﻿162 Mr. C. Tomlinsorr's Historical Notes on some 



Society gave the sanction of its high authority to a Report on 

 the subject prepared by some of its most distinguished mem- 

 bers, and published in the Transactions for the year 1777. In 

 this Report the want of fixity in the boiling-point of water under 

 a constant pressure is noticed, and the cause is referred to the 

 depth of water in the vessel, which causes it to boil in gusts. It 

 was found, however, that the elasticity of the steam from boiling 

 water fairly represents the atmospheric pressure, and it was re- 

 commended that the water be boiled in a metal vessel constructed 

 so as to allow the bulb, and nearly the whole of that part of the 

 stem that contained mercury, to be surrounded by the steam. 



3. I am not aware that in this Report, or in the results pre- 

 viously published that led to it, it is anywhere stated that the 

 nature of the vessel influences the boiling-point. That fact was 

 distinctly brought forward by M. Achard in 1785"^. Distilled 

 water was boiled in a brass cylindrical vessel by means of a spirit- 

 lamp, the thermometer-bulb being within half an inch of the 

 bottom. Under these conditions the temperature was constantly 

 varying, although the water appeared to boil equably. Blowing 

 on the side of the vessel, opening and shutting a door, or any- 

 thing that produced an agitation in the air caused a fall in the 

 thermometer of 1*12° R. When the water was boiled in a ma- 

 trass of white glass, there was no variation in the boiling-point 

 as indicated by the thermometer. Achard performed a large 

 number of experiments on the boiling-point of water in vessels 

 of silver, brass, porcelain, earthenware, glass, &c, many of them 

 being articles in domestic use; and he gives drawings of them in 

 three folding plates, with measurements of their dimensions, to 

 justify his conclusion (afterwards found to be erroneous) that in 

 vessels of the same material the temperature of boiling water 

 varies according to the size of the opening. There is no doubt, 

 however, as to the influence of the vessel on the boiling-point. 

 He says: — "Le degre de chaleur de Feau en ebullition dans dif- 

 ferens vases est different pour la meme pression atmospherique 

 quoique les vases soient chauffes de la meme maniere et quails se 

 trouvent dans le meme bain de- sable." His idea was, that, metal 

 being a good conductor, the heat readily escaped from it when the 

 air was agitated, while glass retained its heat, and hence the oscil- 

 lation of the mercury in the one case and its fixity in the other. 

 He concludes his memoir with the remark u that the experiments 

 prove that the degree of heat of boiling water under an equal 



* Nouveaux Memoires de V Academic Roy ale de Berlin for 1785, pub- 

 lished in 1/87- The following is the title of the memoir: — "Experiences 

 faites dans la vue de s'assurer si le degre de chaleur de l'eau pure bouillante 

 est un degre fixe et invariable, independant de toute autre circonstance que 

 de la pression de l'atmosphere." 



