The following examples show the effect of hydration on heat of solution in a large quantity of water: § io.
On Put-in-Bay Island are some interesting "hydration" caves, i.e.
It is not necessary that there should be present sufficient water to dissolve the whole of the reacting substance at any one time; it is sufficient if there is enough for hydration and a small surplus for the crystallization by successive stages as above described.
It has a remarkable retarding effect on the hydration of the calcium aluminate, and consequently on the setting of the cement; thus it is that a little gypsum is often added to convert a naturally quick-setting cement into one which sets slowly.
It will be observed that in the hydration of tricalcium silicate, the main constituent of Portland cement, a large portion of the lime appears as calcium hydroxide, i.e.
Under this term are comprehended all cements whose setting properties primarily depend on the hydration of calcium sulphate.
It is assumed that each molecule of solute combines with a molecules of solvent according to the ordinary law of chemical combination, and that the number a, representing the degree of hydration, remains constant within wide limits of temperature and concentration.
It appears that the relatively enormous deviations of CaC1 2 from Raoult's law are accounted for on the hypothesis that a=9, but there is a slight uncertainty about the degree of ionization of the strongest solutions at-50° C. Cane-sugar appears to require 5 molecules of water of hydration both at o° C. and at loo° C., whereas KC1 and NaCI take more water at loo° C. than at o° C. The cases considered by Callendar (loc. cit.) are necessarily limited, because the requisite data for strong solutions are comparatively scarce.
But the agreement is very good so far as the data extend, and the theory is really simpler than Raoult's law, because many different degrees of hydration are known, and the assumption a = i (all monohydrates), which is tacitly involved in Raoult's law, is in reality inconsistent with other chemical relations of the substances concerned.
How those clothes will monitor my health, my hydration levels, and even my body odor.