132 APPLIED SCIENCE 



however, from the other forces of gravitation, heat, light, 

 and electricity. 



When two elements or compounds act chemically upon 

 each other (disintegrate) or are treated in some special way, 

 they are generally altered in appearance and state. 



To illustrate: A mixture of oxygen and hydrogen is still a gas, 

 but a chemical compound of oxygen and hydrogen is water, or a 

 liquid. When zinc is added to muriatic acid ("raw acid") heat is 

 given off, a gas is generated, and the zinc combines with the acid. 

 The resulting compound, zinc chloride, is different from the original 

 substances. The equation is : 



Zn + 2HC1 ZnCl 2 + 2H 



Zinc Hydrochloric Zinc Hydrogei 



Acid Chloride 



These illustrations show that chemical action is distinguished 

 from all other action : first, by producing a compound with proper- 

 ties entirely changed from those of the substances or compounds, 

 originally used; second, by the fact that it takes place between 

 definite weights and volumes. 



140. Hydrogen. Hydrogen is a colorless, odorless gas, 

 burning with a pale blue flame and very little light, but with 

 great heat. It is chemically prepared by the action of zinc 

 or iron, and hydrochloric or sulphuric acid. Zinc and sul- 

 phuric acid form zinc sulphate and hydrogen. The reactions 

 may be represented by the equations: 



Zn + 

 Zinc 



Fe + 

 Iron 



