184 OUTLINE OF CHEMICAL STUDY 



210. Acids. An acid is a compound made up of 

 hydrogen and a negative element or radical. Note these 

 symbols of acids : HC1, hydrochloric; HBr, hydrobro- 

 mic; HNO 3 , nitric; H 2 SO 4 , sulphuric. Acids generally 

 have a sharp or rather sour taste ; they often act upon 

 other compounds, causing chemical changes; some 

 acids act strongly upon animal matter, and some are 

 poisonous. 



The sharp taste of many fruits is due to acids. Lem- 

 ons, raspberries, and currants contain citric acid ; grapes 

 contain tartaric acid; apples and cherries, malic acid. 

 Vinegar owes its sour taste to acetic acid, and sour milk 

 contains lactic acid. 



211. Bases. A base is composed of OH in combina- 

 tion with a positive element or radical. OH is a neg- 

 ative radical ; it is sometimes called hydroxyl. 



Four bases are common: NaOH, sodium hydrate; 

 KOH, potassium hydrate; Ca(OH) 2 , calcium hydrate; 

 NH 4 OH, ammonium hydrate. The last of these, NH 4 OH, 

 is diluted with water and used for household purposes 

 under the name ammonia. NaOH and KOH are used 

 in making soap. Ca(OH) 2 is sometimes used in making 

 other bases. 



An alkali is a base that is soluble (can be dissolved) 

 in water. The strongly basic compounds NH 4 OH, 

 NaOH, and KOH are alkalis. 



212. Metals. The positive or base-forming ele- 

 ments are commonly called metals. We usually think 

 of a metal as a solid, heavy, and rather hard substance. 

 These properties are true of some metals, but not of all ; 



