422 PHOSPHORIC ACID. 



of plates, extricated a considerable quantity of phosphuretted hydro- 

 gen^ and caused the phosphorus to become of a deep red brown color. 

 It is not, however, considered as certain that hydrogen is contained 

 in phosphorus ; it may, in this case, have proceeded from moisture 

 accidentally present, for a little moisture would afford a large vol- 

 ume of hydrogen gas, which would of course be phosphorized. 



5. POLARITY. Phosphorus is attracted by the negative pole in the 

 galvanic circuit, and is therefore electro-positive. 



6. COMBINING WEIGHT, 12. 



7. MISCELLANEOUS. Phosphorus exists no where in nature in a 

 free state ; this would be impossible on account of its combustibility. 

 It is found in the acid of the natural phosphates of lead, copper, iron, 

 lime, &tc. ; most abundantly, however, in animal bodies, and more 

 particularly in bones. It exists also in the saline form, in vegetable 

 fluids. Phosphorus is little used except in the laboratory. It is a 

 violent poison, even as is said, in the dose of 1 grain. In more 

 moderate doses, it is stimulating, antispasmodic, &c. Its best form 

 of exhibition is, dissolved in ether, 8 grs. to 1 oz. of which 4 or 5 

 drops containing about T V of a gr. may be given two, three, or 

 more times in a day, in some spirituous tincture. Coxe. 



PHOSPHORIC ACID. 



1. HISTORY. Not known till after the discovery of phosphorus; 

 observed by Boyle ; first examined by Margraff. 



2. PREPARATION. 



(a.) By decomposing bone ashes by sulphuric acid, for the particu- 

 lars of which process, see phosphate of lime. 



(b.) By the combustion of phosphorus. Phosphorus burning in an 

 earthen dish floating on mercury is covered by a bell glass full of 

 common air or oxygen gas.* The combustion in the latter, is rapid 

 and brilliant, with much heat and light ; the phosphorus with the oxy- 

 gen is converted into phosphoric acid, which, jn a diy vessel, is con- 

 densed in white flakes ; the gas, if pure and in proper proportion, 

 wholly disappears, and any foreign gas remains. There should be 

 an excess of oxygen gas, to save the vessels from fracture ; if the 

 oxygen is pure at first, the remaining gas is still so. 



* 500 grs. of phosphorus require 1 cubic foot of oxygen gas at a medium tempera- 

 ture for saturation, and the product is 1250 grs. dry phosphoric acid; 1 grain of phos- 

 phorus requires 15 cubic inches of common air, and of course about 4 cubic inches of 

 oxygen for its saturation. Note Book. Dr. Hope's Lectures, Edinb. 



