CHAPTER XVI 



Oxids of Carbon, Carbonates, and Carbon Com- 

 pounds 



127. Carbon Dioxid. Carbon dioxid is obtained from 

 the combustion of carbon and also from the treatment of 

 a carbonate with an acid. A carbonate is a salt of car- 

 bonic acid, M 2 CO 3 , in which M represents any mono- 

 valent metal, as K or Na. Calcium carbonate, CaCO 3 , is 

 the most abundant carbonate found in nature. When a 

 carbonate is treated with an acid CO 2 is liberated, and a 

 salt is formed, as 



CaC0 3 + 2HC1 = CaCl 2 + CO 2 + H 2 O. 



Experiment 24. Preparation of carbon dioxid. Arrange the 

 apparatus as for the preparation of hydrogen. Put 10 grams of 

 marble, CaCO 3 , into the Woulff bottle, and sufficient water to 

 cover the end of the thistle tube. Fill 2 or 3 cylinders with water 

 for collecting the gas, which is only slightly soluble in water, then 

 add slowly, through the thistle tube, about 20 cc. concentrated 

 HC1. Allow a little of the first gas generated to escape into the 

 room and then collect 2 or 3 cylinders of CO 2 . Remove the cylinders 

 from the pneumatic trough and place them on the desk, right side 

 up. Now remove the delivery tube from the pneumatic trough 

 and allow the gas to pass into a test-tube containing about 10 cc. of 

 clear lime water, Ca(OH) 2 . If necessary, add through the thistle 

 tube a little more acid to the generator. Observe the white precipi- 

 tate formed in the test-tube. Let the gas pass through the lime 

 water for several minutes, until the solution becomes clear. Now 

 boil the solution and observe the reappearance of the white precipi- 

 tate. Test some of the escaping gas with a burning splinter. 

 Pour a receiver of the gas over a candle or a low gas flame, and 

 observe the result. Thrust a burning splinter into a cylinder of 



