128 Itev.W. V. Harcourt on Lord Brougham's statements 



and the other liable, in part, to lose its elasticity*; he ex- 

 tended his experiments on the generation of " factitious 

 airs" to a variety of materials, multiplying them to such an 

 extent that one of Cotes's hydrostatical lectures is filled with 

 the repetition of them; he remarked the condensability of 

 muriatic acid gast, and the orange colour of nitrous acid gas \\ 

 and extricated from red lead, by the burning-glass, the gas§, 

 which Priestley afterwards ha\ ing obtained by the same method, 

 was led by reasoning from the manner in which red lead is 



* " Experiment 8. — A mercurial gauge having been put into a conical 

 glass whose bottom was covered with beaten coral, some spirit of vinegar 

 was poured in, and then the glass stopper closing the neck exactly : on the 

 working of the menstruum on the coral, store of bubbles were for a good 

 while produced, which successively broke in the cavity of the vessel ; and 

 their accession compressed the confined air in the closed leg of the gauge 

 three divisions, which I guessed to amount to about the third part of the 

 extent it had before; but some hours after the compression made by this 

 newly-generated air grew manifestly fainter, and the imprisoned gauge-air 

 drove down the mercury again, till it was depressed within one division of 

 its first station ; so that in this operation there seemed to have been a 

 double compressive power exercised, the one transient by the brisk agita- 

 tion of vapours, the other durable from the aerial or springy particles either 

 produced or extricated by the action of the spirit of vinegar on the coral." 

 — Phil. Trans. 1675. 



f " May 26, 1676. — Sal-ammoniac was put into a receiver with a suffi- 

 cient quantity of oil of vitriol. Then the air being exhausted, the salt was 

 put into the oil, whereupon a great ebullition presently followed, and the 

 mercury in the gauge showed a good quantity of air to be generated; but 

 this by the same gauge soon after appeared to be destroyed again. The expe- 

 riment was repeated, and both the production and destruction were slower 

 than before. It was confirmed by these trials that some artificial airs may 

 be destroyed, but why this destruction happens sometimes sooner and 

 sometimes slower, may perhaps seem worthy of further inquiry." — 2ndcont. 

 Phys. Mech. Expts. 1676. 



+ « We put an ounce of such strong spirit of nitre as is above mentioned 

 into a moderately large bolt head, furnished with a proportionable stem, 

 over the orifice of which we strongly tied the neck of a thin bladder, out 

 of which most part of the air had been expressed, and into which we had 

 conveyed a small phial with a little highly rectified spirit of wine. Then 

 this phial, that was before closed with a cork, being unstopped without 

 taking off the bladder, a small quantity, by guess not a spoonful, of the al- 

 cohol of wine was made to run down into the spirit of nitre, where it pre- 

 sently produced a great commotion, and blew up the bladder as far as it 

 would well stretch, filling also the stem and cavity of the glass with very 

 red fumes, which presently after forced their way into the open air, in 

 which they continued for a good while to ascend in the form of an orange- 

 coloured smoke." — New Experiments about Explosions, 1672. 



§ f September 4, 1678. — 1 exposed one ounce of minium in an open 

 glass to the sunbeams, concentrated by a burning-glass, and found that it 

 had lost three-fourths of a grain of its weight, though much of the minium 

 had not been touched by the solar rays. May 29. — Repeated the same 

 experiment, in a light glass phial sealed hermetically and exactly weighed, 



