TltANSACTfONS OP THE SECTIONS. 



209 



nexion with the said vessel. Efficient, however, as this boiler must be as an evapo- 

 rator, it cannot possibly accomplish the quantity shown in this Table. 



The theoretical quantity of water capable of being heated from 90°, and evaporated 

 at, say 212°, with an infinite quantity of heating surface and a perfect fire, is some- 

 where about 13^ lb3. per pound of coal; whilst from the diagrams represented in 

 Professor Rankine's report of the 'Thetis' performance, 18 lbs. weight appear to 

 be about the quantity of water per pound of coal. This calculation I have made 

 from the diagrams published, and any party interested may repeat the calculations. 



The calculation is made as follows : the area of the large cylinder, as shown in the 

 diagram, is 1380 square inches, or9'583 square feet. The four revolutions of piston 

 marked on the diagram 49i, 52, 53, and 52 revolutions per minute, with a stroke of 

 2£ feet, or say 25S'12 feet per minute, gives 25S-12X 9'583X 60=146433 cubic feet 

 per hour. And if we take the average pressure shown in the four diagrams at the 

 end of the piston stroke, supposing the barometer to be 14*5 lbs., we find the weight 

 of that steam to be about 44 cubic feet per pound: this number therefore, divided 

 by 44, gives the quantity of steam as 3300 pounds per hour ; to this must be added 

 • a V for contents of ports and clearance, which makes 3465 pounds of steam. 



This clearly gives the weight of the steam per hour given out of the cylinders 

 after the work is performed, to this therefore must be added the quantity of heat 

 that must have disappeared during the performance of the work ; this, in the case 

 of the 'Thetis,' is about \ of the entire heat; we must therefore add \, or say 

 3465 + 693 = 4153 pounds of water must have been raised from a temperature of 

 about 100° and evaporated, or say 18 lbs. of water to the pound of coal said to be 

 consumed ; this result is about equal to 20 lbs of water evaporated at 212°, to the 

 pound of coal consumed ; a quantity quite absurd. 



Comparisons of certain Results obtained fram Certified Diagrams of Steamers' Elk,' 'Earl of 

 Aberdeen,' ' Valparaiso,' 'Pride of Erin,' ' Inka,' ' Earopa,' ' Cambrian,' and ' Thetis.' 



Nominal H.P 



Indicated ditto 



Proportion of indicated 

 H.P. to nominal II.P, 



Diameter of Cylinder. . . 



Length of Stroke 



Number of Strokes pei 

 minute 



Boilers, Flue or Tubular 



Area of Fire-grate .... 

 Area of Heating Surface 

 Coals consumed per hr 



Quality of Coal , 



Steam evaporated per 



lb. of Coal 



Estimate, water evapo- 

 rated 



Coal consumption per 



indicated H.P 



Fire-grate per nominal 

 H.P 



Elk. 



250 

 780 



3-28 

 57in. 

 5 ft. 6 in. 



25 



Tubular. 



144ft. 



4000 



33601bs. 



Glasgow best 



7354 



8-1 



4-071 



■57G 



Earl of 

 Aberdeen. 



380 



780 



205 



7 0in. | 



6ft. 



17-5 



Flue. 



190ft. 



4300 



3584 



Newcastle. 



6-87 



7-4 



4-358 



•5 



Valpa- Pride of 

 raiso. Erin. 



320 

 826 



2-581 

 Two 52 

 Two 90 



5ft. 



21 



Flue. 



130ft. 



2400 



2520 



Welsh. 



7-74 



8-6 



305 



•406 



400 

 960 



2-4 



72 

 5ft. Gin. 



M 



22 



Flue. 



252 



4400 



4928 



Welsh. 



7-159 



7-9 

 5-126 

 •63 



Inka. 



80 

 272 



3-8 

 Two 2S 

 Two 48 



3ft. 



32 



Flue. 



50 



480 



672 



Welsh. 



8-1 



9-0 



2-47 



•625 



Europa 



648 

 1207 



1-863 



I 90 



8ft. 



15J 



Flue. 



314 



7000 



5100 



Welsh. 



7-7 



8-5 



4-2 



•484 



Cambrian, 



472 

 1072 



2-272 

 77-5 i 

 7ft. 6in. 



16 



Flue. 



247 



5400 

 4480 

 Welsh. 



7-509 



4-17 



•536 



Thetis 



80 



226 



2-82 

 One 21 

 One 42 

 2ft. 6in 



} 



52 



{Craddock's 

 Patent. 



About 4000 



226 



Good. 



15 lbs. about. 



laibs. 



1018 



It therefore appears that in the report referred to, the indicated power of the said 

 diagrams may be correct, but the coals said to be consumed per indicated horse- 

 power per hour, namely 1'08, must be wrong ; and before a proper comparison could 

 be established between the merits of the ' Thetis' ' boiler and that of any other boiler, 

 a correct trial of the former would be necessary. In the mean time we have but to 

 1860. 14- 



