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‘I Srer., 1897. | QUEENSLAND AGRICULTURAL JOURNAL. * 253 
Chemistry. 
By J. C, BRUNNICH, 
Agricultural Chemist. 
PRACTICAL DETERMINATION OF THE STARCH-CONTENT OF 
POTATOES. 
Wuen potatoes are judged, generally only the most striking points, such as 
time of growth, crop, shape and appearance of the tubers, skin, flesh, &c., are 
taken into consideration, and the most important point, the starch-content of 
the potatoes, on which their value as a food mostly depends, is completely 
overlooked. : 
The composition of the potatoes depends on a good many factors—not only 
on the variety, but also on weather during growth, cultivation, soil, &e. The 
ayerage composition of a good class of potatoes is— 
Per cent. 
Water ... cs nk fee ae Rene DAC) 
Nitrogenous substances aay es PHY) 
Woody fibre ... 0 wae 200 3x: m3) 
Ash, salts, &c.... an see a) so | AD) 
Starch ... cx sex: chs use 202 
100°0 
‘ 
These figures show that the chief part of the dry substances is starch, and 
this starch-content may vary from 10 per cent. to 26 per cent. Climate, soil, 
manuring, mode of cultivation, variety will all influence this content of starch ; 
and every farmer should try to find a variety of potatoes which suits his soils 
and other circumstances best. 
The operation itself to determine the starch value is so easy, quick, and 
costless that every grower should know how to use it. As arule the following 
varieties contain about 18 to 20 per cent. of starch :—Snowflake, Extra Early, 
Vermont, Early Rose, Brownell’s Beauty; 20 to 22 per cent. is found in 
Bressel’s Prolific and Late Rose ; 22 to 24 per cent. in Peerless. 
The determination of the starch-content is based on the fact that the dry 
substances of which, as already said, starch forms the chief part are heavier 
than water; and consequently potatoes, which are rich in these dry substances, 
will have a higher specific gravity than poorer, more watery potatoes. 
Weight of body. 
Th ifi ity of a body... ~ 
RE a le u Weight of equal volume of water. 
