CHEMICAL AND PHYSICAL NOTES. 87 
has been lowered: therefore we see that the cryohydric temperature 
of a mixture of NaCl and KCl must be lower than that of NaCl 
alone ; and it is quite independent of whether the cryohydric tem- 
perature of KCl is high or low. 
Imagine now that KCl and NaCl, not only crystallise in the same 
system, but are isomorphous in the restricted sense, which is char- 
acterised by the formation of “mixed crystals.” It is then obvious 
that in the saturated solution, the particle of NaCl when prevented 
from uniting with another particle of NaCl to form a crystal, will 
simply unite with the particle of KCl which stands in the way, and 
will crystallise. Consequently, if the solution of NaCl were originally 
not quite saturated, the introduction of the KCl, by increasing the 
amount of crystallisable material, would make it saturated. Hence, 
if KCl and NaCl were isomorphous and formed mixed crystals, the 
cryohydric temperature of a mixture of the two salts would be 
higher than that of the NaCl. 
The nitrates of barium, strontium and lead are isomorphous salts 
which form mixed crystals. In boiling mixtures, it has been shown * 
that nitrate of strontium raises the condensing temperature of steam 
by 6°°53 C., and nitrate of lead raises it by 3°°29 C., while the 
mixture = (NO )2 raises it by 5°°98C.; and the quantity of 
condensed steam required to produce the boiling saturated solution 
of the mixture is exactly the sum of the amounts required for the 
ingredients separately. In the case of the nitrates of strontium and 
barium, the elevation of the condensing point is not as great as with 
Sr(NO,), alone: the maximum temperature does not remain constant 
for a minute, and the condensed steam required to dissolve the mix- 
ture is about 25 per cent. more than is required to dissolve the salts 
separately. 
Similarly in the case of freezing mixtures, the following cryohydric 
temperatures were observed: nitrate of barium —0°°7 C., nitrate 
of strontium —5°°75 C., and nitrate of lead —2°°7 C.; and the 
cryohydric temperatures of pairs of these salts in equal molecular 
proportions: nitrates of strontium and barium —5°*73 C., nitrates 
of strontium and lead —5°°23 C., and nitrates of lead and barium 
—2°°53 0, 
The case of the isomorphism of salts which form mixed crystals 
is a feature of salts and solutions which has no analogy in the 
physics of gases. 
* ‘On Steam and Brines,” by J. Y. Buchanan, F.R.8. Trans. R.S.F. (1899), vol. 
xxxix. p. 547. 
