QUESTIONS AND ANSWERS 25 



Describe an efHcient method of disinfecting by the use of formaldehyde. 

 For every 1000 cubic feet of air space, mix in a deep vessel 16% 

 ounces of potassium permanganate with 20 ounces of formalin 

 (a 40 per cent, aqueous solution of formaldehyde). Close all open- 

 ings and leave this mixture in the room for 3 hours before opening. 



PHOSPHOEUS ^ 



Give a description of phosphorus as to (a) occurrence, (b) physical 

 properties, (c) source. 



(a) Never found free in nature, but as phosphates is an im- 

 portant constituent of plants, animals and the earth's crust. 



(b) Phosphorus exists in several aUotropic varieties, the more 

 important of which are the yeUow and red. The yellow variety is a 

 yeUowish-white, waxy solid of specific gravity 1.837. It melts at 

 44.2° C. and boils at 263° C. ; is highly inflammable and oxidizes 

 readily in the air at ordinary temperature. It has a faint odor, 

 resembling garlic, is very poisonous, is Soluble in carbon disul- 

 phide and insoluble in water. The red variety is not easily inflam- 

 mable in air, has a density of 2.2, is insoluble in carbon disulphide 

 and is not poisonous. 



(c) Prepared from bone-ash or from sombrerite, an impure cal- 

 cimn phosphate found in the West Indian guano. 



Mention the principal uses of phosphorus. 



Used in matches, vermin poison, medicine and fertilizers. 



Give (a) the symbol, (b) the valence, (c) atomic weight, (d) molecular 

 weight, of phosphorus, 

 (a) P, (b) 3 and 5, (c) 31, (d) 124. 



Name the aUotropic forms of phosphorus. 

 Yellow, red, white and black. 



HALOGENS 



Name the elements of the halogen group and write the symbol of each. 

 Fluorine, F ; chlorine, CI ; bromine, Br ; iodine, I. 



Give the physical and chemical properties of iodine. Describe a test 



* for iodine. 



Iodine is a bluish-black crystalline substance, with a metallic 

 luster and an odor faintly resembling that of chlorine. Its specific 

 gravity is 4.95 and its atomic weight is 125.89. Its vapor has a violet 

 color. Iodine is almost insoluble in water but forms several im- 

 portant compounds with other elements. 



