1 84 GENERAL SCIENCE 



The chemist explains the acid effect of solutions upon litmus or 

 other test papers ("indicators") as due to the presence of free hydrogen 

 ions, while the alkaline effect is due to the presence of free hydroxyl 

 ions. 



The formula used in place of the name of any chemical compound 

 not only is a shortened way of writing its name, but it also states at a 

 glance what elements enter into the compound, their grouping, and 

 their weight proportions. All this must be known by the chemist 

 before the formula can be written. 



An equation sets forth what substances enter into a chemical change 

 as factors, and what are the products of the change. The combined 

 weights of factors and of products must be equal, as must the number 

 of atoms on the two sides of the sign of equality. 



Any use of equation writing to express what is thought to have 

 occurred, or what may occur in a chemical change, is liable to lead to 

 wrong conclusions. Its proper use is to set forth what is known to have 

 occurred. It is a means for stating facts that have been verified by 

 exacting tests. 



The valency of any atom or radical is simply a number. It tells 

 how many hydrogen atoms will replace the atom or radical, or with 

 how many hydrogen atoms it will unite. 



A radical is a group of atoms which in chemical changes behaves 

 like a single atom. 



ELECTRICITY AND CHEMICAL CHANGES 



In the study of electricity from cells there is reason to 

 believe that the electrified condition passing along a circuit 

 and constituting the current is being maintained by chemical 

 changes occurring in these cells. It is also assumed that this 

 outward passage of the electrified condition is by way of the 

 carbon plate in the dry cell, or copper plate in the simple cell. 



Where the terminals of a broken circuit are put down into 

 an electrolyte, that electrode by way of which the current 

 enters the electrolyte is called the anode (way in), while the 

 one from which the current leaves the electrolyte is known 

 as the cathode (way out). When a current sufficiently strong 

 is passedjthrough dilute sulphuric acid as the electrolyte, 



