36 On air PRODUCED by mi 



No. V. 



Experiments on the Produ3ion of Air by the Freezing of 

 Water. By Dr. Joseph Priestley. 



Read AprU TN 1 793 , whcii I was in England, I published 

 lis, 1800. J^ a couife ot experiments on the generation of 

 air from water ^ and after my arrival in this country, I 

 refumed the experiments, and publillied difequel to them. 

 The refult of the whole was that, after all air had been 

 extradled from any quantity of water, either by heating, 

 or by taking ofF the preffure of the atmofphere, when 

 ever any portion of it was converted into vapoui', a 

 bubble of permanent air was formed, and this was al- 

 ways phlogifHcated. The procefs with the Torricellian 

 vacuum 1 continued fome years, and found the produc- 

 tion of air equable to the laft. The necefl'ary inference 

 from this experiment is, either that water is convertible 

 into phlogiflicated air, or that it contains more of this 

 air intimately combined with it than can be extratled by 

 thefe proceffes in any reafonable time. 



Finding that no air is contained in ice that is free from 

 vifible bubbles, I thought to afcertain the truth of one 

 or other of thefe hypothefes by expofmg to froft a quan- 

 tity of water from which 1 had, by repeated pi-ocefTes 

 with the Torricellian vacuum, expelled all the air that I 

 poffibly could ; thinking, that "if it really contained no 

 air, it would appear by the ice being perfectly folid ; fo 

 that when it was melted no air would be got from it. 

 This experiment I repeated feveral times, but always 

 found that though the outfide of this ice was perfedlly 

 tranfparent, and free from air, the central parts were 

 opaque ; and though there were no diftinil air bubbles 

 in it, yet when it was melted a great number of bubbles 

 iflued from it. The whole quantity, however, was not 



greater 



