Don't try to do all parts of an experiment at the same time. Understand one part, then proceed.
Don't fail to ask yourself questions, and form an opinion about the results of an experiment before you read what the author has to say about it.
Don't fail to keep a note-book. Keep all the data and arithmetical work for future reference.
Don't leave the apparatus around after you have finished the day's work.
_=1. Introduction.=_ We should know something about iron and steel at the start, because we are to use them in nearly every experiment. The success with some of the experiments will depend largely upon the quality of the iron and steel used.
When we buy a piece of iron from the blacksmith, we get more than iron for our money. Hidden in this iron are other substances (carbon, phosphorus, silicon, etc.), which are called "impurities" by the chemist. If all the impurities were taken out of the iron, however, we should have nothing but a powder left; this the chemist would call "chemically pure iron," but it would be of no value whatever to the blacksmith or mechanic. The impurities in iron and steel are just what are needed to hold the particles of iron together, and to make them valuable. By regulating the amount of carbon, phosphorus, etc., manufacturers can make different grades and qualities of iron or steel.
When carbon is united with the _pure_ iron, we get what is commonly called iron.
_=2. Kinds of Iron and Steel.=_ _Cast iron_ is the most impure form of iron. Stoves, large kettles, flatirons, etc., are made of cast iron. _Wrought iron_ is the purest form of commercial iron. It usually comes in bars or rods. Blacksmiths hammer these into shapes to use on wagons, machinery, etc. _Steel_ contains more carbon than wrought iron, and less than cast iron.
_Soft steel_ is very much like wrought iron in appearance, and it is used like wrought iron.
_Hard steel_ has more carbon in it than soft steel. Tools, needles, etc., are made of this.
_Apparatus._ A steel sewing-needle (No. 1).[A]
[Footnote A: _=NOTE. Each piece of apparatus used in the following experiments has a number. See "Apparatus list" at the back of this book for details. The numbers given under "Apparatus," in each experiment, refer to this list.=_]