422 KEPOKT — 1897. 



The observations taken at different pressures do not indicate any- 

 marked difference in the rate of condensation per degree-second. These 

 results, so far as they go, are in agreement with the authors' previous 

 work, but they hope to be able to obtain more conclusive evidence. 



Part II. — An Electrical Method of Measuring the Temperature of a Metal 

 Surface on which Steam is Condensing. By H. L. Callendab, M.A., 

 F.Ii.S., Professor of Physics, McGill University, Montreal. 



The object of the following experiments, which were made at the 

 McDonald Physics Building with a different apparatus, was the measure- 

 ment of the temperature of the metal surface itself by a more direct and 

 accurate method. It was also desired to verify as exactly as possible 

 whether the rate of condensation of steam at atmospheric pressure were 

 the same as at the higher temperatures and pressures at which most of the 

 preceding experiments were made. 



The condenser used for these experiments was a very thin platinum 

 tube, a quarter of an inch in diameter and sixteen inches long. The 

 thickness of the tube was only six-thousandths of an inch, and the greatest 

 difference of temperature between its inner and outer surfaces at the 

 maximum rate of condensation observed in the experiments could not have 

 been greater than a quarter of a degree Centigrade. 



The mean temperature of the metal itself was determined in each case 

 by measuring the electrical resistance of that portion of the tube on which 

 the steam was condensing. The author has had considerable experience 

 in the application of this method, which, moreover, is very easily applied 

 if suitable apparatus is available. 



The platinum tube was enclosed in an outer tube of brass or glass, and 

 steam was admitted to the space between the two tubes. A steady current 

 of condensing water was maintained through the platinum tube. The 

 amount of condensation could be inferred by measuring the flow of water, 

 and observing the difference of temperature between the inflow and the 

 outflow. In many cases the condensed water was also measured. 

 Applying a small correction for radiation, the two methods always agreed 

 within one-half of one per cent. The pressure of the steam in the outer 

 tube, which was never far from the atmospheric, was observed by means 

 of a mercury column. 



The conditions of the experiment as to flow of water and steam, size 

 and length of the external tube, &c., could be varied within certain limits. 

 The following is a summary of some of the more interesting results ob- 

 served. 



1. With a short length of condenser and a very free escape of steam, 

 the condensation observed was equivalent to 22-2 thermal units F. per 

 square foot per second, for a difference of temperature of 28°-5 F. 

 between the steam and the metal surface. This is equivalent to a rate of 

 condensation of 0'78 T.U.F. per degree-second, reckoned per square foot 

 of the surface of the metal. This was the smallest value of the rate 

 observed. The platinum tube was vertical, and the current of steam 

 downwards, conditions which tended to keep the surface of the metal 

 comparatively clear of condensed water. 



2. "With the same conditions, but with a length of tube nearly twice 

 as great exposed to the steam, the condensation observed was 22-3 T.U.F. 

 per square foot per second, for a difference of temperature of 25°-3 F. 



