Chenucal Constitution of Saline Solutions. 297 
hydrochloric acid, In that of calcium chloride we have a similar action, but 
it is not so energetic. The action of alcohol has been clearly ascertained (see 
p. 272) to be also that of a dehydrating agent exerted upon the crystalline 
hydrate in solution. The dehydrating action of glycerine is aided by a rise 
of temperature. 
Let us now consider the action of a solvent which is not a dehydrating agent. 
When six parts of uranyl nitrate UO(NO;),6H,0, or more precisely 6:1 parts, 
are dissolved in 4:4 parts of washed ether, the crystals enter into a perfectly 
definite and clear state of solution, from which they may be recovered unaltered by 
spontaneous evaporation. The ether is saturated with water, and it cannot there- 
fore dehydrate the salt; but when 7, ¢.c. of water is mixed with 10 c.c. of this 
ether, or in the proportion of 1 volume of water to 100 of ether, the water 
separates as a distinct layer. But the solution of uranyl nitrate contains 1°307 
parts of water in combination, or 21°43 per cent., and yet there is no separation 
into two layers of liquid. If the specific gravity of the ether be taken as 0°75, the 
proportion of water by volume to ether is as 1°307 to 3:3. Hence the water 
molecules in this solution form an integral part of the molecule of the uranium 
salt, and do not exhibit the physical properties peculiar to water. If, however, the 
uranyl nitrate crystals are moist, the moisture separates from the ether as an 
aqueous solution of the salt. 
I. Conctuston.— When a definite crystalline hydrate dissolves in a solvent which is 
not water, and is not a dehydrating agent, the molecule of the salt remains intact. 
The Effect of Heat on Absorption Spectra. 
When saturated solutions of coloured salts are heated to 100° C., there are few 
cases in which no change is noticed; generally the amount of light transmitted 
is diminished to a small extent by some of the more or less refrangible rays 
being absorbed. There is frequently a complete difference in the nature of the 
transmitted light. Anhydrous salts not decomposed, hydrated compounds not 
dehydrated at 100°, and salts which do not change colour on dehydration, give 
little or no alteration in their spectra when heated. 
Solutions of hydrated salts, and most notably of haloid compounds, do change ; 
and the alteration in the spectra, if not always absolutely identical with, is at least 
very nearly the same, as that produced by dehydration and by the action of dehy- 
drating liquids (such as alcohol, acids, and glycerine) on the salts in the crystalline 
state or in solution. Allowance must be made for changes in the absorption spectra, 
owing to differences in the solubility of the anhydrous and the hydrated compounds 
at the particular temperature, and also in some cases for the different action of 
solvents on the spectra. The reason of this may be indicated by stating that the 
