612 PROCEEDINGS OF SECTION H. 



results of boilers of the same capacity for purposes of comparison, 

 and it obviously is unfair to compare the boiler with a larger 

 boiler. 



Sir Frederick Bramwell has estimated that the loss due to radia- 

 tion in a large boiler is often less than 3^ per cent., while in a 

 small boiler he found that this loss increased to 16|- per cent, of 

 the total amount of heat produced by the consumption of the fuel. 

 In these experiments the writer took careful readings of the tem- 

 peratures around the boiler, and estimated that the loss from this 

 source was not less than 7i- per cent. On this account, making 

 comparison with other boiler performances, it will be fair to calcu- 

 late the efficiency of this boiler by comparison with the furnace 

 efficiency. This is the usual mode of calculating boiler efficiencies. 

 The formula generally adopted to find the furnace efficiency is taken 

 from Rankine. 



Ei = EB^(l -f ^ F) 



Where Ej = furnace efficiency in lbs. of water evaporated at 

 212° equivalent to each lb. coal consumed 

 E =: evaporative value of fuel in the same measure 

 S =: ratio of total heating surface to total grate area 

 B = '92 (arithmetical constant) 

 A ^ -5 (arithmetical constant). 



In these tests the value of E, found when the boiler was tested 

 to its iitmost capacity, as in trial No. 2, works out as 7'63lbs., 

 whereas the result actually obtained without making any allowance 

 for ashes and clinker, which were drawn from the fire hot, nor 

 estimating moisture in full, works out as 6"78lbs., showing the 

 boiler as having the remarkable efficiency of 88-1 per cent. 



The locomotive boiler gives almost as high results as can be 

 obtained with any boiler of ordinary types. The trials on the 

 Victorian railways show the evaporation when using the same fuel 

 as 9-4lbs. Malung allowance for the difference in size of boiler 

 and consequent efficiency of furnace, it will be seen that the result 

 gained with the Shann boiler is much better, and then it has 

 further to be remembered that in the locomotive boiler there is 

 considerable waste of steam power due to the forced draught, which 

 loss helps the apparent evaporative result. In addition to this 

 allowance should be made for moisture in the steam ; this, in the 

 absence of calorimeter tests, may reasonably be assumed to reduce 

 the result to 8-5 lbs. evaporation. 



In making these comparisons the writer has carefully avoided 

 any assumptions which might seem too favorable to the water tube 

 boiler. In the matter of radiation his assumptions are hardly so 

 high as his observations would warrant, but he purposely avoids- 

 any circumstance which might give too favorable an impression for 

 fear too sanguine anticipations might not be fully realised when 

 this boiler came to be tested on a larger scale. Even should this 



