AMBi3R. 93 



sheets arc then sawn up of the size required. The pencil is 

 pure graphite, and the foliated variety is preferred on account 

 of its being freer from impurities. 



Graphite is extensively employed for diminishing the 

 friction of machinery ; also for the manufacture of crucibles 

 and furnaces, and as a wash for giving a gloss to iron stoves 

 and railings. For crucibles it is mixed with half its weight 

 of day. . 



CARBONIC ACID. ' 



Carbonic acid is the gas that gives briskness to the Sara- 

 toga and many other mineral waters, and to artificial soda 

 water. Its taste is slightly pungent. It extinguishes com- 

 bustion and destroys life. Composition : . carbon 27*65, 

 oxygen 72*35. 



Besides occurring in mineral waters, it is common about 

 some volcanoes. The Grotto del Cane (Dog cave) near 

 Naples, is a small cavern filled to the level of the en- 

 trance with this gas. It is a common amusement for the 

 traveler to witness its effects upon a dog kept for the purpose. 

 He is held in the gas a while and is then thrown out appa- 

 rently lifeless ; in a few minutes he recovers himself, picks 

 up his reward, a bit of meat, and runs off as lively as ever. 

 If continued in the carbonic acid gas a short time longer life 

 would have been extinct. 



Carbonic acid combined with lime forms carbonate of lime 

 or common limestone ; with oxyd of iron it constitutes spathic 

 iron, one of the common ores of iron ; with oxyd of zinc, it 

 forms calamine, the most profitable ore of zinc. It is found 

 in combination also in various other minerals. 



In irregular masses. Color yellow, sometimes brownish 

 or whitish; luster resinous. Transparent to translucent. 

 H = 2— 2*5. Gr = 1*18. Electric by friction. 



Composition. Carbon 79*0, hydrogen 10*6. oxygen 10*5 

 Burns with a yellow flame and aromatic odor. 



Obs. Occurs in alluvium and on coasts, in masses from 

 a very small size to that of a man's head. In the Royal 

 Museum at Berlin, there is a mass weighing 18 pounds. On 



For what other purposes is it used 1 What is carbonic acid ? Com- 

 bined with lime, what does it form 1 What is the appearance of amber ? 

 Where does it occur? 



