146 VOCABULARY OF 



one oscillation in a second, should be 39^- inches in length, reckon- 

 ing from the point of suspension. 



Petrifaction, an incrustation formed on any body by the deposition of 

 earthy matter from water. 



Petroleum, a liquid bitumen found on the waters of springs in various 

 parts of the world. 



Pewter, an artificial metal, being a mixture of tin, lead, and brass. 



Phosphorus, a simple combustible. See page 21. A phosphuret is a 

 combination of phosphorus with some other substance. Phos- 

 phates and phosphites are salts formed by the combination of a 

 base with phosphoric and phosphorous acid. 



Phosphuretted hydrogen gas. See page 77. 



Photometer, an instrument for measuring the intensity of light. 



Physics, the science of matter and bodies, with their motions, opera- 

 tions, &c. 



Plano-convex, a term applied to a lens which has one side flat and the 

 .other convex. 



Plano-concave, a term applied to a lens which has one side flat and the 

 other concave. 



Platinum, a metal noted for its weight, (being the heaviest of all 

 metals,) ductility, and want of affinity for oxygen. 



Plumbago, a carburet of iron ; black lead. 



Pluviometer, an instrument for measuring the quantity of rain that 

 falls. 



Pneumatics, the science which treats of the properties of the air. See 

 page 35. 



Pneumatic trough, a vessel for collecting gases. 



Potash, the vegetable alkali. See page 23. 



Potassium, the metallic base of potash. See page 22. 



Precipitation, a process in chemistry by which any body separated 

 from others in a solution falls to the bottom of the vessel. 



Prism, a glass wedge used to refract light and exhibit its different 

 colours. 



Prussia Acid, a peculiar acid of a most poisonous nature, it is pre- 

 pared from blood and animal substances. Prussian blue is iron 

 combined with this acid. 



Pump, a well-known instrument for raising water. See page 48. 



Pyrites, a combination of sulphur with a metal. 



Pyrometer, an instrument for measuring the higher degrees of heat. 



Pyrophorus. a substance which ignites when exposed to the air. 



Rainbow, a well known beautiful appearance in the heavens, caused by 

 the refraction and reflection of the rays of light. 



Retina, that enlargement of the optic nerve on which any body we 

 see is painted. See page 29- 



Retort, a chemical vessel for distillation, &c. 



Rhodium, a recently discovered metal of a white colour, remarkable for 

 its hardness and brittleness. , 



Ruby, a precious stone of a fiery red colour. The largest ruby known 

 adorns the imperial crown of Russia. 



Rust , the oxide of a metal. Gold is of all metals the least inclined to 

 rust. Platinum and silver have also but very little affinity for 

 oxygen. 





