41 PRACTICAL AGRICULTURAL CHEMISTRY [116-119 



* 116. Testing Linseed-cake for Starch.— Pour a 



little of the gummy substance prepared in the last experi- 

 ment into a test-tube and boil it. As soon as it has boiled 

 cool it down by allowing the cold water from a tap to run 

 over the outside of the tube. When quite cool add a few 

 drops of a solution of iodine in potassium iodide and shake 

 up. If the cake assume a greenish colour it is pure and 

 free from starch ; if it turn deep blue or black it shows the 

 presence of starch, and therefore it has been adulterated. 



117. Cotton-wool in Cotton-cake.— In the pre- 

 paration of cotton-cake it is necessary to free the seed from 

 cotton-wool. If this be badly done the value of the cake 

 will be much impaired. 



Break up a piece of undecorticated cotton-cake, weighing 

 about two ounces, as finely as possible in a mortar, then place 

 it in a wire sieve having from twenty to thirty meshes to the 

 linear inch. Shake the sieve until all the finer portion has 

 passed through, and examine the husk which is left. Should 

 the cake be an inferior one a small quantity of* cotton-wool 

 will usually be found adhering to it. The wool may often 

 be seen without this preliminary sifting. 



Grass and Hay 



118. Grass and Hay. — All the substances which have 

 been shown to occur in oil-cakes may be found in grass. 

 Some of these, however, such as oil, occur in such small 

 quantities that it would require far more delicate experiments 

 than those detailed in these pages to show their presence. 

 The following experiments, however, are instructive and 

 should be performed. 



119. Albuminoids in Grass.— Cut up a little grass 

 (or hay) as finely as possible with a pair of scissors and 

 grind it up in a mortar with a little sharp sand. This will 

 render it sufficiently fine to mix readily with soda-lime. 

 Mix it with an equal quantity of soda-lime and heat a little 



