COMPOSITION OF ORGANIC COMPOUNDS 31 



6. Other Elements. 



Amongst natural compounds the most important other elements 

 combined with carbon are iron, e.g. iron in haemoglobin, ferrocyanides, 

 and magnesium, e.g. magnesium in chlorophyll. Copper is found in 

 certain other animal pigments. Silicon is present in certain vegetables, 

 e.g. in grasses. Organic silicon, arsenic, antimony and magnesium 

 compounds have been prepared in the laboratory. These elements 

 are best detected after the organic matter has been completely re- 

 moved by burning either alone or in the presence of an oxidising 

 agent (fusion mixture). Thus : 



Detection of Iron in Haemoglobin. A small portion of haemo- 

 globin is heated in a crucible with 3-4 times its quantity of fusion 

 mixture until all the organic matter has been oxidised. The mass, 

 when cold, is dissolved in dilute hydrochloric acid. The solution is 

 filtered and the filtrate is tested for ferric salts with (a) ammonium 

 thiocyanate and (b) potassium ferrocyanide. 



B. QUANTITATIVE COMPOSITION. 



ESTIMATION OF THE ELEMENTS. 



i. Carbon and Hydrogen. 



An organic compound on oxidation with copper oxide is con- 

 verted into carbon dioxide and water. The amount of each element 

 contained in the compound is determined by weighing the carbon 

 dioxide and water produced from a known weight of the compound. 



FIG. 15. Combustion Furnace, 



The analysis is carried out in a long tube of hard glass, a com- 

 istion tube, about 80 cm. long, which is heated in a furnace (Fig. 15). 



