376 Dr. Woods on the Amottnt of Heat produced by the 



where the metal cannot decompose water, some other fluid must 

 be substituted, as nitric acid ; and the amount of heat absorbed 

 by its decomposition allowed for in the final result. 



I would remark as a preface to the following experiments, 

 that although they arc given as if an equivalent (oxygen being- 

 one) of each metal were dissolved in a quantity of fluid equal in 

 value of being heated to 60 grains of water, no fixed weight of 

 each was used ; but according to circumstances, a portion, being 

 weighed accurately, was dissolved, and the amount of heat being 

 marked, the result was calculated. For instance, when expo'i- 

 menting with potassium or sodium, I always weighed whatever 

 happened to come from the bottle, the pieces varying from half 

 a grain to 2-^ grains. Zinc I used in lai'gcr pieces than mei'cury, 

 because it was more quickly acted on, &c., but calculated what 

 an equivalent of each would produce from knowing what the 

 weight used developed in each case. The fluid, however, was in 

 every instance the same in quantity : it amounted to 180 grains 

 when nitric acid was used, and 207 when dilute sulphuric acid 

 or water ; that is, the menstruum, the vessel containing it, and 

 the thermometer were, all taken together, equal in value of being 

 heated to this quantity of water. 



As an example of the exact steps followed, I will copy from 

 my note-book one experiment with potassium. Haraig ascer- 

 tained by previous experiments that the value of the glass tube 

 which contained the fluid and the thermometer were equal in 

 value to 27 grains, I placed in the tube 180 grains of water; its 

 temperature 59° F., temperature of room 63° F. I rolled 1| 

 grain of potassium in 10 grains of platina foil in order to make 

 it sink in the water, and having placed it in the fluid, the water 

 was decomposed, and the oxygen uniting with the potassium, the 

 temperature rose to 70° F., that is, 11°. Calculating from this 

 experiment, 1 grain of potassium would raise the temperature of 

 60 grains of water 25°'3 F., or .5 grains of potassium (equivalent 

 to 1 grain of oxygen) would raise the temperature of 60 grains 

 of water 126°'5 F. But to this must be added the heat absorbed 

 by the decomposition of the water. According to Andi'cws, 1 

 grain of oxygen uniting with hydrogen would raise the tempera- 

 ture of 60 grains of water 126°"5 F. ; therefore potassium must 

 produce by the combination of an equivalent of oxygen exactly 

 twice as much heat as hydrogen, or 253°'0 F. According, how- 

 ever, to Grassi, the combination of 1 grain of oxygen with hy- 

 drogen would raise the temperature of 60 grains of water 130° F. 



Each of the following results is calculated from a mean of 

 several experiments. 



