CHAPTER II 



DETECTION OP THE ELEMENTS AND OF 

 INORGANIC SALTS 



The body tissues, foodstuffs, etc., are made up of a large 

 number of elements which are seldom free, but usually com- 

 bined in the form of organic substances or inorganic salts. The 

 latter are often in more or less firm combination with the or- 

 ganic constituents of the tissues. The inorganic materials often, 

 but not always, can be extracted from tissue material with water 

 or dilute acid. To detect the elements in organic substances it 

 is usually necessary to destroy the organic material by fusing 

 it with an oxidizing agent. Metals -or salts making up part of 

 the compound are set free in this manner and can be detected by 

 the usual qualitative tests. The following experiments will 

 demonstrate the presence of the various elements and salts 

 which are found most frequently in the body or in food 

 materials. 



1. 1. Carbon. Place a small quantity of sugar, fat, dry 

 casein or meat which has been thoroughly dried and ground up 

 in a test tube and heat in the Bunsen flame. The material is 

 decomposed, leaving a black residue of carbon. 



2. Hydrogen. Observe the liquid which condenses on the 

 inside of the test tube. This is water. Since the original mate- 

 rial was dry, this water must have been formed from the 

 hydrogen in the substance, and oxygen from the substance itself 

 or the air. 



3. Oxygen. There is no simple method for detecting the 

 presence of oxygen in combination. In analysis, the sum of all 

 the other constituents present in a given substance is subtracted 

 from the weight of material used. The difference is taken as the 

 amount of oxygen in the compound. 



210 



