ELEMENTARY COURSE 



LESSON I 

 THE ELEMENTS CONTAINED IN PHYSIOLOGICAL COMPOUNDS 



1. TAKE a fragment of meat about the size of a pea and place it in a porcelain 

 crucible over a Bunsen flame. Note that it chars, showing the presence of 

 carbon, and that it gives off the unpleasant odour of burning flesh, which is 

 due to the fact that it contains the nitrogenous substances called proteins. In 

 course of time the organic material is completely burnt up, and a small 

 amount of white ash or inorganic material is left behind. 



2. Repeat the experiment with a pure organic substance like sugar. 

 Note that no ash is left. Charring, as before, indicates the presence of carbon, 

 but there is no characteristic smell of burning nitrogenous substances (absence 

 of nitrogen). 



3. The tests for carbon depend on the fact that when this element is 

 oxidised it gives rise to carbon dioxide ; the test for hydrogen depends on 

 the fact that when this element is oxidised it gives rise to water. If all the 

 carbon dioxide and water formed by oxidation from a weighed amount of 

 any organic substance under examination are collected and estimated, the 

 amount of carbon and hydrogen respectively which it contains can be easily 

 calculated. The following exercises, however, deal only with the qualitative 

 detection of these elements. 



4. Tests for Carbon. The following tests can be carried out with sugar. 

 (a) When burnt in the air it chars and subsequently the carbon entirely 



disappears, passing off in combination with oxygen as carbon dioxide (carbonic- 

 acid gas). 



(6) Mix some of the powdered sugar in a dry mortar with about ten times 

 the quantity of cupric oxide (which has been freed from water by previous 

 heating) ; place the mixture in a dry test-tube provided with a rubber cork 

 perforated by a bent glass tube which dips into either lime water or baryta 

 water. Heat the tube over a Bunsen flame, and as the carbon of the sugar 

 becomes oxidised carbon dioxide comes off and causes a white precipitate of 

 calcium or barium carbonate, as the case may be. 



5. Test for Hydrogen. In the experiment just described (4 b) note that 

 drops of water due to oxidation of hydrogen condense in the colder parts of 

 the test-tube. 



6. Tests for Nitrogen. The greater number of tests for this element are 

 due to the circumstance that on the breaking up of organic substances which 

 contain it, it is given off as ammonia. If the ammonia is all collected and 

 estimated, the amount of nitrogen can be easily calculated. Kjeldahl's 

 method for carrying out this quantitative analysis is described in the Appendix. 

 The following exercises, however, are qualitative only. 



