IN POPULAR CHEMISTRY. 87 



6. State the formula? of niter, saleratus, carbonate and 

 bicarbonate of soda, plaster, pearlash, saltpeter, plaster of 

 Paris, gypsum, carbonate and bicarbonate of potash, sal- 

 soda, and soda. 



Niter, saltpeter 



Saleratus, pearlash ........................................ HKCO 3 . 



Carbonate of soda, sal-soda .............................. Na 2 CO 3 . 



Bicarbonate of soda, " soda " ............................ H3STaCO 3 . 



Plaster, gypsum ........................................... CaSO,2H 2 O. 



Plaster of Paris ........................................... CaSO 4 . 



7. Explain hoiv ammonium carbonate is formed in the 

 process of maMng coal-gas. 



Nitrogen exists in small quantities in coal, and when that 

 is distilled at a high temperature, the elements in their nascent 

 state combine to form this compound. 



8. Upon what fact depends the formation of stalactites ? 



Water containing carbonic acid in solution will dissolve car- 

 bonate of lime freely, but when, on exposure to the air, the 

 gas escapes, the carbonate is deposited. 



9. iniy is HF kept in gutta-percha bottles ? 



Because it will dissolve silica, and so destroy a glass bottle. 



10. Explain the use of borax in washing. 



It softens "hard" water by uniting with the soluble salts 

 of lime or magnesia, and making insoluble ones which settle 

 and form a thin sediment in the bottom of pitchers in which it 

 is placed. 



11. How are petrifactions formed ? 



Certain springs contain large quantities of some alkaline 

 carbonate ; their waters, therefore, dissolve silica abundantly. 

 If we place a bit of wood in them, as fast as it decays, parti- 



it will be seen that the above slag contains nearly g^th of its weight, in a 

 form which would be easily rendered available for plants by the combined 

 action of air and moisture. When the slag is run into water, or blown 

 into a frothy condition by the blast, it resembles pumice-stone, and is easily 

 ground to a powder fit for applying to the soil. 



