418 PHILOSOPHICAL TRANSACTIONS. [aNNO 1788. 



experiment being performed in a room with a fire. Another time I cooled some 

 distilled water, covered with oil, below 21°, by similar precautions. 



This however is by no means the greatest cooling of which water is susceptible. 

 In Fahrenheit's experiment, with an exhausted globe half full of boiled rain 

 water, it seems to have been cooled to 15°*. M de Luc also informs us, -f that 

 having filled a thermometer with some water he had purged of air by the means 

 described in his great work on the atmosphere, he exposed it to a cold which 

 sunk a mercurial thermometer to 14° of Fahrenheit's scale. The water in the 

 thermometer continued transparent, and on breaking the ball that was found to 

 be liquid, but froze that instant. In some of my experiments too with mixtures 

 of nitrous acid and water, the liquor bore to be cooled as much as 13° below 

 its new freezing point; and it has been already observed, that the addition of an 

 acid always expelled much air from the water. It is not improbable therefore, 

 that if water could be thoroughly purged of air, it would readily bear to be 

 cooled 18°, or more, below its freezing point, without congelation; though the 

 deprivation of air, obtained by boiling it, is such only as will barely enable it to 

 admit a cooling of 12°. 



Other fluids may bear to be cooled much more below their proper point of 

 consolidation. This is evidently the case in what Mr. Cavendish calls :[; the spi- 

 rituous congelation of acids. Mr. M'Nab's nitrous acid bore to be cooled from 

 30 to near 40° below its freezing point §; and Mr. Kier's vitriolic acid at the 

 strength of easiest freezing continued fluid at 29°, though its heat became 46% 

 when it began to congeal I). How low quicksilver may be cooled has not yet 

 been ascertained, but probably many degrees below — 40°. So many of the 

 above-mentioned facts were observed in the year 1783, that I then ventured to 

 remark, that " independently of these circumstances, neither stirring, agitation, 

 a current of fresh air on the surface, nor the contact of any extraneous body 

 not colder, would [necessarily] cause the water to shoot into ice, notwithstand- 

 ing the repeated assertions of authors to the contrary f." Similar experiments, 

 made in the course of the succeeding winters, have confirmed in general the 

 former results, and furnished the materials of the preceding sheets. I am very 

 sensible, that the subject still remains involved in great obscurity ; nor should I 

 have troubled the Society with an account of experiments which leave so much 

 uncertainty, had I not thought that they tended to elucidate a few points, and to 

 correct some erroneous opinions. I hope that persons inhabiting a climate more 

 advantageous for the purpose, will be induced to undertake such experiments in 

 another, and probably a more successful way, by exposure to natural cold. 



* Philos. Trans, vol, 32, p. 81. + Idees sur la Meteorologle, torn. 2, p. 105. 



+ FhUos. Trans, v. 76, p. 261. § Ibid. p. 252. || Ibid. v. 77, p. 279- 5 Ibid. v. 73, p. 358. 



