66 REPORTS ON THE STATE OF SCIENOE.—1917. 
tenacious or glutinous sols than the others, and for particular purposes 
certain starches may be found more suitable than others. 
Starch absorbs a certain amount of water from the atmosphere ; this 
varies with the conditions, but is usually from 13 to 15 per cent. ; it also 
contains a small proportion of mineral matter, which is, in all cases, 
alkaline ; this amounts in potato-starch to about 0-22 per cent., sago 0-4, 
cassava 0-12, maize 0-11, and wheat 0-23, therefore in dealing with natural 
starch we have to take into account the influence the electrolytes in this 
mineral matter will have upon the starch molecules. 
On heating with water no action whatever is apparent until a tempera- 
ture of about 55° C. is reached, when it is noticed that a few granules have 
swollen enormously ; from this point onwards there is a progressive increase 
in the number of swollen granules, till at a certain temperature all the 
granules have become fully hydrated and most, if not all, have burst, 
although the granules can still be observed more or less distorted. The 
temperature at which this occurs is the maximum thickening-point of the 
mixture, this occurring with wheat-starch at 65° C., maize 70°, sago 72°, 
rice 74°, and potato-starch 63°. 
The viscosity of solutions made from different starches varies ; thus, 
G. M. MacNider (‘ Journ. Ind. and Eng. Chem.’ 1912, 4, 417-422) found the 
viscosity of potato-starch to be 14-31, maize 2-49-2-86, cassava 3-88-3-97, 
wheat 1-24-1-26, and rice 1-00 for solutions containing 12 grams in 30 «.c. 
of water. These figures need verification, as the differences appear to be 
very much greater than one would suppose possible, although, no doubt, 
a certain amount of variation does really exist. It was noted also by 
the above observer that very small quantities of borax (7.e., 08 gram) and 
of caustic soda (06 gram) lowered the viscosity, while larger quantities 
(7.e., 1-0 gram) increased it, the viscosity being also lowered by boric acid. 
Since writing the above, the author has found that the time factor is 
most important. For instance, freshly prepared and quickly cooled 
potato-starch solution of 2 per cent. concentration gave the following 
figures (water = 1) :— 
Fresh. 5 min. later. 40 min. later. 18 hours later. 
106°7 96:3 19:3 
At the last period quite a considerable quantity of the starch granules 
had deposited, leaving a clear liquid on the surface, which could be filtered. 
The viscosity of starch solution does not therefore increase, as with 
other colloids, with the time. 
It was at one time believed that starch granules consisted of two distinct 
substances, an inner material or granulose (amylose), and an outer material 
named starch cellulose or amylopectin ; but according to Harrison (‘ Journ. 
Soc. Dyers and Colourists,’ 1916, 32, 40-44) the outer portion of the starch 
granules does not differ in composition from the inner material although it 
is more resistant to hydrolytic agents. By physical means alone they are 
capable of being changed one into the other. Z. Gatin-Gruzewska and L. 
Macquenne (" Compt. Rend.’ 1908, 146, 540-545) also conclude that there is 
a structural relationship between amylose and amylopectin, and that 
probably each is composed of a series of closely related substances. 
The addition of certain substances to starch and water lowers the surface 
tension of the granules so that the thickening-point is more or less 
depressed ; this is especially the case with caustic soda, zine chloride, and 
