170 COMPOSITION OF THE BODY 



fatty acid is liberated and rises to the top in drops. Shake with a 

 few cc. of ether. Draw off the ether and allow a drop of it to 

 evaporate on a glass slide. Examine for crystals of fatty acids. 



Stearic acid crystallizes in long rhombical scales or plates. 

 Palmitic acid appears in tufts of fine needles. Oleic acid crystal- 

 lizes at about 4° C. 



7. Test for oleic acid. Evaporate the ethereal solution of the 

 fatty acids. If part of the remainder does not solidify at ordinary 

 temperature it is probably oleic acid. Separate it from the solid 

 acids and add concentrated sulphuric acid and a little cane-sugar. 

 With this treatment oleic acid gives a beautiful red or reddish 

 violet color. 



238. The Determination of Organic and Inorganic Matter. 

 Weigh a crucible carefully and place in it the finely divided tissue 

 for determination. Weigh again and then place the crucible in a 

 thermostat to dry at no C. When successive weighings show 

 no decrease in the weight of the substance it may be considered 

 dry and a simple calculation will give the weight of the water and 

 its percentage. The dry material in the crucible may now be ig- 

 nited. For this purpose the crucible should be placed on a wire 

 triangle and the flame of a Bunsen burner applied beneath. Care 

 should be taken that the temperature is not too high. A dull 

 red color at the bottom of the crucible is usually indicative of 

 sufficient heat. All carbon should be carefully burned from the 

 crucible by tilting it on its sides. Carbon which persists in the 

 ash should be worked to the bottom of the crucible with a needle 

 or other small instrument when it will usually oxidize. When 

 burning is complete, cool the crucible and weigh carefully. This 

 weight minus the weight of the crucible gives the amount of 

 inorganic substance in the material. 



239. Inorganic Constituents. The quantity and variety of the 

 mineral substances found in any plant depends on the composition 

 of the soil in which it grows. Certain substances however, are es- 

 sential for the growing plant and among these are calcium, potas- 

 sium, magnesium and iron. These are not present in the metallic 



