DESCRIPTION OF Till. INSTIM'Ml.NTS 



colorless Mini odorless, which distinguishes it from other gases which 

 may l>e yielded in dissolving a mineral in arid-. A direct test 

 may lie Mpplied ly holding a glass rod down in the test tube during 

 the elYervescenee, on the end of which a drop of lime water is 

 suspended. The drop will soon appear milky from the formation 

 of cMlcium carbonate. 



6. Organic carbon. Carbon in organic matter is detected by 

 heating the substance in a closed tube, when it will blacken, and 

 generally yields an empyreumatic odor, also sometimes an oily 

 distillate. 



c. Free carbon, as coal or graphite, when heated on platinum foil, 

 glows, or burns, leaving an ash which is light in color. Diamond must 

 be powdered and heated to a high temperature before it burns. 



Illustration. For a use calcite, CaCOa, and for 6 any organic 

 acid, as oxalic, C 2 H 2 04, will do. 



Silicon, Si. Atomic weight, 28.4. Fusing point, 1200 C. 



a. Silica, Si0 2 , when heated in the S. Ph. bead, dissolves only 

 very slowly ; it yields therefore a translucent bead. If a fragment 

 of a silicate is heated in an S. Ph. bead, the bases or other oxides go 

 into solution, leaving the silica insoluble, in more or less of the same 

 shape as the fragment used. This is known as the silica skeleton. 



Illustration. Use a small fragment of orthoclase, KAlSisOg. 



6. Gelatinization. Numerous silicates when in fine powder are 

 decomposed by hydrochloric or nitric acid, and on evaporating 

 the solution nearly to dryness the silicic acid will separate and 

 appear as a jelly. Best observed by stirring with a platinum wire : 

 upon further evaporation to dryness the silicic acid is dehydrated. 

 If the dry residue is now moistened with a few drops of dilute HC1, 

 other elements are dissolved as chlorides, leaving the silica as a 

 white insoluble residue, which is filtered out, washed, and tested as 

 in a. 



Illustration. Use calamine, Zn 2 SiO 4 . 2 H 2 O. 



c. All silicates, when fused with 5 parts soda and dissolved in 

 dilute hydrochloric acid and evaporated as in 6, yield gelatinous 

 silica ; on evaporation to dryness the silica is separated and i 

 as in a. This is the method used in qualitative and quantitative 

 analysis to decompose silicates and separate silica from the bases. 

 All liases will be in the filtrate from the silica and may be detected 

 by appropriate tests. 



Illustration: Fuse powdered orthqclase with soda and separate 

 silica as described. 





