160 STATE BOARD OF AGRICULTURE. 



MY EXERCISE. 



Young men, this morning I am pleased to call your attention to the 

 boiling point of water, usually marked at 212 degrees Fahrenheit or 100 

 degrees Centigrade — under certain conditions. The conditions and vari- 

 ations are the peculiarities to be noted. Here (exhibiting) is a glass 

 flask, through the sides of which we can observe the action of the water 

 and read the temperature of a contained thermometer. Over the flame 

 one of the first things noticed is the formation of bubbles on the bottom 

 of the dish — top side of bottom. One by one the bubbles begin to let go, 

 start for the top, but collapse on the way up. If we listen we notice the 

 collapsing of the bubbles produces a peculiar sound. This sound has a 

 technical name. It is called the "tea kettle singing." A brisk fire 

 makes this singing period very short, because the bubbles begin to 

 reach the surface. At the surface no noise is produced. Bubbles rise 

 and explode at the surface. The water is now boiling. 



The temperature has been rapidly rising, but now at the instant the 

 bubbles begin to explode at or above the surface, the temperature comes 

 to a standstill. The temperature is now 210 degrees Fahrenheit on an 

 accurate thermometer, and independent of the intensity of the flame the 

 temperature will remain 210 until the water has boiled away. 



Boiling water is largely used in operations, directly and indirectly, at 

 the farm. In the State of Michigan the temperature of boiling water 

 seldom varies more than one degree more or one degree less than 210, Fah- 

 renheit. This would lead one to think that 212 degrees, as usually 

 marked, was wrong. Two hundred and twelve is right for the sea 

 level, because a temperature of 212 is necessary to force the bubbles to 

 the top at sea level. But in Michigan we are about 1,000 feet above sea 

 level; the air is lighter, pressure less, and only 210 degrees is required 

 to send the bubbles to the top. If the mouth of the flask is partly closed 

 so as to imprison part of the escaping steam, the pressure is raised and 

 at the same time the temperature of the boiling water. A handkerchief 

 placed lightly over a flask's mouth will often raise the temperature 10 

 degrees. 



The raising the temperature by raising the pressure has several impor- 

 tant applications, one of which is process canning, without sugar or other 

 preservatives. Fruit does not keep because of the presence of germs 

 with Latin names; these germs are not killed by the introduction to the 

 temperature of 210 or 212. In fact, about 300 degrees is required to deal 

 death to the germ. So the fruit, corn, tomatoes, peas, etc., are preserved 

 in water by hermetically sealing after being placed in a steam boiler, 

 where the pressure approximates 40 pounds to the square inch, which 

 corresponds to the temperature above. I have prepared a table to show 

 the relation of temperature and pressure. 



