i6e EXPERIMENTS akd OBSERVATIONS 



tioned gentleman ; viz. " The difference in the purity 

 of the air at different times, is much greater than the 

 difference between the air of the different places," In- 

 deed moft of the experiments related by Dr. Ingenhoufz 

 alfo tend to confirm it. In general the difference in the 

 air of different places at the fame time was by no means 

 conliderable. 



I Ihall now with more confidence relate the experi- 

 ments I myfelf performed : but previous to this recital 

 I fliall give a brief account of the method 1 purfued. 



It is neceflary to remark, that every experiment I fhall 

 relate is the refult of at leafl two different trials. 



Moft authors who have engaged in this fubjedt ufed 

 eudiometers of a different conftrudlion ; I adopted the 

 moil fmaple as the beft. Thofe who defire a particular 

 defcription of thefe inftruments may be fatisfied by re- 

 ferring to the Encyclopsedia and different parts of Dr. 

 Frieftley's Treatife on Air. Mine is as follows ;* 



I had a glafs tube about 14 inches in length, and in 

 diameter nearly half an inch, provided with a graduated 

 fcale, made fo as to flide upon the tube up or down as 

 occafion required. This fcale was divided into one hun- 

 dred equal parts. 



My meafure was a fmall fmelling bottle, containing 

 3j. and gr. xvj. of clear pump water. The fpace occu- 

 pied in the tube by a bulk of air which this meafured, 



* The atmofphere is proved by inconteftable experiments to confift in 

 general of, 



Oxygen gas 0.27 

 Azotic gas C.72 and 

 Carbonic acid o.oi. 

 Ttii a fad well known to chemifts, that nitious air will combine with 

 oxygen gas and form a compound, viz. the nitric acid. As thefe two gafes 

 combine they alfume a ftate approaching nearer to that of a folld and confe- 

 quently occupy lefs fpace than they did before their union. Upon this 

 diminution of bullc depends our eflimatlon of the purity of the air. The 

 greater the contraflion, the purer we fuppofe the air under tilal. 



could 



