Equilibrium of Temperature of Bodies in Contact. 381 



agent, becomes of a fine emerald green. The following analysis was 

 made of it : — 8*2 grains, previously dried at a temperature of boiling 

 water, were submitted to a long-continued red heat in a small green 

 glass tube, to which a chloride of calcium tube was attached; it 

 lost 1*0 grain, which corresponded with the weight gained by the 

 absorption tube ; 8*2 grains dissolved in dilute nitric acid, and pre- 

 cipitated while boiling by caustic potash, gave, after the necessary 

 treatment, 4*5 grains of the red oxide of manganese ; the solution 

 was then acidified by sulphuric acid, and evaporated to dryness to 

 expel the nitric acid, redissolved, deoxidized by alcohol and the 

 oxide of chromium thrown down by ammonia, again evaporated to 

 dryness, to avoid the possibility of any of the oxide being in solu- 

 tion, and the oxide of chromium, well washed, gave 2*3 grains. We 

 have therefore 



4*5 grains red oxide manganese. . =4*188 protoxide 

 2*3 ... protoxide chromium . . = 3*000 chromic acid 

 1*0 ... water 1*000 water 



8*188 



By calculation this should be . . 4*141 protoxide 



3*014 chromic acid 

 1*043 water 



Or, 1 atom chromic acid -f 2 atoms protoxide of manganese + 2 

 atoms water. Represented by Cr 3 + 2 Mn O . + 2 H . O 



April 19. — The following communications were read : — 



" On the Equilibrium of the Temperature of Bodies in contact," 

 by E. A. Parnell, Esq. 



In reference to observations recently made by Mr. Hutchinson on 

 the difficulty of raising the temperature of any substance to the de- 

 gree of the medium by which the heat is applied*, Mr. Parnell ob- 

 serves, " From what I know of the mode in which Mr. Hutchinson 

 operated, it is probable that a loss of heat occurred by radiation from 

 the substance operated on ; by radiation, first to the cover of the 

 bath, and from this to external objects. On adopting precautions 

 to avoid this source of error, I found that in a steam-bath the tem- 

 peratures attained by substances, were 



1. Olive oil & degree below the temperature of the steam. 



2. Water § 



And in a water-bath, — 



3. Water ^ degree below the temperature of the water. 



4. Vapour of aether 1 ... ... ... 



5. Air 1 



In the two first experiments, the apparatus used was a large flask, 

 closed with a cork, having several perforations, through one of which 

 was admitted a wide tube containing the liquid operated on, the 

 tube not dipping so far as the surface of the water in the flask, which 

 was kept boiling. 



In the remaining three a copper water-bath was employed, the 



[* An abstract of Mr. Hutchinson's paper will be found at p. 318.] 



