CARBON. 99 



white, crystalline substance, which is sparingly soluble in cold water, 

 somewhat more soluble in alcohol and in glycerin ; it has but weak 

 acid properties. When heated to 100 C. (212 F.) it loses water, 

 and is converte'd into metaboric acid, HBO 2 , which when heated yet 

 higher is converted into tetraborio add, H 2 B 4 O 7 , from which borax, 

 Na 2 B 4 O 7 -f 10H 2 O, is derived. At a white heat boric acid loses all 

 water, and is converted into boron trioxide, B 2 O 3 



Boric acid is obtained by adding hydrochloric acid to a hot satur- 

 ated solution of borax, when boric acid separates on cooling. The 

 chemical change is this : 



Na 2 B 4 O 7 + 2HC1 + 5H 2 O = 4H 3 BO 3 + 2NaCl. 



Tests for boric acid and borates. 

 (Sodium borate, Na,B 4 O 7 .10H 2 O, may be used. 



1. Heat some borax on the loop of a platinum wire. Notice that 

 it swells up during the time that water is expelled, and then melts 

 into a transparent, colorless bead of fused borax. 



2. To a concentrated neutral solution of a borate add solution of 

 either calcium, barium, or silver. In either case white precipitates 

 of borates are formed, having the composition CaB 4 O 7 , BaB 4 O 7 , or 



3. Mix in a porcelain dish some borax with a few drops of sul- 

 phuric acid, pour upon the mixture some alcohol and ignite. The 

 flame has a seam or mantle of a green color, which is best seen by 

 repeatedly extinguishing and rckjn.dlkig vi^e alcolioL. A. borax bead 

 moistened with sulphuric acicf and heated in a flame also colors it green. 



4. To a warm saturated solution of ,a borage add, sprne hydrochloric 

 or sulphuric acid. On cocking, shining scales of boric acid separate. 



5. A solution of borax, even when acidulated with hydrochloric 

 acid, colors turmeric-paper brown, after this has been dried. 



QUESTIONS. 121. How is carbon found in nature? 122. State the physical 

 and chemical properties of carbon in its three allotropic modifications. 123. 

 Mention three different processes by which carbon dioxide is generated in 

 nature, and some processes by which it is generated by artificial means. 124. 

 State the physical and chemical properties of carbon dioxide. 125. Explain 

 the process of respiration from a chemical point of view. 126. What is the 

 percentage of carbon dioxide in atmospheric air, and why does its amount not 

 increase? 127. State the composition of carbonic acid and of a carbonate. 

 How can they be recognized by analytical methods? 128. Under what circum- 

 stances will carbon monoxide form, and how does it act when inhaled ? 129. 

 What is destructive distillation, and what gases are generally formed during 

 that process? 130. Explain the structure and luminosity of flames. 



