200 PHILOSOPHICAL TRANSACTIONS. [aNNO 1787, 



greater, but its quality also much superior to that yielded when the sun's rays 

 were more feeble, or when they were frequently intercepted by flying clouds. 

 The air however was always not only much better than common air, but better 

 than the air in general produced by the fresh leaves of plants exposed in water to 

 the sun's rays in the experiments of Dr. Ingenhousz ; and under the most favoura- 

 ble circumstances it was so good, that 1 measure of it required 4 measures of 

 nitrous air to saturate it, and 3.65 measures of the two airs were destroyed ; or, 

 proved with nitrous air, it gave la -|- 4ra = 1.35, which, I believe, is better than 

 any air that has yet been produced in the experiments with vegetables. 



The method here adopted of using algebraic characters in noting the result 

 of the experiments made to determine the goodness of air, though not strictly 

 mathematical, is very convenient ; and for that reason, I shall continue to make 

 use of it. a represents the air which is proved : n nitrous air ; and the numbers 

 joined to these letters show the quantities, or the number of measures, of the 

 different airs made use of in the experiment. The other number, which stands 

 alone, or without any letter attached to it, on the other side of the equation, 

 shows the volume, or the number of measures and parts of a measure to which 

 the two airs are reduced after they are mixed. I shall sometimes add a 4th 

 number, showing the quantity of the two airs destroyed, as this more immedi- 

 ately shows the goodness of the air which is proved. Thus, in the experiment 

 last-mentioned, 1 measure of the air proved, mixed with 4 measures of nitrous 

 air, were reduced to 1.35 measure, consequently 3.65 measures of the two airs 

 were destroyed ; for it is ]+ 4 = 5 — 1.35 = 3.65, and the result of this trial 

 I should write thus, la -|- 4w = 1.35, or 3.65. 



Or, for still greater convenience in practice, as this last number 3.65, or 

 3_6^g5_j shows more immediately the goodness of the air in question, by sup- 

 posing with Dr. Ingenhousz, the measure of the eudiometer to be divided into 

 100 equal parts, it will be 100 a -f- AOOn =135, and 365, expressing the volume of 

 the two airs destroyed, will become a whole number. But instead of writing 100 

 a ■\- 400 ra = 135, &c., I shall continue to write la -j- 472 = 135, and shall 

 express the last number (3.65) as a whole number notwithstanding; and I shall 

 sometimes (following the example of Dr. Ingenhousz) write this number only, 

 in noting the goodness of any air in question. 



I would just observe, with respect to the process of proving the goodness of 

 any kind of air, by the test of nitrous air, that I mix the two airs in a phial, 

 about 1 inch in diameter and 4 inches long, putting the air to be proved into 

 the phial first, and then introducing the nitrous air, one measure after another, 

 till the volume of the 1 airs after the diminution has taken place, amounts to 

 more than 1 measure, and is less than 2 measures. Immediately after the intro- 

 duction of each measure of nitrous air, I give the phial a couple of shakes ; 



