PROBLEMS OF CHEMISTRY 313 



are pleasant, and, indeed, useful. Before we can under- 

 stand, if we ever are to understand, the difference between 

 a living and a dead tissue, we must understand what 

 protoplasm is, and our chances of solving the problem pre- 

 sented by this important basis of life are extremely poor. 

 Still, we may hope to get nearer its solution by continued 

 investigation, and we shall have to be satisfied with small 

 returns for our labor. 



Chemistry has to deal with the composition of things, 

 and the changes in the composition of things, and all that 

 pertains to these subjects. Changes in composition are 

 often brought about by raising the temperature. To take 

 a comparatively simple, though not a familiar, example, 

 water is a compound of the elements hydrogen and oxygen. 

 When this is heated, it is converted into water-vapor. 

 When this vapor is heated to 4,500 degrees Fahrenheit, it 

 is resolved into hydrogen and oxygen. At this tempera- 

 ture the compound, water, cannot exist. On the other 

 hand, when hydrogen and oxygen are brought together at 

 ordinary temperatures, they do not combine to form water, 

 unless a spark or a flame is brought in contact with the 

 mixture, when a violent explosion occurs, and this is the sig- 

 nal of the chemical union of the two elements to form water. 

 Again, when wood is heated, it gives off gases and liquids, 

 and at last there is nothing left but charcoal, which is one 

 form of the element carbon. It is plain that some substances, 

 that can exist at ordinary temperature, are decomposed 

 that is to say, they cannot exist at high temperatures. This 

 is, in fact, true of many of the substances familiar to us. 

 But heat not only decomposes compounds ; it also, if not too 

 intense, causes elements to combine to form compounds. 

 In the laboratory and in the factory heat is constantly 

 being employed for the purpose of bringing about, or aid- 

 ing, chemical action. The blast-furnace, from which comes 

 all our iron, is a good example. The object in view is the 

 separation of the metal, iron, from its ores. The ores con- 

 sist of iron in combination with oxygen and, sometimes, 



