ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 67 
hydrochloric acid, which in concentrated solutions form a tenacious white 
translucent gel with starch even at the ordinary temperature ; other 
metallic chlorides behave similarly to zinc chloride, although less marked in 
their action, but the chlorides of the alkalies appeared to be without effect. 
Gels made on these lines, containing 9 to 34 per cent. of starch, 4 to 20 per 
cent. of zinc chloride, and 0 to 19 per cent. of magnesium chloride, are 
sometimes sold for sizing purposes (H. B. Stocks and H.G. White, ‘J.8.C.1.,’ 
1903, 22, and ‘ Jour. Soc. Dyers and Colourists,’ March 1894). 
E. Fouard (“ Comp. Rend.’ 1907, 144, 501-503 and 1366-1368) found 
the amount of phosphoric acid in a starch containing 0-331 per cent. of ash 
to be 0-1915 per cent. By treatment with acid these were reduced to 
0-123 and 0-1117 per cent. respectively, and he is of opinion that the acid is 
absorbed by the insoluble starch granule. Acids have a coagulating effect 
upon starch in proportion to their hydrogen-ion concentration, very weak 
acids having no appreciable effect. Alkalies, on the other hand, have an 
exactly opposite effect, either dissolving the starch or decreasing its 
tendency to coagulation, the retardation being strictly in proportion to their 
hydroxyl-ion concentration. Salts which hydrolyse in solution act upon 
starch in one or other of these directions according to the predominance of 
the hydrogen or hydroxyl-ions respectively. This coagulating effect of the 
hydrogen-ions and the swelling effect of the hydroxyl-ions is general 
throughout the whole of the organic and some of the inorganic colloids, and 
is a capillary phenomenon of the greatest importance. 
The mineral matter of starch can be to a certain extent removed by 
precipitating a dilute sol with alcohol, or, better, by addition of ammonium 
carbonate. Sols of starch purified by these means are very unstable, the 
starch reverting to the insoluble form in very minute granules on standing. 
W. Harrison (‘ Jour. Soc. Dyers and Colourists,’ 1916, 32, 40-44), also 
L. Macquenne (‘ Compt. Rend.’ 1908, 146, 317-318), G. Malfitano and A. 
Moschkoff (‘Compt. Rend.’ 1910, 150, 710-711), by successive freezing and 
thawing of solutions of starch, have obtained it almost free from mineral 
matter which remained in solution in the water. The starch thus prepared 
formed a heterogeneous mixture with water even after heating, and on 
standing the starch settled out again. These authors believe that starch is 
entirely insoluble in water but that in association with electrolytes it 
forms colloidal solutions. 
The Arabol Man. Co. (Fr. Pat. 394,167, 1908) use KCNS for preparing 
starch soluble in cold water, while, according to W. Lenz (‘7th Int. Cong. 
Appl. Chem. Lond.’ 1909), sodium salicylate causes some starch granules, 
though not all, to swell. 
Starch adsorbs alkalies and alkaline earths; the adsorption com- 
pounds, although unstable in water, appear to be more stable in contact 
with alcohol ; thus starch precipitated from a solution in caustic potash by 
alcohol contains potassium in proportion to the strength of the caustic 
potash solution (Hi. Fouard, ‘ Bull. Soc. Chim.’ 1909, 5, 828-834). Precipi- 
tation of starch in presence of barium hydroxide by means of alcohol has 
also been proposed by Asboth (‘ Analyst,’ July 1887; also ‘ Jour. Soc. Chem. 
Ind.’ 1888, 77) as a method of estimating this substance by volumetric 
means, the compound containing 19-1 per cent. of BaO, corresponding with 
the formula C,,H,,.0.,BaO. In order to get concordant results it is 
necessary that certain conditions as to strength of reagents, &c. should 
always be complied with, According to W. Harrison (° Jour. Soc. Dyers 
FQ 
