How much is a bushel of coal?
Interpreting coal consumption data from texts predating "The Weights and Measures Act 1835" requires caution, as measurements were not standardized across England. Prior to this act, various local and regional systems of weights and measures coexisted, making direct comparisons and conversions challenging.
Peck and bushel, primarily volume measurements, were commonly used (with 4 pecks equaling 1 bushel). However, the actual weight these volumes represented could vary significantly depending on the region and the type of coal. To convert these to weight, we can use coal density [21] or refer to historical discussions on coal weight per bushel [30].
Before standardization, England had a patchwork of local measurement systems. The lack of standardization had profound effects on commerce and industrial development. Merchants often had to convert between different systems when trading across regions, leading to potential errors and disputes.
According to historical sources, a bushel of Newcastle coal ranged from 80 to 84 lbs., while a heaped bushel of Welsh coal could weigh up to 101 lbs. It was also noted that ¾ of a hundredweight equaled one bushel. The Weights and Measures Act 1835 established the imperial hundredweight (cwt) at 112 lbs., defining a bushel as 84 lbs. For consistency, all calculations on this website assume a coal bushel weighs 84 lbs. (38.1 kg) unless otherwise specified by historical sources.
The heating value of bituminous coal ranges from 8.06 to 8.39 kWh/kg [22]. Using an average of 8.24 kWh/kg, we can estimate that one bushel of coal provides approximately 314 kWh of heat energy.
It's important to note the inherent uncertainties in these calculations:
- The heating value range introduces a ±4% uncertainty.
- Historical references to "1 bushel per hour" may actually mean between 7/8 and 9/8 of a bushel, as most citations use quarter fractions. This introduces an additional uncertainty of ± 12.5%.
When comparing results from different sources, a total error margin of ±15% should be considered.
These factors highlight the challenges in precisely interpreting historical coal consumption data and emphasize the need for caution when drawing conclusions from such information.
The custom of measuring coals by a bushel is rarely practised, except for those coals which are transported by sea, and which are, in consequence, chargeable with a duty. The great exports of coals by sea are from Newcastle in Northumberland, and Swansea in South Wales, and Workington in Cumberland. It is usually implied that coals are brought from one or other of those places, wherin they are reckoned by bushels ; and both, the Newcastle and Swansea coals are commonly of a better quality than the inland coals of Staffordshire, Yorkshire, or Lancashire, which are reckoned by the hundred weight (= 112 lbs.) and the ton (= 2240 lbs.)
The mode of measuring coals in a bushel is subject to considerable uncertainty, because they are directed to be heaped up in a conical form, above the top edge of the bushel, but the height of the heap is only determined by the eye. It requires a reference to several acts of parliament to find what the dimensions of the legal coal bushel ought to be. By an act of parliament, 16th and 17th year of King Charles II. it is enacted, that all coals brought into the river Thames, and sold by the chaldron, shall be at the rate of 36 bushels heaped up.
According to an act of the 12th of Queen Anne, the coal bushel must be round, with an even bottom, and be 19½ inches, from outside to outside, and must contain one Winchester bushel, and one quart of water. Now, the Winchester bushel (also called the malt bushel) according to an act 13th William III. 1713, is a circular measure, 18½ inc. diam., and 8 inc. deep; this contains 2150.42 cubic inches; and a quart = 67.2 cubic inc. ; hence the contents of the coal bushel should be 2217.62 cubic inch.; and a cylindrical measure, to contain this quantity, would be 18.8 inc. diam., and 8 inches deep. Again, another act, 47th George III. (1807) directs that the coals shall be heaped up above the bushel, in the form of a cone, at least 6 inches high, and of the same size at the base, as the outside of the measure, viz. 19½ inc. diam.; this cone will contain 597.3 cubic inches.
The legal coal bushel may, therefore, be stated to contain 2815 cubic inches, or 1.63 cubic feet. Three bushels of coals are put into a sack, and 12 such sacks (=36 bushels) make a chaldron. This is the mode of reckoning coals by retail in London, but in the wholesale trade, when 5 chaldrons are measured, an ingrain, or extra allowance of 1/20 is given, making 189 bushels in 5 chaldrons, which is called the pool measure.
The weight of coals varies considerably in the different sorts, but the chaldron (=36 bushels) is usually reckoned to weigh 27 hundred weight ( x 112)=: 3024 lbs., which is at the rate of ¾ of a cwt. (or 84 lbs.) per bushel : this number has been adopted in the present work, because it is the actual weight of the best qualities of the Newcastle coals, though inferior sorts are not above 78 or 80 lbs. per bushel.
John Faray, p. 337