232 report— 1859. 



loped. With these features in view, the engineers constructed the engines now 

 under discussion, and to this cause may be attributed a considerable portion of their 

 success, and to the non-observance of these features the almost total failure of eco- 

 nomy in the expansive working of most steam-engines on board of steam-ships, 

 namely, by constructing large engines, going slow, without steam jackets, or super- 

 heating of steam : such engines would, of course, present a most favourable oppor- 

 tunity for improvement by adding any mode of superheating apparatus. 



From the foregoing it is also conclusive, that with the ordinary construction of 

 steam-engines afloat, small engines going fast would consume less coal per indicated 

 horse-power than large engines going slow ; but with engines such as those of the 

 ' Callao,' * Bogota,' and ' Lima ' the converse will be the case, carried, of course, 

 within moderate limits. 



In reversing the engines, the eccentrics are made to overrun the engines by a don- 

 key-engine till they arrive at the backing position, a plan which is less likely to 

 cause accident than the ordinary methods. This donkey-engine has been found to 

 be most satisfactory in its application. 



The boilers are tubular, two in number, with iron tubes. 



Each boiler has three furnaces, 3 feet 4 inches wide, and 6A feet long, or making 

 an aggregate of 130 square feet of fire-grate. 



The tubes are of iron, 288 in number, 4 inches inside diameter, and 6j feet long. 

 Each vessel has an oval steam-chest, 12 feet high and 8 feet long, and 5 feet broad, 

 with three uptakes through this steam-chest, each 2 feet diameter and 15 feet long. 

 This makes a strong form of takeup where it joins the tube plate, especially in boilers 

 firing across the ship; the feed-pipe of the boilers enters into a long flat tank or 

 shield in front of the furnaces in which the furnace-doors are formed. This shield 

 forms a protection to the firemen from heat, and makes the heat, otherwise lost, 

 available for the feed water. In the ' Callao ' there is a third coil of feed-pipe in the 

 funnel, to heat the feed water. Such then are the leading features of this machinery, 

 and the results are as follows : — 



This plan of the boilers gave steam to the engines superheated to about 400 degrees 

 by the uptakes, showing that the various systems of superheating are unnecessarily 

 complicated ; indeed, in the ' Lima,' the steam got so far above 400 degrees, that in the 

 ' Bogota ' the steam-chests were made 2 feet lower, and two small feed-pipes were 

 made to feed the boiler when too much superheated by a tap in the steam-chest. 

 The superheated steam, though upwards of 400 degrees of heat, was found quite 

 inadequate to prevent condensation in the cylinder, without the steam-jacket cock 

 being fully open. 



The writer begs to draw attention to the fact, as in the case of double-cylinder 

 engines it is so prominently observed, by comparing the respective diagrams of the 

 low- and high-pressed cylinders, especially as in those engines the cylinders are so 

 close that the diagram of one is an exact counterpart of the other, when there is no 

 condensation ; and it is somewhat curious to observe, while taking diagrams of the 

 low-pressed cylinder, the gradual development of the diagram, with the jacket-cock 

 fully open, compared with that when it is shut. 



When the steam was at a pressure of 21 lbs. above the atmosphere, the tempera- 

 ture at the surface of the water was 264 degrees, and at the top of the steam-chest 

 400 degrees Fahr., showing that the steam was surcharged to the extent of 136 de- 

 grees, notwithstanding that the steam was in direct and unimpeded contact with the 

 surface of the water. The engines made during the trial trips, which were generally 

 half a day in length, from about 23 to 26 revolutions, and indicated from 1000 to 

 1300 horse-power during that time, and consumed from 20 to 25 cwt. per hour, 

 with the surface-blow-off cocks open. The ' Callao,' ' Lima,' and ' Bogota ' have all 

 shown a consumption of from 2 to 2-J lbs. per indicated horse-power per hour best 

 Welsh coals, and the speed of the ships from 12| to 13 knots per hour. 



The steam-ship ' Callao ' has now been plying between Valparaiso and Panama 

 with Her Majesty's mails, for upwards of nine months, and has performed her work 

 in a most satisfactory manner. The distance between these ports is upwards of 

 3200 miles, and this she performs regularly on about 300 tons of coals. The 

 ' Callao ' made the run from Liverpool to Valparaiso in, I think, about 36 days, 

 steaming time, which averages about 240 miles per day during a run of 9000 miles, 



