590 MINERALOGY 



Illustration. Use fluorite, CaF 2 , for a, and for 6 use topaz. 



Phosphorus, P. Atomic weight, 31.04. Fusing point, 44.2 C. 



a. Flame coloration. Phosphates when heated in fine powder 

 on wire, then moistened with concentrated sulphuric acid, and 

 heated gently .until most of the white fumes of SO 3 are driven off, 

 then held at the tip of the blue cone of an O. F., yield a yellowish 

 green flame. The flame appears only momentarily and may be 

 easily overlooked. The charge must be moistened with acid again 

 and headed, when the flame will reappear. Sulphuric acid liberates 

 the phosphoric acid, which volatilizes, coloring the flame. 



6. Wet test. The powdered mineral is dissolved in nitric acid ; 

 if not soluble, it is first fused with 4 parts soda, then dissolved. 

 10 cc t of ammonium molybdate solution are heated in another test 

 tube to boiling, then the nitric acid solution of the mineral is poured 

 into the molybdate, and well shaken. If phosphoric acid is present, 

 a canary-yellow precipitate of ammonium phosphomolybdate, 

 (NH 4 ) 3 PO 4 , 12 MoO 3 . n (H 2 O), will form. This yellow precipitate 

 is very soluble in alkalies. Arsenic will yield a similar yellow pre- 

 cipitate, but only upon heating the solution above 80 C. 



Illustration. Use apatite, Ca 4 CaF(PO 4 )3. 



Nitrogen, N. Atomic weight, 14.04. Fusing point, 210 C. 



a. Closed tube test. The powdered mineral is fused in the closed 

 tube with 2 parts of potassium bisulphate, when nitrogen will be 

 liberated as red fumes, NO 2 , best observed by looking down in the 

 open end of the tube. 



6. Wet test. The substance is dissolved in sulphuric acid (one 

 of water to one of acid) and allowed to cool. Holding the tube in a 

 slanting position, a concentrated solution of ferrous sulphate is 

 poured in, so as to form a layer above the solution to be tested, and 

 not mix with it. If nitrates are present, a brown ring will form 

 where the two solutions are slightly mixed on contact. 



Illustration. Use niter, KNO 3 . 



Carbon, C. Atomic weight, 12. Infusible. 



a. Carbonates. 3 or 4 cc. of dilute hydrochloric or nitric 

 acid are heated in a test tube and several small fragments of the 

 mineral to be tested are dropped in the hot acid ; if carbonates are 

 present, they will be decomposed with effervescence. Minerals 

 are apt to contain a small amount of carbonates as impurities ; in 

 such cases the effervescence continues for a short time only ; where 

 the mineral is a pure carbonate, effervescence should continue until 

 the mineral has completely dissolved. Carbon dioxide, CO 2 , is 



