VOL. LXXV.] PHILOSOPHICAL TRAXS ACTIONS. 13 



XXI. Experiments on the Loss of IVeighl in Bodies on being Melted or Heated. 

 By George Fordyce, M.D. F.R.S. p. 36l. 



Though I have made many experiments on the subject of the loss of weight in 

 bodies on being melted, or heated, I do not think, it worth while to lay them all 

 before the Society, as there has not appeared any circumstance of contradiction 

 in them. I shall content myself with relating the following one, which appears 

 conclusive in determining the loss of weight in ice when thawed into water, and 

 subject to the least fallacy of any I have hitherto made, in showing the loss of 

 weight in ice on being heated. The beam I made use of was so adjusted as that, 

 with a weight between 4 and 5 ounces in each scale, -rrW P^^^ of a grain made a 

 difference of 1 division on the index. It was placed in a room the heat of which 

 was 37 degrees of Fahrenheit's thermometer, between 1 and 2 in the afternoon, 

 and left till the whole apparatus and the brass weights acquired the same tem- 

 perature. 



A glass globe, of 3 inches diameter nearly, with an indentation at the J\ 

 bottom, and a tube at the top, weighing about 451 grains, had about /^ ^ 

 1700 grains of New River water poured into it, and was hermetically \„^^ 

 sealed, so that the whole, when perfectly clean, weighed 2150^ of a grain 

 exactly ; the heat being brought to 32 degrees, by placing it in a cooling mixture 

 of salt and ice till it just began to freeze, and shaking the whole together. After 

 it was weighed it was again put into the freezing mixture, and let stand for about 

 20 minutes ; it was then taken out of the mixture ; part of the water was found 

 to be frozen ; and it was carefully wiped, first with a dry linen cloth, and after- 

 wards with dry washed leather ; and on putting it into the scale it was found to 

 have gained about the -^ part of a grain. This was repeated 5 times : at each 

 time more of the water was frozen, and more weight gained. In the mean time 

 the heat of the room and apparatus had sunk to the freezing point. 



When the whole was frozen, it was carefully wiped and weighed, and found to 

 have gained ^ of a grain and 4 divisions of the index. Standing in the scale for 

 about a minute, I found it began to lose weight, on which I immediately took it 

 out, and placed it at a distance from the beam. I also immediately plunged a 

 thermometer in the freezing mixture, and found the temperature ]0 degrees; and 

 on putting the ball of the thermometer in the hollow at the bottom of the glass 

 vessel, it showed 1 2 degrees. I left the whole for half an hour, and found the 

 thermometer, applied to the hollow of the glass, at 32°. Every thing now beir-g 

 at the same temperature, I weighed the glass containing the ice, after wiping it 

 carefully, and found it had lost -i- and 5 divisions; so that it weighed -J^, all but 

 1 division, more than when the water was fluid. I now melted the ice, except- 

 ing a very small quantity, and left the glass vessel exposed to the air in the tern- 



