Gelatin crystallisation

To 2 ml. of the ester, add 2--3 drops of a saturated freshly prepared solution of scdium bisulphite. On shaking, a gelatinous precipitate of the bisulphite addition product (D) of the keto form separates, and on standing for 5-10 minutes usually crystallises out. This is a normal reaction of a ketone (see p. 344) hydrogen cyanide adds on similarly to give a cyanhydrin. 

Nordmark, T. S., Ziegler, G. R. (2002a). Spherulitic crystallisation of gelatinized maize starch and its fractions. Carbohydrate Polymers, 49,439 48. 

Titanyl Tetrarsenite, (TiO)5As4Ou, is obtained by the action of potassium tetrarsenite in excess on an almost neutral solution of titanyl sulphate. The gelatinous precipitate first formed gradually crystallises. The arsenite dissolves in adds without decomposition, but is insoluble in aqueous potassium hydroxide or ammonia. It decomposes when heated. 

For lower acidity, < 0.5 M HCI, the available literature data are evaluated to allow the conelusion that the degree of polymerisation increases with time and temperature, until finally hydrous zirconia, a gelatinous amorphous phase, precipitates with anion contents varying with pH. It is shown that for this process the tetramers do not need to be dissociated. In hydrous zirconia sols, Zr atoms are connected by hydroxyl bonds, which can be replaced by halogen ions. Refluxing leads to the oxolation of these bonds, to acidification by release of anions and to crystallisation of cubic and monoclinic crystallites and to the formation of colloidal sols. Initial crystallites contain about 12 to 24 unit cells (48 to 96 monomer units). The crystallites still contain large quantities of water and hydroxyl ions, which are supposed to be located at the surface of the Zr02 crystallites. 

Acidic and basic amino acids, like glutaric acid, aspartic acid and lysine, are also isolated from protein hydrolysates for artificial nutrition. The fractions are filtered off under sterile conditions and further purified by crystallisation. Since the BSE crisis, the supply with amino acids has come under scrutiny manufacturers had to assure regulators and customers likewise, that their starting material does not originate from cattle. Mostly used are poultry feathers and pork gelatine. [62]... 

The first to propose a gel structure of the kind discussed here were Gerngross and Herrmann. A diagrammatic picture of the structure of a gelatin gel given by these authors is reproduced in Fig. 7. Similar ideas have been put forward by various other authors with regard to cellulose gels and other objects Further support to the theory of crystallisation is afforded by the observation that gelation is facilitated by inoculation of the solution with particles of the geP. 

We shall forbear from treating this subject in detail and confine ourselves to the statement that volume changes, either a contraction (gelatin-h water) or a dilatation (methyl cellulose -h water), have been frequently observed to accompany the sol-gel transformation. Since this is a common feature of any process of crystallisation or dissolution, no particular importance is to be attached to these phenomena. In the gelatination of thixotropic 9% sols of iron hydroxide, where gel formation is not due to a process of crystallisation, no volume change was observed. 

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