Hydration difference

The alkylamine hydrate inclusion compounds form a large variety of structures. Phase diagram studies at the end of the last century [7651 (see Tkble 21.3), and an extensive series of phase diagram studies carried out between 1970 and 1981 [798], showed that aliphatic amines form a large variety of hydrates. Relatively few of these have been studied by X-ray crystal structure analysis and none by neutron diffraction [433, 799]. These hydrates differ from the gas hydrates and the alkyl ammonium salt hydrates in that there appear to be no definite structural types into which several hydrates can be classified. Hitherto, a different crystal structure has been observed for every alkylamine hydrate studied. In this respect, they resemble low hydrated crystals. 

Product Distributions. When the reactant ion is hydrated, different reaction channels are possible because different numbers of waters may hydrate the product ion. For example, the reactant 0H -H20 in reaction 4 can form either Cl- or Cl- H20. One channel is available for the unhydrated... 

The hydrocarbons of the benzene series, unlike those previously considered, form two distinct kinds of hydrates, differing from each other materially in their properties. The terms of one of these series exhibit all the functions of the alcohols, and are known as aromatic alcohols. The terms of the other series differ in function from any substance thus far considered, and are known as phenols. The difference between them and the aromatic alcohols is due to the fact that in the phenols the OH is directly attached to a C atom, while in the alcohols it forms part of the group of atoms CH3OH, characteristic of the alcohols ... 

The hydration difference [15, 18, 21) is the difference between of gaseous and /ctem of the corresponding aqua ion. It turns out to... 

The rate of hydration differs in the various calcium sulfates whereas calcium sulfate hemihydrate and anhydrite-111 hydrate rapidly, the hydration of anhydrite-II progresses... 

It has been suggested that these behavioral differences between d- and P-stannic acid can be explained by the. as sumption that the two substances are different collodial varieties of insoluble tin dioxide or its hydrates, differing from one another only by their particle size. Another point of view is that a-stannic acid, mltially present as SnQ2 xH20, condenses under the influence of higher temperature or prolonged time to more thermodynamically stable... 

B Champagnon, G Panczer, B Chazallon, L Arnaud, P Duval, V Lipenkov. Nitrogen and oxygen guest molecules in clathrate hydrates different sites revealed by Raman spectroscopy. J Raman Spectrosc 28(9) 711-716, 1997. 

The Nova DPM 9003 measures hydration even more superficially than the Comeometer—at the level of the stratum comeum only—and is used mainly for measurements of improved skin hydration. Different probe sizes are available depending on the specific testing needs. The instrument is easy to carry (small size) and easy to use (self-calibration, pressure control by means of a spring into the probe, automatic switch when applied to the skin, etc.) it can be used with a battery. A characteristic of the dermal phase meter (DPM) is the ability to record skin surface hydration in a continuous mode, which makes this instrument very suitable for specific studies investigating the kinetics of water desorption from skin [115]. 

The other sulfate hydrates, viz. the nona- and pentahydrate series, behave in a similar way, with a slight difference in the dehydration mechanism. Ce2(S04)3 8H2O and other cerium sulfate hydrates differ by decomposing from the anhydrous sulfate directly to oxide CeOj without step (3). Likewise, 802(804)3 5H2O decomposes without the oxosulfate intermediate (Komissarova et d., 1965b). 

In determining the heat of solution of salts, attention must be paid to whether they are anhydrous or hydrated and in the latter case, to the degree of hydration. Different values for the heat of solution will be obtained according to the state of the solid as regards these factors. 

If the hydration reactions were not changing during the development of hydration, different characterisation methods should provide similar information on the degree of hydration. However, the hydrates do not react simultaneously and the reaction products vary. Nevertheless, reasonable correlation between data obtained with different characterisation methods is observed. 

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