J. M. Ordway on Nitrates. 15 
60°F, Its density was now 1:90. The contraction may be 
rendered appreciable by the eye, if we cool to a certain degree 
some aniten nitrate contained in a long necked flask, fill with 
an oil up to a marked height, effect the crystallization, and then- 
cool to the same point as before. 
To illustrate the absorption of heat during the liquefaction of 
solids, freezing mixtures are commonly employed in which one 
of the ingredients, ice, is already cold. The experiment is more 
striking when all the articles used are at the temperature of the 
surrounding air. Such may be the case if we take crystallized 
sulphate of soda and a sesquinitrate. A mixture of 36 grams 
of powdered pernitrate of iron crystals and 57 grams of fine 
Glauber’s salt, liquefied and lowered thermometer from 65° F. 
to zero. It readily froze water contained in a test tube. In cold 
weather, 8 grams of the nitrate and 9°5 grams of the sulphate 
brought the thermometer from 22° to —10°. * 
tion is of the right strength to crystallize. But the quantities 
© 
cooled to 83° without becoming solid, we see that to make this 
midsummer the evaporation of the weak solution must 
ll the boiling point gets nearly or quite up to 
peratures of incipient ebullition, crystals were taken that were 
not entirely dry to start with, and the correctness of the indi- 
cations was judged of after ascertaining the solidifying points of 
the residues. 
There is, of course, no definite limit to the cooling which a 
melted salt may undergo without beginning to crystallize. I 
* Nitrate of iron is pretty corrosive, and should not be touched with the fingers. 
