64 S. L. Harding—Bichromate of Soda Cell. 
either the expense or care of the battery is an element to be con- 
sidered, the superiority of the soda cell would be especially felt. 
In the case of the single liquid bichromate cells also, the 
superiority of the sodium salt seems to be maintained, though 
it is more difficult to form a correct judgment from the records 
of these cells, owing in part to the greater irregularity of suc- 
cessive records, and in part also to “the fact that the greatest 
and most marked fall in the strength of the current occurs dur- 
ing the first hours of the records, while in the double liquid 
cells the reverse is the case, the most rapid fall occurs during 
the last hours and thereby indicates more accurately the close 
of tue record. Figures 2 and 3 give several of the single liquid 
records, the conditions of which are contained in the following 
table: 
Single Liquid Cells. 
Hours before 
Depolarizer. External resist. exhaustion. 
Series 6 ----- Bichr. of potash 8 ohms 29 
Serles//)(2 eas Bichr. of soda 8: ohms 35 
Series 8 .....Bichr. of potash 35 ohms 67 
Series 9 _._-- Bichr. of soda 45 ohms 714 
Though the difference in the number of hours before ex- 
haustion in the two cells, as indicated by the above table, is 
not so great asin the double liquid cells, a glance at the records 
shows that the weakening of the current in the case of the 
potash cells was more sudden, and that it took place earlier 
than in the soda cells, so that the average strength for the 
whole time was greater in the latter cells. 
An interesting question arises as to the cause of the greater 
power of the bichromate of soda. Both the bichromate batter- 
ies belong to the general class which provides oxygen to unite 
with the hydrogen set free at the negative electrode. The 
question, therefore, resolves itself into this: which salt can 
provide the greater amount of oxygen to unite with the hydro- 
gen? Now our chemical reactions for the two salts are exactly 
similar, chromic acid being given off in both cases, as can be 
seen by writing out the intermediate reactions of (A) and (B). 
Thus: 
(A) (1) Na,Cr,O,+H,SO,=Na,SO,+2Cr0,+H,O 
(2) 2CrO, +6H=Cr,0, +3H,0 
(3) Cr,O,+3H,SO,=Cr,(SO,),+3H,0 
(4) Cr,(SO,), + Na,SO,=Na,Cr,SO,), 
and a similar set for (B). } 
That salt, therefore, which can for a given weight of the 
solution furnish the most chromic acid will prove to be the 
superior. The solubilities of the two salts are as follows: at 
