on various Oljects, 405 



upon the -^^ of hydrogen pre-existing in the lube and 

 adaptors, the loss ojf' hydrogen will be found proportionally 

 rather greater than that of nitrogen. 



In another experiment in which three grains of potassium 

 were employed in the same manner, 6*78 cubical inches of 

 ammonia were found to be absorbed, and 2*48 of hydrogen 

 only iienerited. The distillation was performed, the adantors 

 and tube heing full of common air: 8 cubical inches of 

 gas were pr«;;aced; and there must haife remained in the 

 lubes and adaptors, the same quantity of residual air as in 

 the process last described. 



The 8 cubical inches of gas contained scarcely -S- of a 

 cubical inch gf ammonia; and the unabsorbable part de- 

 tonated with (^xvgcn, in the proportion of 1 1 to 6, gave a 

 residuum of 7'5. — The barometer was at 30*2'"', thermo- 

 meter at 52^ Fahrenheit. Dr. Pearson, Mr, Allen, and 

 Mr. Pepys were present during thq whole of these opera- 

 tions, and kindly assisted in the progress of them. 



Now 6*78 — '4 of ammonia = 6*38, and this quahtity of 

 gas decomposed by electricity, would afford 11*4 of per- 

 manent gas, consisting of 2*9 nitrogen, and 8*5 hydrogen; 

 but there are produced in this experiment,, of hydrogen, 

 2*48 in the first operation, and 4*28 in the second, and 

 considering the nitrogen in the permanent gas as 3*32, '8 

 must be subtracted for the common air; which would 

 give 2*52 for the nitrogen generated; and to these must be 

 added, the quantity of hydrogen and nitrogen in the tubes 

 and adaptors. 



The quantity of potassium regenerated was sufficient to 

 produce 2*9 cubical inches of hydrogen. 



In all experiments of this kind, a considerable quantity 

 of black matter separated, during the time the potassium 

 in the tube was made to act upon water. 



This substance was examined. It was in the state of a 

 fine powder. It had the lustre of plumbago, it was a con- 

 ductor of electricity. When it was heated, it took fire at 

 a temperature below ignition ; and after combustion, no- 

 thing remained but minutely divided platiiia. 



I exposed some of it to heat in a retort containing oxy- 

 gen gas ; there was a diminution of the gas; and a small, 

 quantity of moisture condensed on the upper part of the 

 retort, which proved to be mere water. 



I made two or three experiments, with a view to ascer- 

 tain the quantity of this substance formed, and to deter- 

 mine more fully its nature. I found that in the process in 

 which from three to four grains of potassium were made 



C c 3 to 



