TRANSACTIONS OF THE SECTIONS. 21 



of their heat, which they would otherwise afford. Hence, those chemists 

 who, with M. Berthier and Mr. Richardson, estimate the calorific powers 

 of coals by the quantity of carbon which they contain, or the quantity 

 of oxygen which they consume, have arrived at very erroneous conclu- 

 sions. The amount of error may be detected by experiments on the 

 cokes of flaming coals. M. Berthier examines coals for their propor- 

 tion of carbon, by igniting a mixture of each, finely pulverized, with 

 litharge, in a crucible, and estimates 1 part of carbon for every 34 parts 

 of lead which is reduced. I have made many researches in this way 

 with both charcoal and anthracite, and have obtained very discordant 

 results. In one experiment, 10, grains of pulverized anthracite, from the 

 vale of Swansea, mixed with 500 grains of pure litharge, aff'orded 380 

 grains of metallic lead; in a second similar experiment, 10 grains of the 

 very same anthracite afforded 450 grains of lead ; in a third, 350 grains. 

 In one experiment with good ordinary charcoal, fresh calcined, 10 

 grains, mixed with 1,000 of litharge, afforded no less than 603 grains 

 of metal. The crucible was in each case covered and luted. My 

 future researches, which are intended to embrace every important va- 

 riety of fuel, natural and artificial, will be made with an apparatus 

 somewhat modified from that here described. Three furnaces will be 

 inclosed within each other, with a stratum of air or ground charcoal 

 between each, so as to prevent all loss of heat into the atmosphere, and 

 thereby to transfer the whole heat disengaged by combustion into a 

 large body of water, of a temperature so much below that of the at- 

 mosphere at the beginning of the experiment, as it shall be above it at 

 the conclusion. 



On a method of JiUing a Barometer without the aid of an Air-pump, 

 and of obtaining an invariable level of the surface of the Mercury in 

 the Cistern. By Prof. Stevelly. 



Prof. Stevelly said that it was very difficult to fill a barometer tube 

 so as to be quite free from air and moisture. Mr. Daniell, in his Me- 

 teorological Essays, proposed to fill the barometer under the exhausted 

 receiver of the air-pump, and actually had the barometer of the Royal 

 Society so filled by Mr. Newman, under his own superintendence ; but, 

 although an expert London working optician might be found capable of 

 executing successfully such a task, yet few in the country could hope 

 for such an advantage ; and, in fact, although he had attempted the 

 process at Belfast, he had never succeeded. After some consideration, 

 the following simple mode of using the Torricellian vacuum of the tube 

 itself, instead of the air-pump, in filling it, occurred to him. He heated 

 the mercury as hot as it could be handled, and filled the tube, in the com- 

 mon way, to within half an inch of the top ; then worked out, in the usual 

 way, all air-bubbles, as perfectly as possible ; filled up the tube to the 

 top, and inverted it in a cup of hot mercury, when of course it sub- 

 sided, in the upper part of the tube, to the barometric height ; he then 

 placed his finger on the mouth of the tube, under the mercury in the 



