204 PHILOSOPHICAL TRANSACTIONS. [aNNO 1787. 



tity of air, which appeared to be better than that furnished by any of the 5 

 other globes. Proved with nitrous air, it turned out la -|- 3n = I.07, or 293 ; 

 and, what was particular, the water did not appear to have altered its colour in 

 the least, or to have lost any thing of its transparency. 



Exper. 10. The globe, N° 5, with ravelings of linen, was very tardy in 

 furnishing air, and produced but a small quantity ; at the end of a fortnight, 

 however, I collected about 2 cubic inches, which, proved with nitrous air, gave 

 \a-\- 671— 1.51, or 249. 



Exper. 1 1 . The globe N° 6, with human hair, furnished still less air than 

 with ravelings of linen in the last mentioned experiment ; but, notwith- 

 standing the smallness of the quantity, it was considerably superior in quality to 

 atmospheric air; for, proved with nitrous air, it gave la -f- 27i = 1.45, or 155 ; 

 whereas common air, proved at the time, gave la -j- Iw = 1.08, or 92. 



Exper. 12. To ascertain the relative goodness of the air furnished by the 

 water in these experiments, and of that produced by exposing fresh healthy 

 vegetables in water to the action of the sun's light, according to the method of 

 Dr. Ingenhousz, I collected a small quantity of air from a stem of a pea plant, 

 which had 4 healthy leaves on it, and found it to be much inferior to that fur- 

 nished in the experiments with silk, and the various other substances I made use 

 of. Proved with nitrous air, it gave la-|-272= 1.05, or 195. And similarly 

 with other plants. 



With a view of determining, with greater precision, the quantity and the 

 quality of the air produced by a given quantity of water and silk, exposed for a 

 given time to the action of the sun's rays, I made the following experiment. 



Exper. 13. A globe of fine, clear, white glass, about 8^v inches in diameter, 

 and containing 296 cubic inches, being filled with fresh spring water, and 30 

 grains of raw silk, was exposed in my window three days, being for the most 

 part cold and cloudy, with short intervals of sunshine. Air produced 9.1 cubic 

 inches; quality la -f 3n.= I.61, or 239. 



Similar experiments being repeated on several successive days, the quantities 

 and qualities of the airs furnished on the different days were as follow : 



Quantity. Quality. 



On the 12th, 13th, and 14th of May 9\ cubic inches la + Sn = I.61, or 239 



15th 8/^ Ic + +w = 1.74-, or 32^ 



16th 9 la + 4« = 1.44, or 356 



17th 6 la + 4«= 1.35, or 365 



18th I la + 4n = 1.56, or 344 



19th I la -j- 4« =. 1.74, or 32() , 



Total quantity 33^*6 Mean quality la + 4m = 1.84, or 3l6' 



As in this experiment the air furnished each day was removed at night, and 



