Thus far, nothing further than simple mixture, as when coloured water was added to pure water, seems to have occurred; but, in reality, something more has happened. In the first place, the mixture is a good deal warmer than either of its components; that is to say, =heat= has been =generated=. In the second place, if you measure the volume of the whole fluid after it has cooled, it no longer stands at the mark =ten=, but distinctly lower, or about =nine and three-quarters=. As the volume of the mixture is less than the sum of the volumes of its two components, it follows that the =density= of the mixture must be =greater= than a density midway between that of the water and that of the alcohol. In other words, the molecules in the mixture do not occupy the same space as they did when they were separate. The result is the same as if the ten volumes had been compressed until they occupied only nine and three-quarters; so that the effect is a contraction similar to that which would be brought about by taking away heat from the mixture. In fact, as we have seen, the mixture gives out a quantity of heat. There is another respect in which the mixture is unlike both its constituents. It both =boils= and =freezes= at a much =lower= temperature than =water= does, and at a =higher= temperature than =alcohol= does. In fact pure alcohol has not yet been frozen. If the molecules of the alcohol were merely diffused among those of the water as water is diffused through wet sand, they ought to pass into the gaseous state at the same temperature as that at which alcohol boils; and it would then be very easy to separate alcohol from water by distillation. But the fact is not so; alcohol cannot be obtained free from water by distillation unless something which holds water very strongly, such as quicklime, is added, so as to keep all the water back when the fluid is heated. Thus alcohol and water, mingled together, give rise to a fluid which is not a mere mixture, the properties of which are known if we know the properties of its components; it is, in strictness, a new body, in which the molecules of the water and those of the alcohol affect one another to a certain extent and modify the pre-existing properties of each. This effect of different bodies upon one another becomes much more manifest when water is brought into contact with certain solids. 53. =Solution; Water Dissolves Salt.=