QUESTIONS AND ANSWERS 5 



A tribasic acid is one having three replaceable atoms of hydrogen 

 in its molecule, as phosphoric acid, HgPO^. 



Define crith, atomic weight, Jind molecular weight. 



A crith is the unit of weight for gases, it being the weight, in a 

 vacuum, of a litre of hydrogen gas at 0° C. A crith = 0.0899 gramme. 



Atomic weight is the weight of an atom of a substance compared 

 with the weight of an atom of hydrogen which is taken as unity. 

 (In scientific work, oxygen is taken as the standard, but the U. S. P. 

 takes hydrogen.) 



Molecular weight is the sum of the atomic weights of the element 

 or elements contained in a molecule of a substance. 



Define allotropism and reduction. 



AUotropism is the property possessed by certain elements of 

 presenting themselves in two or more dififerent forms, as the aUo- 

 tropic forms of carbon, seen in the diamond, charcoal and graphite. 



Reduction is the process of abstracting oxygen from an oxide. 

 (This is a generally accepted definition, although the subject of 

 reduction has a deeper significance, as may be instanced in the 

 reduction of calomel with stannous chloride, which also involves 

 the subject of valence. SnClj + 2HgCl = SnCl4 + Hg^. See oxi- 

 dation, p. 16.) 



What is a metal? 



A metal is an element which is predominantly basic in its chemi- 

 cal behavior. Metals are solid at ordinary temperature, except 

 mercury, usually opaque, have a more or less metallic lustre, are 

 malleable, ductile, tenacious, good conductors of heat and elec- 

 tricity, and are capable of forming basic substances and salts. 



What is meant by isomerism? 



Two or more compounds which contain the same elements in the 

 same relative proportions by weight in the molecule, but differ more 

 or less widely in their physical, chemical and physiological proper- 

 ties, are called isomeric, e.g., C3H0O3, lactic acid, and CeHj^Oe, 

 grape sugar. 



Define chemical action. Name three kinds and give an example of 

 each. 



Chemical action refers to the changes taking place in two or 

 more elements when brought in contact or disintegrated. 



Light : Silver chloride decomposes in the presence of light. 

 ^ - Heat : Heat decomposes red oxide of mercury into mercury and 

 ; oxygen. ^ »;, ^^ j ^ ., , 





