CHLORINE. 117 



Hydrogen phosphide corresponds to the analogous composition of ammonia, 

 NH 3 . While the latter is readily soluble in water, and has strong basic prop- 

 erties, hydrogen phosphide is but sparingly soluble in water, and its basic prop- 

 erties are very weak. However, a few salts, such as the phosphonium chloride, 

 PH 4 C1, analogous to ammonium chloride, NH 4 C1, are known. 



16. CHLORINE. 



Cli = 35.4 (35.37). 



Haloids or Halogens. The four elements, fluorine, chlorine, 

 bromine, and iodine, which form a natural group of elements, are 

 known as haloids^ or halogens. The relation shown by the atomic 

 weights of tMse four elements has been mentioned in connection with 

 the consideration of natural groups of elements generally (see page 

 63). In many other respects a resemblance or relation can be dis- 

 covered. For instance : All haloids are ipiixalejit -.elements, they 

 combine with hydrogen, forming the acids HF, HC1, HBr, HI ; they 

 combine directly with most metals, forming fluorides, chlorides, 

 bromides, and iodides. The relative combining energy lessens as the 

 atomic weight increases ; fluorine with the lowest atomic weight hav- 

 ing the greatest, iodine with the highest atomic weight the smallest, 

 affinity for other elements. The first two members of the group are 

 gases, the third (bromine) is a liquid, the last (iodine) 'a solid, at 

 ordinary temperature. They all show a distinct color in the gaseous 

 state, feave a disagreeable odor, and possess disinfecting properties. 



Occurrence in nature. Chlorine is found chiefly as sodium 

 chloride or common salt, NaCl, either dissolved in water (small 

 quantities in almost every spring water, larger quantities in some 

 mineral waters, and the principal amount in sea- water), or as solid 

 deposits in the interior of the earth as rock salt. 



QUESTIONS. 141. In what forms of combination is phosphorus found in 

 nature ? 142. Give an outline of the process for manufacturing phosphorus. 

 143. What are the symbol, valence, atomic and molecular weights of phos- 

 phorus ? 144. State the chemical and physical properties both of common and 

 red phosphorus. 145. By what methods may phosphorus be detected in cases 

 of poisoning? 146. What two oxides of phosphorus are known; what is their 

 composition, and what four acids do they form by combining with water ? 147. 

 State the official process for making phosphoric acid, and what are its proper- 

 ties? 148. By what tests may the three phosphoric acids be recognized and 

 distinguished from phosphorous acid ? 149. What is a phosphide, phosphite, 

 phosphate, and hypophosphite? 150. What is glacial phosphoric acid, and in 

 what respect does its action upon the animal system differ from the action of 

 common phosphoric acid. 



