QUESTIONS AND PROBLEMS iig 



with another, what is usually the effect upon the melting point ? 

 Give an example. 

 29. Name some soft and some hard metals. How may the relative hard- 

 ness be roughly determined ? What is the effect of i per cent, of 

 carbon in iron upon its hardness, and how may steel be made 

 harder or less hard by " tempering " ? 



Combining Weights of the Elements. 



30. What evidence is there that the same compound always contains the 



same elements in the same proportions by weight ? Give 

 examples. 



31. What evidence is there that two elements can combine in two or 



more proportions? In this case is there any simple relation 

 between the proportions? 



32. What is meant by the "combining weights" of the elements, and 



with what are they compared as unity ? What are the combining 

 weights usually taken for hydrogen, oxygen, carbon, and mercury ? 



33. The proportion in which hydrogen and oxygen are combined in 



water is as i : 8, but the combining weight of oxygen is taken as 

 16 (hydrogen = 1). What number of combining weights then of 

 hydrogen and oxygen are combined together in water, and what 

 formula may be employed to express this shortly ? 



34. Carbon combines with oxygen to form carbonic acid gas in the pro- 



portion of 3 : 8. The combining weights of the elements are 12 

 and 16 respectively. Represent the composition of carbonic acid 

 gas by the simplest possible formula. 



35. What does the formula " HgO " mean both as to the elements of the 



compound and their quantities ? 



36. For what elements do the following symbols stand : C, Cu, Fe, H, 



Hg, Mg, Mn, N, Na, P, Pb, K, S, and Si ? 

 *37. Determine the proportions in which silver and oxygen are combined 

 together in the oxide of silver, after first drying in the water oven. 



Composition of the Basic Oxides and Hydrates. 



38. The composition of lime is expressed by the formula CaO ; calculate 



its percentage composition. 



39. From red lead 97.65 per cent, of its weight of litharge is obtained 



on heating. Litharge contains 7.2 per cent, of its weight of 

 oxygen. What are the simplest formulae that will represent the 

 composition of litharge and red lead ? 



