The Romance of Modern Chemistry

SUGAR AND STARCH this method is generally derived from potatoes or maize; it is made into a cream with water, and then run into boiling dilute sulphuric acid. In these circumstances the starch undergoes a gradual change, which the chemist describes as “hydrolysis,” and the boiling is continued until starch can no longer be detected in the liquid. The test is made by taking a sample out of the boiler, cooling it, and adding a little iodine, which gives a blue colour so long as unchanged starch is present. Possibly the reader may at some time or other have accidentally dropped a little tincture of iodine on a starched article, say a shirt-cuff, and noticed that a deep blue stain was produced. This is a very characteristic peculiarity of starch, and always serves for its detection. The solution of glucose obtained after hydrolysis is complete must, of course, be freed from the acid, which would be a most undesirable constituent of any food-stuff, 'fhe cooled liquid is accordingly neutralised with chalk or whiting, and the insoluble sulphate of lime which is formed is filtered off. It ia further necessary to de- colorise the solution by means of animal charcoal, and to concentrate by evaporation until the solid can be obtained. The glucose produced in this way will be a white sub- stance, provided sufficient care has been taken to de- colorise the solution thoroughly by animal charcoal; otherwise the substance will have a light brown tinge. If the conversion of the starch should have been in- completely carried out, then a liquid glucose syrup is finally obtained, which, although not so pure as the solid glucose, may be used, and is extensively used, both in confectionery and brewing. Other carbohydrates as well as starch can easily be 232