I40 CHEMISTR V FOR A GRICUL TURAL STUDENTS 



prepared commercially by the action of dilute acid on starch. " Milk 

 sugar " is a constituent of milk, and can be obtained by evaporating the 

 whey of milk. On warming with acids it is converted into equal quantities 

 of grape sugar and a sugar called "galactose." " Maltose" is the sugar 

 first produced by the action of acid or diastase on starch ; the acid, however, 

 further converts it into grape sugar. In addition to the foregoing carbo- 

 hydrates, gums belong to the same group. The "arabin" of gum-arabic 

 has the formula C12H22O11. 



The relation of the carbohydrates to each other will be best 

 understood by reference to the table on the opposite page. 

 The formulae show that the action of dilute sulphuric acid 

 in converting starch, cellulose, and dextrin into malt sugar, and 

 maltose, cane sugar, and milk sugar into fruit sugar, grape 

 sugar, and galactose, is a process of hydrolysis^ i.e. the decom- 

 position of a substance by water, thus : — 



XXX. THE HYDROCARBONS 



The conversion of wood into charcoal is essentially decomposi- 

 tion of cellulose into carbon and water. This carbonisation 

 takes place in nature. Peat and lignite are partially carbonised 

 vegetable matter, bituminous coal more completely, while 

 anthracite consists almost entirely of carbon. The following 

 results of analyses show the progressive carbonisation that has 

 taken place : — 



