THE COMPOSITION OF PLANTS AND ANIMALS 153 



by heat and cooled in a desiccator. Weigh into this dish lo.o g. of 

 dry grass, straw or leaves. Heat the dish slowly, testing the volatile 

 products as in (i). Heat with full flame until all free carbon has been 

 oxidized. When only a light gray ash is left, cool the dish in a desic- 

 cator and weigh. Subtract the weight of the dish from the weight 

 of dish and ash to obtain the weight of ash. Calculate the per cent 

 in the original material. The difference between this and 100 per 

 cent will give the per cent of volatile or organic constituents in the 

 original substance. In the ash obtained from most mixed plant and 

 animal materials we may show the presence of the following metallic 

 elements and salts: (i) sodium, Na, potassium, K, calcium, Ca, 

 magnesium, Mg, carbonates, NaoCOs, nitrates, KNO3, phosphates, 

 Na3P04, sulphates, K2SO4, chlorides, NaCl. 



(b) Evaporate 25 c.c. of milk, blood, urine or saliva slowly to dry- 

 ness and repeat (a) with dry residue. 



