APPENDIX. 303 



part throughout the United States. In it, the range between 

 the freezing and boiling points of water is divided into 180 

 degrees ; and as the greatest possible degree of cold was 

 then supposed to be that produced by mixing snow and com- 



Imon salt, it was made the zero, or commencement of the 

 ^6cale, hence the freezing point became 32° and the boiling 

 ^point 212°. Reaumer's thermometer, which was formerly 

 «sed in France, divides the space between the freezing and 

 ^boiling of water into 80°, and places the zero at the freezing 

 -point. The Centigrade thermometer places the zero at the 

 freezing point, and divides the range between it and the 

 boiling point into 100°. This has long been used in Swe- 

 den under the title of Celsius's thermometer. Dc Lisle' s 

 thermometer is used in Russia. The graduation begins at 

 the boiling point, and increases towards the freezing point. 

 The boiling point is marked and the freezing point 150* 



LESSON 65. 



\mple Combustibles. The following is an enumeration and 

  classincatioa of the simple bodies in general. I. Compre- 

 "hending the imponderable agents, Heat or Caloric, Light, and 

 Electricity. II. Comprehending agents capable of uniting 

 with inflammable bodies, and in most instances of effecting 

 their combustion, — Oxygen, Chlorine, and Iodine. Many 

 learned chemists have doubted whether Chlorine and Iodine 

 were supporters of combustion, any farther than they contain 

 oxygen. They are classed among the simple bodies because 

 they have not, as yet, been resolved into other ingredients. 

 The name chlorine is simply expressive of its greenish colour, 

 and iodine of its violet colour. III. Comprehending bodies 

 capable of uniting with oxygen, and forming with it various 

 compounds, — 1. Hydrogen, forming water. 2. Bodies form- 

 ing acids. Nitrogen, forming nitric acid. Sulphur, forming 

 sulphuric acid. Phosphorus, forming phosphoric acid. Car- 

 bon, forming carbonic acid. Boron, forming boric acid. 

 Fluorine, forming fluoric acid. 3. Metallic bodies, which 

 have been divided into the seven following classes. 1st. 

 The metals which combine with oxygen and form alkalies. 

 These are potassium, sodium, and lithium. The volatile al- 

 kali ammonia has been found by Sir H. Davy to be a triple 



