CLASSIFICATION OF MINERALS. 71 



Tin-foil is used to fuse with certain peroxyds of metals to 

 reduce them to protoxyds. The assay, previously heated in 

 the reducing flame, should be touched with the end of the 

 tin foil ; a very minute quantity of a metallic oxyd is thus 

 detected. 



Saltpeter added along with a flux to a compound contain- 

 ing manganese, gives the amethystine color, when the quan- 

 tity is too small to be detected without it. 



Potash sails, if there is no soda present, give a slightly 

 violet tinge to the flame. 



Soda salts give the flame a deep yellow color. 



Lithia salts give the flame a reddish tinge ; the silicate 

 require the addition of some fluor spar and bisulphate of pot- 

 ash. By adding soda and heating on platinum, the lithia 

 stains the platinum brown. 



Sulphurets, Sulphates. A glass made of soda and silica 

 becomes red or orange yellow when sulphur is present. 

 Heated on charcoal with soda, and then adding a drop of 

 water, they yield sulphuretted hydrogen, which blackens a 

 test paper containing acetate of lead. Sulphurets heated in 

 a glass tube closed below, with litmus paper above, redden 

 the litmus paper, and yield usually a sulphureous odor. 



Seleniets give off a horse-radish odor. 



Arseniurets give off an odor like garlic, which is brought 

 out by heating with soda in the reduction flame, if not other- 

 wise perceptible ; heated in a tube, orpiment is condensed. 



Fluorids. Heated with salt of phosphorus, previously 

 melted in a glass tube, the glass is corroded ; and Brazil 

 paper placed in the tube becomes yellow. The salt of 

 phosphorus for this trial should be free from all chlorids. 



Nitrates detonate on burning coals. 



CHAP. V.— CLASSIFICATION OF MINERALS. 



Under the term mineral, as explained, are included all 

 inorganic substances occurring in nature. These substan- 

 ces have been found to consist of various elements, some few 



How and for what is tin-foil used ? saltpeter? — What is said of the 

 constitution of minerals? 



* For full information on the use of the blowpipe and its reactions 

 there is no better work than Berzelius on " the Use of the Blowpipe,'*' 

 translated by J. O. Whitney. 238 pp. 8vo. Boston, 1845. 



