This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
It is sometimes necessary to cut a heavy glass bottle or cylinder. Four methods are in use. A carborundum disk having a thin edge, if kept wet and rotated at a high speed, will cut heavy glass, but the cylinder must b e fed against the wheel very gently. A better way is to make a file mark - clean. but not very deep - around the cylinder and heat it with a long slender flame while slowly rotating the cylinder all the time.It is very important that the gas flame should not spread over the surface of the glass, for it is only the file mark that should be heated. A mere glancing touch is sufficient. Usually the glass will crack off in a very clean cut.
Sometimes a fine platinum wire is wound around in the file mark and heated by an electric current I ess common is the trick of wrapping a strand of yarn soaked in turpentine around the mark and burning it The principle is the same in each case The unequal heating of the glass causes it to break. - Contributed by Harry H Holmes, Richmond, Ind. "