Under the authority of an Act of the American Congress, approved Sept. 11. 1841, an extensive series of experiments was conducted by Prof. Johnson upon the evaporative power of several kinds of Coal. The number of samples tried was 41, including 9 anthracites from Pennsylvania; 12 free-burning or semi-bituminous coals; II bituminous from Virginia; 6foreign bituminous coals, viz. 1 from Sydney, Nova Scotia, sent by the Cunard Coal Mining Company: 1 of Pictou Coal, sent by the same; I of Scotch; 1 of Newcastle; 1 of Liverpool; and 1 of Pictou. From one to six trials were made on each sample, the average Quantity used per trial being 978 lbs. The experiments occupied 144 days, during each of which continuous observations were made during 12 or 14 hours.

The coals were burnt under a steam boiler, fitted with apparatus for complete regulation, the supply of water and coals being determined both by weight and measure.

The standard adopted to measure the heating power of each kind of coal was the weight of water which a given weight of each evaporated from the temperature of 212° Fahr.

The following Table gives the results of five comparisons in each of which that coal which ranks the highest is stated as 1000, and the others in decimal parts of the integer.

The same report states some results of coke-burning, from which it appears that by burning in uncovered heaps, and only cowering up the ignited mass when flame ceases to be emitted (as in many of the iron works of Great Britain, France, &c), the loss in weight at Plymouth has been found to be 17 per cent.; at Penn-y-darran, 20 per cent.; and at Dowlais (where it may be presumed the abundance of coal admits of an uneconomical management), 34 per cent. By coking in stacks, or well covered heaps of coal from 10 to 15 ft. diameter, as followed in Staffordshire, highly bituminous coals lose from 50 to 55 pr. ct. weight, and those of a drier nature from 35 to 4.0.

By coking in close ovens, a coal which, in an uncovered heap, yields only 45 to 59 per cent., yields 69 per cent. In the close oven the gain in bulk is from 22 to 23 per cent.; and while highly bituminous coals yield only 40 to 45 percent, in open heaps, and actually lose in bulk, they yield in close ovens from 65 to 66 per cent., and gain in bulk. By coking in gas retorts, the Deane Coal of Cumberland gains nearly 30 per cent, in bulk, and loses in weight 25 per cent. Carlisle coal nearly the same. Cannel and Cardiff coals gain 30 per cent, in bulk, and lose 36.5 in weight. Bewick's Wallsend loses 30, and Russell's Wallsend, 30.7 per cent, by the same process.