208 



REPORT 1860. 



Rk. 6. 



the amount of heat taken out of the gases per square foot of heating surface is very 

 small ; and that the natural conclusion is that the gases pass along in straight lines, 

 and only the thin stratum in contact with the surface is cooled down. In the results 

 of the spiral boiler (fig. 6) three times the quantity of heating surface was found to 

 reduce six times the quantity of gas from the same temperature of 3200°, to a tem- 

 perature of 4800 instead of 800°, showing that a more complete turning over of the 

 gases is much wanted in our land boilers. The water evaporated per hour in the 

 land boiler referred to was found by meter to be 2000 lbs., and the coal, best 

 Glasgow quality, found to be 300 lbs. per hour ; making about 6i lbs. of water per 

 pound of coal. During the measuring of the water evaporated by the meter, indicator 

 diagrams of the engine were taken with a view to cal- 

 culate the weights of steam by the ordinary method, and 

 the calculations were found to agree with the meter ; 

 these calculations can be repeated and substantiated at 

 any time. The second type of boiler tested was that of 

 the ordinary steam-boat horizontal tubular boiler (fig. 

 4) ; the example chosen was one in a first-class ocean 

 steamer; the temperature of the furnace was found to 

 be 3200°, and the inside of the funnel about 1100°. The 

 heating surface of this boiler was 22 feet per nominal 

 horse-power, and the water evaporated about 8i lbs. per 

 pound of coal, according to the calculation from the 

 diagrams. The coal consumed was about 20 lbs. per 

 square foot of fire-grate, of the best Glasgow coal. 



The next example taken was that of a first-class ver- 

 tical tubular boiler (fig. 5), on Mr. David Napier's 

 principle, now universally selected on the Clyde for river 

 steamers. This boiler had a surface of about 22 feet 

 per nominal horse-power; the temperature of the fire 

 was found to be about 3300°, and in the funnel 1 160° ; 

 the weight of water evaporated was found by calculation to be 8| lbs. per pound of 

 coal consumed, and the weight of combustion about twenty pounds square foot of 

 fire-grate. In the spiral boiler (fig. G) of the ' San Carlos,' ' Guayaquil,' and ' Prinz 

 van Orange' the boilers were found to give the following peculiar results: — first, 

 that even with Scotch coal there was no smoke emitted from the chimney, and no 

 carelessness on the part of the fireman seemed to occasion the formation of smoke ; 

 second, that the boilers showed a bright furnace, indicating first-class draught; the 

 temperature of the funnel was found to be 480°, whilst the fire was at its greatest 

 energy. The heating surface was, in the case of the ' San Carlos ' and ' Guayaquil,' 

 2200 square feet, the coal consumed 1400 lbs. per hour, and the water evaporated 

 11 lbs. per pound of coal consumed; the fire-grate contained about 76 square feet, 

 and the rate of combustion about twenty pounds per square foot of fire-grate. The 

 heating surface of the boiler was 18 feet per. nominal horse-power; the coal consumed 

 was Glasgow best steam coal. The stoke-hole was found to be remarkably cool, 

 and the boiler, which was loaded to 52 lbs. on the square inch steam pressure, and 

 tested to 150 lbs. on the square inch water pressure, was found to be perfectly tight. 

 In the case of the ' San Carlos,' I may mention that that ship has now steamed about 

 20,000 miles, and the vessel has not been in any one port more than three days ; 

 duiing that time she has been consuming soft Chili coal for a considerable part of 

 her voyage, and the merits of the long flue show a decided advantage in this boiler 

 over the ordinary tubular boiler for the native bituminous coal of South America. 



In order to give a more extended form of the comparative evaporative power of 

 various flues and tubular boilers, the writer begs to lay before this Association the 

 accompanying Table. It shows several proportions of heating surface and evapora- 

 tive powers of several ships that have come under his notice. He can certify the 

 accuracy of most of these particulars, except that shown in the last column, w T hich 

 is taken from Professor Rankine's report on the performance of the 'Thetis.' This 

 vessel has about six times more heating surface in her boilers in proportion to the 

 coal consumed, than any example the writer is aware of. The boiler is Craddock's 

 patent boiler, though that inventor's name appears rarely to be mentioned in con- 



