( II1-AIK Al. PRELIMINARIES 



carbonic acid. Hydrochloric acid occurs in the stomach. 

 It is the only inorganic acid that is found free in the body. 



Salts are compounds formed from an acid when the whole 

 or part of the hydrogen of the acid is replaced by a metallic 

 clement or group of elements. Common salt is a salt formed 

 from hydrochloric acid by replacing the hydrogen of the acid 

 by the metal sodium, and is named sodium chloride (NaCl). 

 Plaster of 1'aris is a salt formed from sulphuric acid by re- 

 placing the hydrogen by the metal calcium, and is named 

 calcium sulphate, or sulphate of lime (CaSO 4 ). Common soda 

 is a salt formed from carbonic acid by replacing the hydrogen 

 by the metal sodium, and is named sodium carbonate (Na.,CO. ( ). 

 Bone ash consists chiefly of a salt of lime formed by replacing 

 the hydrogen of phosphoric acid by the metal calcium, and is 

 named calcium phosphate, or phosphate of lime (Ca 3 F. 2 O 8 ). 



The chief salts found in the body are : sodium chloride, 

 sodium carbonate, sodium phosphate, and in a smaller amount 

 the corresponding salts of potassium ; the sulphates of sodium 

 and potassium, calcium carbonate (CaCO.j), the phosphates of 

 calcium and of magnesium, and some salts of iron. 



When the body of an animal is burnt the ashes consist of 

 the salts of the body, the phosphate and carbonate of calcium 

 being present in by far the largest amount. 



The organic compounds of the body belong to the following 

 groups :- - 



Proteids, which consist of carbon, hydrogen, oxygen, 

 and nitrogen, united together in certain proportions with a 

 small amount of sulphur. Albumin, fibrin, are examples of 

 proteids. (They will be considered under Food.} 



Carbohydrates, which consist of carbon, hydrogen, and 

 oxygen united in certain proportions, but always containing 

 twice as many parts of hydrogen as of oxygen. Sugar is an 

 example of a carbohydrate. 



Fats, which consist of carbon, hydrogen, and oxygen united 

 in certain proportions, but always containing more than twice 

 as many parts of hydrogen as of oxygen. 



There arc also present some organic acids and salts and 

 many other organic compounds, of which important ones are 

 urea (CON,H 4 ) and uric acid (C H 4 N 4 O.,). (These will be 

 considered under Urine.) 



