SOLUBLE stahch. 103 



cxLi, 1247) discovered that malt infusions react toward tincture of giiaiacum like solu- 

 tions of compoimds of iron or manganese. If the malt infusion yields only a faint guaiacum 

 reaction, the addition of traces of alkaU, or aeration and acidifying with lactic acid, causes 

 it to give a full reaction. The preparation after this treatment has lost its power of sac- 

 charifymg, but not its power of liquefying starch-paste. Solutions having the power of 

 liquefying starch-paste at 20° were made by treating a solution of commercial albumin 

 with ferrous and ferric oxides. It was also found that the starch-liquefying action could 

 be considerably intensified by the addition of lactic acid or asparagin. 



The liquefaction of starch-paste under pressure may be hindered by the presence of 

 certain substances. Thus, Fernbach and Wolff (Compt. rend., 1906, cxliii, 380) found 

 that while salts which are neutral to methyl orange are without effect, salts that are alkahne 

 are inhibitory, and that traces of alkali may be absolutely preventive. Green (The 

 Soluble Ferments, London, 1901, 31) records that the "diastase of secretion" corrodes 

 starch-grains and disintegrates them before solution, and rapidly hquefies starch-paste, 

 most advantageously at a temperature of 50° to 55°, and that it will withstand heating 

 to 70° without destruction. 



Ford (Jour. Soc. Chem. Industry, 1904, xxiii, 414) prepared soluble starch by previ- 

 ous treatment of the raw starch with dilute alkaU and acid, repeatedly washing, and then 

 drying in the air. This purified starch was gelatinized, then Uquefied at 79° to 80° by 

 means of a trace of diastase, and then the limpid solution boiled to destroy further cUas- 

 tatic action. Ford also prepared a soluble starch that was practically ash-free by repeated 

 precipitation of an acidified solution of starch with alcohol, with the addition of a very 

 small quantity of potassium or sodium chloride to prevent the starch from becoming 

 milky, which results from the entke removal of acid or salts. Soluble starch prepared 

 in this way is described as fairly pure and nearly neutral; that is, it does not give a reac- 

 tion with rosolic acid or methyl orange, although somewhat acid to phenolphthaleine. 



O'Sullivan, Brown and Heron, and many other investigators have prepared soluble 

 starch by arresting diastatic action at the proper time. 



A non-colloidal or perfect solution of starch was made by Fouard (Compt. rend., 1908, 

 cxlvi, 285) by demineralizing the starch, and partial hychation at 80°. The preparation 

 thus obtained can be filtered through a collodion membrane, a 5 per cent solution of col- 

 loidal starch jdelding in tliis way a 2.74 per cent non-colloidal solution. Fouard states 

 that tliis non-colloidal solution shows not a trace of polarization ; that it gives an intensely 

 blue reaction with iodine, appearing as a solution rather than as a suspended precipitate; 

 that its \'iscosity is about that of a 1 per cent solution of sugar, and, therefore, nearly that 

 of water; that it is unstable, becoming cloudy and forming a granular deposit; and that 

 it is probably a heterogeneous system containing dissolved molecules together with starch- 

 molecules in all degrees of condensation. In a subsequent study, Fouard (Compt. rend., 

 1908, CXLVI, 978) found by ultra-microscopic examination that this non-colloidal solution 

 stands intermediate between mineral colloids of insoluble elements and a perfectly disso- 

 ciated salt-solution. Freezing causes a slight opalescence preceding the formation of 

 granules. When a 5 per cent pseudo-solution is filtered through several collodion mem- 

 branes which differ in their density, by varying the proportions of alcohol the filtrate 

 contains increasing proportions of colloidal starch, ranging from 1.518 to 2.365 per cent, 

 and having an increasing rotatory power (a)u = from 183° 15' to 191° 50', showing that 

 the membrane acts as an analyzer. The state of perfect solution is changed by dilu- 

 tion or evaporation in vacuo. The water therefore not only acts as a solvent, but also 

 is a necessary factor in modifying the state of the starch. During the granular formation 

 the solution shows a very slight acidity, such as might be caused by completely dissociated 

 acid phosphate; and the electric conductivity slowly increases, corresponding to the for- 

 mation of the granules and the Uberation of nuneral ions. 



