510 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



Fluorine, F = 19. 



Fluorine is found in the bones and teeth, in muscle, brain, blood, and in 

 all investigated tissues of the body, though in minute quantities. In one liter 

 of milk 0.0003 gram of fluorine have been detected. 1 Fluorine is found in 

 plants, and in soil without fluorine plants do not flourish. It seems to be a 

 necessary constituent of protoplasm. Free fluorine is a gas which cannot be 

 preserved, as it unite- with any vessel in which it is prepared. 



Hydrofluoric Acid, 1II\ is prepared by heating a fluoride with concentrated sul- 

 phuric acid, in a platinum or lead dish. 



CaF,+ H a S0 4 = CaS0 4 + 2HF. 



Properties. — Hydrofluoric acid is a colorless gas, so powerfully corrosive that breathing 

 its fumes results fatally. Its aqueous solutions are stable, but can be kept only in vessels 

 of platinum, gold, lead, or india-rubber. It etches glass, uniting to form volatile silicon 

 fluoride, 



Si0 2 + 4HF = SiF 4 -f-2H 2 0. 



Circulation in the Body. — Tappeiner and Brandl 2 have shown, on 

 feeding sodium fluoride (NaF) to a dog in doses varying between 0.1 and 

 1 gram daily, that the fluorine fed was not all recoverable in the urine and 

 feces, but was partially stored in the body. On subsequently killing the dog, 

 fluorine was found in all the organs investigated, and was especially found in 

 the dry skeletal ash to the extent of 5.19 per cent, reckoned as sodium fluoride. 

 From the microscopic appearance of the crystals seen deposited in the bone, the 

 presence of calcium fluoride was concluded. In this form it normally occurs 

 iu bones and teeth. 



Nitrogen, N = 14. 



Free nitrogen constitutes 79 per cent, of the volume of atmospheric air. It 

 is found dissolved in the fluids and tissues of the body to about the same extent 

 as distilled water would dissolve it. It is swallowed with the food, may par- 

 tially diffuse through the mucous membrane of the intestinal tract, but forms 

 a considerable constituent of any final intestinal gas. It is found in the atmos- 

 phere combined as ammonium nitrate and nitrite, which are useful in furnish- 

 ing the roots of the plant with material from which to build up proteid. 

 Bacteria upon the roots of certain vegetables combine and assimilate the free 

 nitrogen (.ft he air (Hellriegel and Willforth). Cultures of alga do the same. 3 



Preparation. — (1) By abstraction of oxygen from air through burning phosphorus in 

 a bell jar over water, pentoxide of phosphorus being formed, which dissolves in the water 

 and almost pure nitrogen remains. 



_• By heating nitrite of ammonium, 



NH 4 NO, = 2N+-2B O. 



Properties. — Nitrogen is especially distinguished by the absence of chemical 

 affinity for other element-. It does not support combustion, and in it both a 



1 i i. Tammann : Zeitschrifi fiir physiologiseht Chemie, 1888, Bd. 12, S. 322. 



5 ZeUachrifi fur Biologic, 1892, Bd 28, S. 518. 



3 P. Kosaowitch : Botaniaehe Zeitung, L894, Jahrg. 50, S. 97. 



