S. L. Harding—Bichromate of Soda Cell. 65 
15° C. 100 parts of water dissolve 12°5 parts of the bichromate 
of potash, and 83°16 parts of the anhydrous bichromate of soda. 
The available oxygen, therefore, in a given amount, for instance, 
a litre of the solution, is nearly five times as great for the soda 
salt as for the potash. This explanation, it seems to me, will 
vo far toward accounting for the superior constancy of the 
soda cell. 
In the appended table are contained the above results, and 
others computed with a view of comparing the two bichromates 
with other depolarizing agents of the same general class. The 
first column gives the per cent of oxygen in one molecule 
ot each of the tabulated substances which is available for 
combination with the hydrogen set free; thus, in bichromate 
of potash, three atoms of oxygen, or ‘1629 of the total weight, 
are available. The third column gives the cost of obtaining a 
kilogram of oxygen from each of the oxydizers. In these col- 
umns the fact that the bichromate of soda is hydrous increases 
the total molecular weight, and therevy lowers the per cent of 
available oxygen. In the last column 1s contained the amount 
of available oxygen in a saturated solution of each of the 
soluble depolarizers. As is seen from the table, bichromate of 
soda stands far ahead of the others in the last respect, giving 
8°52 per cent of available oxygen from a saturated solution of 
the salt : 
Per cent of 
Per cent of Number of Cost of Solubility : available 
available oxy- kilogramsto producing 100partsH2O oxygenina 
gen in one roduce one 1 Kilo of dissolve at saturated 
molecule. kiloofoxygen. oxygen. 15° centigrade, solution. 
Bichromate of potash, "1629 6°138 $2:°03 QED .01808 
anhydrous 
83°16 0852 
Bichromate of soda, “160 6°25 1°65 
Peroxide of manganese, ‘092 10°87 1°92 insoluble. 
Permanganate-of potash, °253 3°95 3°34 6°25 "0142 
Nitric acid, C. P., "254 3:93 2°59 
From this table it is seen that the bichromate of soda com- 
pares very favorably with the other depolarizers in all those 
respects which are essential for a good battery. ‘The great 
solubility and large amount of available oxygen indicate great 
possibilities for this salt. - 
This table might be much extended, but, owing to the com- 
plicated nature of the chemical actions which take place in 
many batteries, our knowledge in this direction is very limited 
and consequently we cannot proceed far. 
Electro-motive force. 
The electro-motive force of the soda cell I obtained by the 
open-circuit method of comparison, by means of an electro- 
meter, with a standard (Daniell’s siphon) battery. With- one 
Am. Jour. Sct.—TuHirp SERIES, Vou. XX XIII, No. 193.—JaNnuARy, 1887. 
9) 
