296 PROCEEDINGS OF THE AMERICAN ACADEMY 



depends on the presence of an excess of silicic acid. The solution 

 containing nitrites is delicately balanced, but it is always adapted to the 

 statical determination of phosphoric acid by the magnesia mixture, or 

 its estimation volumetrically, in using uranic nitrate. The quantity 

 of phosi^horic acid pi-esent in mineral or artificial forms of compounds 

 can thus be accurately obtained, and the most compact aggregates do 

 not resist solution. 



WIDE DISTRIBUTION OF PHOSPHORUS. 



In applying this mode of analysis to a great variety of rocks, it 

 soon became evident that phosphoric acid is widely distributed. In 

 some cases, the basis, as well as the cementing part, of a rock contained 

 it, so that adherence to the j^lan of seeking it in classified rocks was not 

 possible. Associated with silicates of the moi-e basic earths and the 

 protoxides of metals, it is found in all the clays, the new and old lavas, 

 trachytes, slates, — from the most fissile to the most compact, — shales, 

 ashes of coals ; in the rocks formed of quartz, feldspar, and mica ; in 

 aggregates where feldspar is replaced by quartzite, and in those con- 

 taining chlorite. The well-known conglomerates of Roxbury, and a 

 silicious slate reposing near it, contain phosphates. 



In the opaque feldspars, the ancient porphyries of Rome and Carthage, 

 phosi)hates occur ; but the glassy and rose-colored varieties have not af- 

 forded it. The lepidolite of Paris, Me., contains it ; furnace products, 

 slags from copper and zinc, afford it. This list might be extended, without 

 indicating any law relating to the affinities, which may perhaps be dis- 

 covered as the observations are multiplied. We have iu phosphatic salts 

 in rocks another consolidating material, and an element of change. 



VANADIUM ASSOCIATED WITH PHOSPHORUS. 



In many of the analyses made after tlie method described, another 

 acid was found associated with phosphoric acid, and this was easily 

 proved to be a compound of vanadium. The frequency of its occur- 

 rence as acid or oxide, its well-marked characters as a changeful body, 

 the colors of its compounds and mixtures, give great interest to this 

 discovery. Owing to its association with proto salts of manganese and 

 iron in rocks, it proves to be active, first as a binding, and secondly 

 as a disintegrating, agent. It is a matter of surprise that the dissemina- 

 tion of vanadium has not before been noted, especially since its later 

 classification with phosphorus leads to such a conclusion. 



When the rocks treated by the above method for phosphoric acid 

 contain manganic compounds, if the second filtrate, balanced by am- 



