams. There are no satisfactory data as to the weight of a gram equivalent of carbon when this substance is anode in fused potassium hJdroxid, and the investigation of this point was, therefore, undertaken at the suggestion of Professor 13ancroft. It is not possible to make the determinations merely by weighing tlie carbon anode before and after the run, because the electrode takes a p a very considerable quantity of the electrolyte. ,It first it was hoped that the amount thus absorbed might be estimated with some approach to accuracy by deterinining the gain in weight of a carbon cathode during the rim ; but this proved impracticable, owing to the rapid disintegration of tlie cathode. T h e experiments were, therefore, maee with a carbon anode and an iron electrode ; in other words, with the Jacques cell. At the end of the run, the carbon was washed in boiling water until the latter gave no test for alkali. I t was then submitted to a temperature of about 2 2 5 ' C. until all the inoisture was driven off. There were tn.0 soiirces of error here. Firstly, the canstic potash might not be entirely washed out, and yet the mater give no test for alkali. Secotidly, the water might not be entirely driven off. On account of tlie hardness of the carbon, it was not found practicable to reduce it to powder before washing. T h e two operations of washing and of subsequent drj.ing I
Zeit. Elektrochetriie, 3 , 424 (189'7).
39
Electrochenzicnl Equianleul of Cni-bon
were therefore carried on mucli longer than n as apparently nececsary. T w o checks were also used to make certain that the caustic potash had been removed entirely. Tlie carbons were washed and dried several times until their weight was constant to within five milligrams. ,Ifter the final weighing the carbon was ground np,the polvder washed and the wash-water evaporated to dryness. If the caustic potash had been conipletely removed, no solid residue would remain. In 110 case was any trace of potassinm hydrosid or potassium carbonate found. One of the carbons was washed in cold instead of hot water, and it was found that even in this wa! all the caiistic potash could be removed. Five experiments were made, the clnantitj- of electricity being kept as near coiistaiit as might he. while the current and time Laried. T h i s was done to detect any change clue to the variation in the strengtlt of the current. Tlie time varied from one and a half to five lioiirs, and the current froin one aiiipere to ( n e r three. T h e results are given in Table I.
TABLEI ~
~
~~
_
_
Time iii hours
1.5
2.0
Ampere hours Average current Carbon in grams Equivalent n eight
4
3.1j 0.~560
4.72 z.
