290 REPORTS ON THE STATE OF SCIENCE, ETC. 



Hollingworth. Also the following new members have been co-opted during the 

 year, Messrs. J. E. Hackford, H. Stafford Rayner, L. L. Robinson, and W. C. P. 

 Tapper. 



The Committee recommends that it be reappointed to continue its investiga- 

 tions, with a grant of 5?. 



APPENDIX. 



Memora7uhim on Determining the Efjicicncy of Cooking Ajjpliances. 



The efficiency of appliances for the utilisation or transformation of heat 

 energy cannot be regarded as so definite a function as in the case of mechanical 

 or electrical ones. Since no non-conductor of heat is known, the actual thermal 

 efficiency, however determined, must be varialile according to the conditions. 



In the case of cooking ranges and appliances, the conditions are so variable 

 and complicated that it is difficult to devise test methods which shall invariably 

 produce approximately the same numerical result from the same appliance on 

 two or more separate occasions. Unless this is done, any figures must neces- 

 sarily be uncertain, and no reliable comparison can be made between two 

 different appliances in respect of efficiency. 



In order that such figures should bear close relation to the efficiency of the 

 appliance as used in practice, it is desirable that the experiments should be 

 made under conditions similar to those in which the appliance is actually used, 

 but unfortunately this is, in the nature of things, impossible. No reliable figures 

 could be obtained while the apparatus was in use in cooking an actual article 

 of food, because the amount of heat transmitted to such material cannot be 

 measured, and also because of the extreme variations which arise in all the 

 observable physical magnitudes during such an operation. Thus it is impossible 

 to say when two similar joints are cooked to the same degree. It is, therefore, 

 essential that the object heated for test purposes should be very different from 

 an article of food, and such that the heat communicated to it should be capable 

 of exact measurement. 



Another difficulty in testing cooking i-anges and the like is the question of 

 ' residual heat.' The heat capacity of any cooking range is considerable; when 

 put into operation the structure at first absorbs a large proportion of the 

 heat generated, which remains after the useful operations are discontinued, and 

 is only gradually dissipated thereafter. In making calculations from the results [ 

 of a given test, this ' residual heat ' cannot be ignored unless the cookingj 

 operations have been continuous and uniformly conducted throughout, but inj 

 ordinary practice the apparatus is rarely used in such a continuous mannerJ 

 And as such ' residual heat ' is usually much larger in amount than the totalj 

 quantity utilised, it is evident that the efficiency cannot fail to be low in any 

 practical case, and will vary greatly according to the weight of the appliance 

 and the length and extent of the cooking operations. 



The determination of any true efficiency can only be made by raising the 

 apparatus to. ard maintaining it in, a 'steady state ' as nearly as possibles 

 during which period valid observations on running efficiency can be made. It. 

 is. therefore, necessary to maintain the temperature as constant as possible 

 over a long period in the steady state, and to integrate the entire results over 

 period of manv hours. 



The numerical results obtained during my experiments have in all cases beeii 

 verified by the subseouent use of the same appliance in cooking a standarc_ 

 Aveighed menu, and there has been found to be a reasonably close correspondence 

 between the fuel consumed during the practical operations and the figures 

 experimentally determined. 



The four principal sources of heat usable in cooking ranges are solid fuel, 

 gas, electrical energy, and oil fuel. Fairly complete investigations have been 

 made of solid fuel and gas, but the electrical series are in progress at the time 

 of writing, and cannot be snoken of with the same degree of confidence as m 

 the other two cases. The oil methods have not been investigated at all. 



Of these four, solid fuel is by far the most difficult to handle in an experi- 

 mental sense. It is impossible to measure the instantaneous rate of combustion. 

 This cannot by any means hitherto discovered be maintained as constant as is 



