[ 183 ] 



riments will be concordant with the 

 remit of his own. 



When I had an air worfe than 

 common air to put to the teft, I 

 found Dr. Prieftley's method ex- 

 tremely convenient, by adding one 

 meafure of nitrous air to one of the 

 air under examination ; but I al- 

 ways took care to make the two airs 

 together at the moment of their 

 mutual contact, on purpofe to a- 

 bridge the experiment. 



The principal thing to be attend- 

 ed to in putting air to the nitrous 

 teft, either by the original method 

 of the Rev. Dr; Prieitley, or by any 

 other, is to perform with the great- 

 eft nicety every circumftance con- 

 ftantly in the fame manner in the 

 various experiments ; for, if you 

 allow the two airs to itand longer 

 one time than another, if you be- 

 N 4 gin 



