ULTIMATE CONSTITUENTS OF THE BODY. 83 



binary compounds into one substance, as the carbonate of soda or the 

 phosphate of lime. 



If the oxygen and the nitrogen, which seem to exist free in the 

 blood and other fluids, be really only dissolved in them, they afford 

 examples of a simple element entering as such into the composition of 

 the body ; but it is possible that these gases are in some unknown 

 though loose state of chemical combination in those fluids. 



The carbonic acid gas is, however, a binary compound, consisting 

 of one atom of carbon and two atoms of oxygen (C0 2 , carbonic acid). 

 Again, the water is composed of two atoms of hydrogen and one atom 

 of oxygen, chemically combined as an oxide of hydrogen (H 2 0, hydric 

 oxide). The chloride of sodium (common salt) consists of one atom 

 of chlorine united with one atom of sodium (NaCl, sodic chloride) ; 

 chloride of potassium, of chlorine and potassium (KC1, potassic chlo- 

 ride); fluoride of calcium (fluorspar) consists of two atoms of fluorine 

 and one of calcium (CaF 2 , calcic fluoride). The alkalies, soda and 

 potash, and the earths, lime and magnesia, are the oxides of the 

 metals sodium, potassium, calcium, and magnesium, that is, are com- 

 pounds each of one atom of oxygen with one or two atoms of those 

 metals respectively (Na 2 0, K 2 0, CaO, and MgO, sodic, potassic, calcic 

 and magnesic oxides). All the preceding bodies are binary compounds; 

 but as examples of substances in the body, which appear to be formed 

 by the union of two such binary compounds, we may mention the 

 phosphates, sulphates, and carbonates of soda, potash, lime, and mag- 

 nesia (otherwise named, the sodic, potassic, calcic, and magnesic phos- 

 phates, sulphates, and carbonates), which may be regarded as com- 

 pounds of phosphoric, sulphuric, and carbonic acids with the above- 

 mentioned alkalies and earths, carbonic acid being itself composed, 

 as already stated, of one atom of carbon and two atoms of oxygen 

 (C0 2 ) ; sulphuric acid, of one atom of the well-known substance 

 sulphur, and three atoms of oxygen (S0 3 ); and phosphoric acid of two 

 atoms of phosphorus and five atoms of oxygen (P 2 5 ). The trace of 

 silica or flint, found in the body, is an oxide of the metal silicon (Si0 2 , 

 silicic acid). The small but essential quantity of the metal iron (Fe) 

 exists also in some combined state; and the minute traces of the 

 metals manganese (Mn) and copper (Cu), and of alumina, the basis of 

 clay, which is an oxide of the metal of aluminium (A1 2 3 ), are perhaps 

 accidental. 



But the organic proximate constituents of the body have a much 

 more complex chemical composition, though they too are resolvable 

 by spontaneous decomposition, by chemical reactions, or by the de- 

 structive action of fire, into a few ultimate elements, which then revert 

 to the inorganic state. The simplest of these organic constituents are 

 ternary compounds, that is, they are formed by the combination of 

 three chemical elementary substances ; whilst others are quaternary, 

 or even quinary compounds. 



