340 Mr. Graham on the Heat disengaged in Combinations. 
pure water. The fall of temperature for a whole equivalent 
of bichromate of potash will therefore be 3°96. 
Fall on solution of KO,2 CrO, . . 396 
The heat of liquefaction of bichromate of potash is there- 
fore very considerable. It appears to be the same in quantity 
as that of nitrate of potash. ‘The equivalent quantity of the 
latter salt, 63°25 grains, was dissolved in 1000 grains of water, 
with a fall of 3°86. The temperature of this solution was 
further reduced 0°10, by dilution with another 1000 grains 
of water; so that by the solution of an equivalent quantity of 
this salt in the same proportion of water as was employed for 
the solution of an equivalent of bichromate of potash, a fall 
of temperature of 3°°96 is produced. In a second experiment 
the whole fall of temperature on the solution of an equiva- 
lent of nitrate of potash was 3°95. 
Fall on solution of KO, NO;. . . . . 3°96 
It is possible that this coincidence is not accidental, but 
depends on a thermal equivalency of N O, and Cr, O,, the 
acids united with potash in these two salts. If the single 
equivalent of nitrogen in nitric acid be divided by three, or 
considered three atoms instead of one, as has been inferred on 
other grounds, then the acid constituents of both salts will 
contain the same number of atoms, namely eight; and the 
bichromate of potash, which has hitherto appeared so anoma~ 
lous among salts, be assimilated to the nitrate of potash. 
4. Terchromate of Potash.—Of this salt 63°63 grains, or 
one-half of the equivalent quantity, were dissolved easily and 
entirely by 1000 grains of water, with a fall of 1°63. But 
the terchromate of potash changes colour when thrown into 
water from decomposition, being resolved in a great measure 
into bichromate of potash and chromic acid, both of which 
are soon dissolved, the last more rapidly than the first. 
Half an equivalent of this salt was dissolved, with a fall of 
1°-28, in 1000 water-grain measures of dilute nitric acid, of 
specific gravity 1:1453. But in this menstruum also, the 
terchromate appeared to be decomposed with separation of 
chromic acid, although to a much less extent than in the pre- 
ceding experiment. In a liquid, however, already charged 
with the salt, like the last, an additional quantity may be dis- 
solved without further decomposition. Half an equivalent of 
the salt was dissolved in that liquid with a fall of 1°14, which 
is a fall of 2°-28 for a whole equivalent of the salt. The ca- 
pacity for heat of the solution in question does not (I believe) 
differ materially from that of 1000 grains of water. 
Fall from solution of KO,3 CrO, . . . 2°28 
