THE CHEMISTRY OF COOKERY, 67 



Serious consequences have resulted from ignorance of this, as shown 

 in the practice of feeding invalids on arrowroot. The popular notion 

 that anything which thickens to a jelly when cooked must be propor- 

 tionally nutritious is very fallacious, and many a victim has died of 

 starvation by the reliance of nurses on this theory, and consequently 

 feeding an emaciated invalid on mere starch in the form of arrowroot, 

 etc. The selling of a fancy variety at ten times its proper value has 

 greatly aided this delusion, so many believing that whatever is dear 

 must be good. I remember when oysters were retailed in London at 

 fourpence per dozen. They were not then supposed to be exceptionally 

 nutritious and prescribed to invalids, as they have been lately, since 

 their price has risen to threepence each. 



The change which takes place in the cookery of starch may, I 

 think, be described as simple hydration, or union with water ; not that 

 definite chemical combination that may be expressed in terms of chem- 

 ical equivalents, but a sort of hydration of which we have so many 

 other examples, where something unites with water in any quantity, 

 the union being accompanied with an evolution of some amount of 

 heat. Striking illustrations of this are presented on placing a piece of 

 hydrated soda or potash in water, or mixing sulphuric acid, already 

 combined chemically with an equivalent of water, with more water. 

 Here we have aqueous adhesion and considerable evolution of heat, 

 without the definitive quantitative chemical combination demanded by 

 atomic theories. 



In the experiment above described for separating the starch from 

 wheat-flour, the starch thus liberated sinks to the bottom of the water, 

 and remains there undissolved. The same occurs if arrowroot be 

 thrown into water. This insolubility is not entirely due to the inter- 

 vention of the envelope of the granules, as may be shown by crushing 

 the granules while dry^ and then dropping them into water. Such a 

 mixture of starch and cold water remains unchanged for a long time — 

 Miller says " an indefinite time." 



When heated to a little above 140° Fahrenheit, an absorption of 

 water takes place through the enveloping membrane of the granule, 

 the grains swell up, and the mixture becomes pasty or viscous. If 

 this paste be largely diluted with water, the swollen granules still re- 

 main as separate bodies, and slowly sink, though a considerable exos- 

 mosis of the true starch has occurred, as shown by the thickening of 

 the water. It appears that in their original state the enveloping mem- 

 brane is much folded, the folds probably forming the curious marking 

 of concentric rings, which constitutes the characteristic microscopic 

 structure of starch -granules, and that, when cooked at the temperature 

 named, the very delicate membrane becomes fully distended by the 

 increased bulk of the hydrated and diluted starch. 



A very little mechanical violence, mere stirring, now breaks up 

 these distended granules, and we obtain the starch -paste so well 



