The ideas which have been given in this and the preceding books can be applied in many ways to the problems of any subject. There is no attempt on the part of the author to work out all applications, but merely to suggest a few possible ones and leave the rest to the student. Each will think of different methods, and those aids which each one works out for himself will be most valuable and most easily recalled. The Elemental Substances The six elemental substances of the organic world are: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulphur, which can be easily remembered by the following: The Organic World--Can Have No Other Principal Story. The initials of each of the words following "World" stand for one of the elements. Chemical Formulae Remembering of chemical formulae can be simplified very greatly by reducing the formulae to an idea using the initialing plan; for example, the formula for Wood Alcohol is CH3OH. This formula in itself has no meaning, and is difficult to carry in mind. By using the initials you can easily make some ideas which will represent this formula and help you to remember it, as for example: CAT HAD ham ON HAND. In this formula the C of Cat stands for Carbon, the H of Had for Hydrogen; Ham being a Code Word for 3 is indicative of 3 atoms of Hydrogen, and the O. H. is represented by the O and H of On Hand. The formula for Glycerine is C3H5(OH)3, and can be remembered by the following idea: COME HEEL O HAM. In this example notice that the first letter of the word initials the substance and the last letter the number of atoms by the number code. As COME: C for Carbon, and M for 3. HEEL: H for Hydrogen, and L for 5. O for Oxygen. HAM: H for Hydrogen, and M for radicle 3 times. Use whichever method suits you best. The formula for Carbolic Acid, C6H5OH, or CASH HAUL O, HAY. The formula for Benzine, C6H6, or CASH HASH. Hardness of Substances It is often valuable to know the degree of hardness of different substances, and these can easily be remembered by the following list. In degree of relative hardness the list is as follows, the hardest coming first. Diamond Corundum Topaz Quartz Iridium Apatite Bell Metal Boric Acid Rock Salt Kaolin Take Kaolin as a basis. The number opposite each substance in the following list indicates its comparative degree of hardness in relation to Kaolin: 1 Kaolin TIE See tie on Kaolin 2 Rock Salt SNOW Poured over Rock Salt 3 Boric Acid HOME Built of Boric Acid 4 Bell Metal WIRE Swinging a Bell 5 Apatite WHEEL With a big appetite for running 6 Iridium SASH Irritating the wearer 7 Quartz EGG Quartz taken from an Egg 8 Topaz IVY To pass the Ivy 9 Corundum WHIP Made Cora run 10 Diamond TOES Set with Diamonds