42 PRACTICAL AGRICULTURAL CHEMISTRY [l 10-111 



oven ; after this time brush the dry linseed-powder from its 

 surface. Grease-marks will be found on the paper, showing 

 that the cake contained oil. This oil not only helps in 

 forming the fat of the animal feeding on it, but it also helps 

 in the development of animal heat. 



1 10. Albuminoids in Oil-cakes. — Albuminoids are 

 essentially the flesh-forming compounds in the cake, and 

 they are distinguished from other constituents by the fact 

 that they contain nitrogen. Mix a little powdered linseed- 

 cake with soda-lime and heat some of the mixture in an 

 ignition-tube. Ammonia will be given off, and may be tested 

 for with moist yellow turmeric-paper as described in para- 

 graph 85. This ammonia is formed by the action of soda- 

 lime on the nitrogen of the albuminoids. 



* in. Carbohydrates in Oil-cakes. — The name 

 'carbohydrate' is given to a large class of bodies containing 

 the three elements, carbon, hydrogen, and oxygen. Starch, 

 sugar, and dextrin are examples of carbohydrates. Most of 

 these bodies, on being heated for some time with dilute sul- 

 phuric acid, are converted into grape-sugar. Half fill an 

 evaporating-basin with dilute sulphuric acid (the ordinary 

 dilute acid used in the laboratory must be mixed with twice 

 its volume of water for this experiment). Throw on to the 

 surface of the acid liquid at much powdered linseed-cake as 

 can be held on a penny. Boil gently over a Bunsen flame, 

 supporting the basin on a tripod and pipeclay triangle. Add 

 a little hot water from time to time as the liquid evaporates, 

 to prevent the acid becoming too strong. When it has boiled 

 for five minutes remove from the flame, allow to cool, and 

 filter. Grape-sugar must now be tested for in the clear 

 solution. This is done by adding potash to the acid solution 

 until it is slightly alkaline, then a few drops of Fehling's 

 Solution (266), and heating. The blue colour of the 

 Fehling's Solution will be destroyed, and a light-red or yellow 

 precipitate of cuprous oxide will be formed. 



