DETECTION OF 'ACIDS. 401 



TABLE XIV. Substances insoluble or very difficultly soluble in water. 



A. When the substance is 

 soluble in cold or hot, dilute 

 or strong hydrochloric acid: 



Note. It Pb, Hg(ous), 

 Ag, are indicated by the 

 preliminary examination, 

 omit treatment with HC1, 

 but use HNO 3 . 



. Note whether the 

 effects are the same as in 

 Table XIII, B, 7, a and b. 

 Make tests for the acids 

 indicated there. 



b. If chlorine is given 

 off, a peroxide is present, 

 as MnO 2 , PbO ? , BaO 2 , etc., 

 or chromate (high color) . 



c. If no change takes 

 place except solution 



1. Subnitrate (or sub- 

 chloride) is suspected if Bi 

 or Sb is found as metal. 

 Boil substance in slight ex- 

 cess Na 2 CO s , filter, neutral- 

 ize filtrate and test for the 

 acid. 



2. Test for phosphate by 

 molybdate solution. 



3. Test for borate by al- 

 cohol flame. 



4. Arsenate and arsenite 

 are detected in analysis for 

 metals: make further tests 

 to distinguish the two. 



5. If no acid is found 

 and the substance is alka- 

 line, it is CaO or Ca(OH) 2 ; 

 if neutral, it is an oxide, as 

 ZnO, MgO, PbO, etc., or 

 their hydroxides. 



d. Effervescence and in- 

 flammable gas indicate a 

 free metal, as Zn, Fe, Sn, 

 etc. 



7>. When the substance is 

 insoluble or difficultly soluble 

 in hydrochloric, but soluble in 

 cold or hot, dilute or strong 

 nitric acid : 



a. Brown vapors and a 

 precipitate of sulphur indi- 

 cate a sulphide. 



6. Brown vapors alone 

 indicate free metal, as Ag, 

 Pb, Hg, Bi, Cu, etc. 



c. If the substance is 

 white, volatile on foil by 

 heat, turns black with 

 XII 4 OH, and soluble in 

 HNO 3 on long boiling, it 

 is likely HgCl or HgBr. 

 Test for the acid by boiling 

 some with dilute NaOH, 

 filter, acidify filtrate with 

 HNO S and add AgNO 3 . 



(Likewise for Hgl and 

 HgI 2 , which are yellow and 

 red respectively.) 



d. If no change except 

 solution, the substance is 

 likely an oxide or hydrox- 

 ide. This will also be indi- 

 cated by the metal present 

 and the appearance of the 

 compound. 



C. When the substance is 

 insoluble in either hydro- 

 chloric or nitric, but is solu- 

 ble in a mixture of the acids : 



It may be 



a. Mercuric sulphide, 

 HgS, black or red, and 

 volatile on foil by heat. 



b. Gold. 



c. Mercurous chloride, 

 HgCl. (Slowly soluble in 

 HNO 3 . See E, c.} 



d. A few sulphides and 

 oxides. 



D. When the substance is 

 insoluble in all acids : 



It may be 



a. Sulphate of Ba, Sr, 

 Pb. These must be fused 

 with Na 2 CO 3 . 



6. Lead chloride, PbCl 2 

 (PbBr 2 , PbI 2 ) (if not re- 

 moved by much hot water.) 



c. Chloride, bromide, 

 iodide, or cyanide of silver, 

 AgCl, AgBr, Agl, AgCN. 

 Test solubility in XH 4 OH 

 and Na 2 S 2 O 3 . 



(AgCN with HC1 forms 

 insoluble AgCl and leaves 

 HCN in solution recognized 

 by odor.) 



d. Silicic acid and most 

 silicates, native A1 2 O H , 

 Cr 2 O 3 , SnO 2 , CaF 2 . 



