320 Dr. W. T. David on Heat-loss by Conduction 



linoleum were determined by subsidiary experiments. The 

 values found were 



&=Q'OO032 



and 6' = 06, 



and hence \/ — =0'008. 



V 7T 



Grids made from polished silver and polished copper sheets 

 of various thicknesses (and therefore of different thermal 

 capacities) were experimented with. The thinnest grid used 

 had a thermal capacity equivalent to - 0025 grin, of water 

 per sq. cm. and the thickest a thermal capacity equivalent to 

 0'0118 grm. of water. The results were very similar, 

 although the proportions of the heat in the grids and in the 

 backing at any instant were widely different. In view of 

 this it is believed that the various constants determined by 

 subsidiary experiments for the grid and the linoleum are of 

 a good degree of accuracy. 



Results of Experiments. 



It was found that the heat-loss by conduction was not 

 uniformly distributed over the interior surface of the vessel. 

 Thus a grid of about 5 cm. diameter placed high up on one 

 of the end covers (position A l5 fig. 1) gave results about 

 10 per cent, lower than those obtained with a grid of about 

 12 cm. diameter covering the top half of the end cover 

 (position A, fig. 1). The explanation of this would appear 

 to be that the smaller grid, on account of its position, was 

 well out of the path of the main convection currents, whereas 

 the lower part of the large grid was probably disturbed by 

 these currents and consequently received more heat from the 

 hot gaseous mixture than the small grid. 



In the experiments about to be described the large grid 

 was used, and it is thought that the measurements made with 

 this grid may without serious error be taken as giving the 

 mean value of the conduction-loss over the entire surface of 

 the vessel. 



The curves in fig. 2 relate to a 12*4 per cent, mixture of 

 coal-gas and air. Curve T shows the mean gas temperature 

 (as deduced from the pressure record) at various times after 

 ignition. Curve Gr was taken from the record traced by the 

 galvanometer and shows the heat in the grid per sq. cm. of 

 its surface. Curve H shows the total heat which has passed 



