ON SCIENCE IN SCHOOL CERTIFICATE EXAMINATIONS. 511 



The presence of starch, in considerable quantity, in important food materials, 

 having been thus established and something learnt of its properties, the part it plays 

 in cereal grains may be considered. 



What happens to the seed when it germinates and a plant grows out of it ? 

 Some information will have been gained already on this point. The gradual dis- 

 appearance of the starch will have been noted. By tasting grains which have been 

 soaked in water and then kept for various periods, the development of a sweet taste 

 will be noticed. Malt may then be introduced and an account given of the way in 

 which it is made and what it is used for. Malt should be made by steeping barley 

 in water during .... hours, then keeping it and allowing it to germinate until the 

 young plantlet is about .... inches long, after which it is dried at a temperature 

 not exceeding . . . . C. The appearance of the starch grains of the malted and 

 unmalted barley should be noticed under the microscope. Then equal quantities of 

 barley and of malt which have been ground in a coffee mill should each be mixed 

 with about .... times their weight of ordinary water and the mixture allowed to 

 stand .... hours. It would then be discovered that in one case the starch dis- 

 appears. The liquids should be examined and the weights of equal volumes (the 

 relative densities) contrasted with that of water. Known quantities should be 

 evaporated in weighed dishes on the water bath, in order that the weights of matter 

 in solution might be determined. It would thus be discovered that the starch is 

 changed into a soluble sugar-like material and the disappearance of the starch from 

 the seed during germination would be explained. 



Foster's 'Primer of Physiology' (Macmillan & Co., Ltd., Is.) might be studied 

 at this stage with advantage and the nature of the stomach and intestines made 

 clear. At some time also the stomach and the intestines of a freshly killed rabbit 

 should be laid bare before the class and their character and arrangement fully 

 explained. 



The children might then be asked — What happens to the starch in our food ? 

 What is done with it ? — It is first chewed in the mouth and becomes mixed with 

 spittle or saliva, is it not ? Does this latter produce any effect on it ? Try ! Spit 

 freety into a test tube half full of solidified starch paste prepared as directed ; mix 

 the starch and saliva well together with the aid of a light wooden rod which you 

 have made for the purpose. Plunge the tube into a water bath kept at about . . . C. ; 

 examine it at intervals. Repeat the experiment but first spit into the test tube and 

 then plunge it into boiUng water ; after about five minutes' heating add the starch 

 and digest the mixture : at the same time digest a mixture of starch with similar 

 imheated saUva. Also make comparative experiments in a similar way with unboiled 

 and boiled malt-extract. 



It would then be discovered that starch is rendered soluble by something which 

 is present both in malt-extract and in saliva — something, moreover, which is 

 rendered inactive by heating to near the boiling point of water. This substance has 

 been named Diastase. 



The importance of the change thus undergone by starch when ' digested ' with 

 the aid of the diastase either in malt-extract or in saliva would be more obvious 

 when it is realised that starch diffuses with extreme slowness into water and that it 

 does not pass through wet bladder or vegetable parchment, whereas the sugar which 

 is formed from it on digestion, like ordinary sugar and salt, diffuses readily. 



Our starchy food is cooked either by baking or by boiling it — what is the effect 

 on the starch of baking and boiling 1 



When heated in the oven, as in baking bread or pastry, flour is browned and may 

 easily be burnt ; but flour is more than starch — what happens to starch when it is 

 heated alone ? Study the effect of heat on starch verj' carefully, at gradually 

 increasing temperatures. 



At an early stage, vapour is given off — ^what does this look like ? Steam — that 

 is to say, water vapour. Perhaps the starch was not dry — dry it carefully at a 

 temperature at which wet things are easily dried and repeat the experiment. Vapour 

 is still given off when the dried starch is heated — is it water vapour ? How can you 

 find out ? What happens when water vapour meets a cold surface ? Try ! The 

 vapour becomes liquid — it condenses. See if the vapour from starch can be con- 

 densed. You find it can and that the liquid is like water — is it water ? Would not 

 the discovery that it is water be of interest and importance as an indication that 

 water is in some waj^ contained in starch ? Try therefore to prove that the liquid is 



