434 



ESTIMATION OF THE AMOUNT OF HEAT. 



cause it to give off heat by conduction or radiation, then its tem- 

 perature falls. 



A good example of this is the skin, which varies greatly in temperature accord- 

 ing to the temperature of the surrounding medium, whether it is covered or 

 uncovered, whether it is dry or moist with sweat (which abstracts heat when 

 it evaporates). When much cold food or drink is taken the stomach is cooled, 

 and when ice-cold air is breathed the respiratory passages as far as the bronchi 

 are cooled. 



211, Estimation of the Amount of Heat 



Calorimetry. 



Calorimetry is the method of determining the amount of heat 

 possessed by any body, or what amount of heat it is capable of pro- 

 ducing. The unit of measurement is the "heat-unit," i.e., the amount 

 of heat (or potential energy) required to raise the temperature of 1 

 gramme of water, 1C. (see Introduction). 



Experiment has shown that equal quantities of different substances require very 

 unequal amounts of heat to raise them to the same temperature, e.g., 1 kilo, 

 water requires nine times as much heat as 1 kilo, iron to raise it to the same 

 temperature. In the human body, therefore, which is composed of very different 

 substances, unequal amounts of heat will be required to .raise them all to the same 

 temperature. The same amount of heat transferred to two different substances 

 will raise them to different temperatures. Hence, bodies of different temperatures 

 may contain equal amounts of heat. The amount of heat required to raise a 

 definite quantity (e.g., 1 gramme) of a substance to a certain higher degree (e.g. , 

 1C.) is called "specific heat" (Wilkie, 1780). The specific heat of water (which of 

 all bodies has the highest specific heat) is taken as 1. By "heat-capacity" is 

 meant, that property of bodies in virtue of which they must absorb a given amount 

 of heat in order to have a certain temperature (Crawford). 



Calorimetry is employed: I. To determine the specific heat of the 

 different organs of the body. Only a few observations have been made. 

 The mean specific heat of the following animal parts (waters 1) is: 



Human Blood = T02 (?) 



Arterial = 1'031 (?) 



Venous = 0'892 (?) 



Cow's Milk = 0-992 



Human Muscle = 0741 



Ox = 0-787 



Compact Bone = 0'3 



Spongy ,, = 071 



Fat-tissue = 0712 



Striped Muscle = 0'825 



Defibrinated Blood = 0'927 



The specific heat of the human body, as a whole, is about that of 

 an equal volume of water. 



Kopp has estimated the specific heat of solids and fluids by the following 

 method (Fig. 169) : The solid to be investigated is broken in pieces about the size 

 of a pea, and placed in a test-tube, A, with thin walls, which is closed above with 

 a cork, from which a copper-wire with a hook on it projects. The test-tube con- 

 tarns a certain quantity of fluid which does not dissolve the substance, but which 

 lies between its pieces and covers it. It is weighed three times to ascertain the 



