20 THE ECONOMICS OF FEEDING HORSES 



matter, such as chlorophyl. Only the fixed fats and 

 oils are of any value as food, so that the ether extract 

 does not strictly represent the nutritive value from the 

 point of view of fat content, but is slightly in excess of 

 the true value. 



4. The Carbo-hydrates, or ''Nitrog-en- free Extract," 

 may be obtained by treating a known weight of the 

 powdered foodstuff with dilute (1 per cent.) hydrochloric 

 acid and warming the mixture over the water-bath for 

 some hours. This converts some of the starch into 

 sugar, some only into dextrin. The dextrin has to be 

 treated with rather stronger acid, and the mixture boiled 

 for three or four hours, when the whole of the soluble 

 carbohydrates may be considered to have been converted 

 into (glucose) sugar, which can be estimated. 



The more usual method of determining the percentage 

 of carbo-hydrates is by difference — i.e., by subtraction of 

 the total of other components from 100. 



5. Crude Fibre. — To determine the crude fibre, a 

 known weight of the powdered sample is boiled in dilute 

 sulphuric acid for half an hour, the residue filtered off 

 and boiled in dilute caustic potash solution. The residue 

 is then washed, dried, and weighed ( = Wi), then ignited, 

 and the ash weighed ( = W2). Then Wi — W2= crude 

 fibre. 



6. The Ash, or Mineral Matter, is obtained by heating 

 the dried foodstuff to redness in a platinum crucible, 

 continuing the heating until the residue is white, then 

 cooling and weighing. 



Variation in Composition of Foodstuffs. 



In speaking of the chemical composition of a natural 

 foodstuff, it is to be remembered that this is never exactly 



