5i6 Nitftui Oxlde.'^ColliJiotiJ in vacua. 



fulphur, iron, phofpliorus, and Tiydrogcnc in it, on its decompofition by the compound 

 combuftible bodies, &c. 



3. On its abforbtion in refpiration, with a general inveftigation of this procefs, and the 

 changes effefted in different gafes by it, 



4. A hiftory of its efFedtsi containing the experience of different individuals who have 

 refpired it, furnifhed by themfelves. Every day we gain new evidences in favor of its 

 powers. A number of perfons have breathed it fince the publication of Dr. Beddoes's 

 Notice ■, all have been affefted, and by far the greater number pleafantly. As yet we 

 have tried it in no dtfeafe, except palfy ; but as it fupplies to the fyflem two principles fo 

 effential to perceptive exiflence, as oxygene and nitrogene, and increafes the powers of 

 life generally without producing any afcertainable exhauftion ; there is reafon to hope that 

 it will be a powerful agent in many difeafes of debility. 



An experiment on the collifion of flint and fteel in vacuo, and in carbonic acid, pub- 

 lifhed in my Effay on Heat and Light*, differs confiderably in its refults from a fimilar 

 one made long ago by the ingenious Mr. Hawkfbeef. In repeating my experiment a 

 number of times under new circumftances, I have difcovered the caufe of this difference ; 

 when the gunlock is fnapped in carbonic acid, or in water, if a (harp and thin flint be 

 made ufe of, and the fprings be flrong, a faint red light is generally perceptible : but if 

 the flint be thick, and fufficiently fliarp only to (Irike off particles from the fteel, without 

 fuffering confiderable abrafion of its own parts ; though vivid fparks are produced in the 

 atmofphere, not the flighteft luminous appearance is perceptible in carbonic acid. If in- 

 ftead of flint, fluor fpar, phofphate of lime, or fugar, be rubbed prettly brifkly againft 

 fteel in carbonic acid, as much light is produced as when they are rubbed againft it in 

 common air. Thefe fa£ts induce me to believe, that whenever light is produced by the 

 collifion of flint and fteel in carbonic acid, it arifes from the collifion of fmall particles of 

 flint againft each other, and never from the ignition of fteel. I have often examined in a 

 microfcope, the fmall particles of fteel ftruck off by flint in carbonic acid; the edges are 

 generally deprived of metallic luftre, and exhibit an appearance of fufion; it is probable, 

 however, that this appearance is owing to a partial oxidation of the particle, from the 

 decompofition of the water held in folution by carbonic acid. In Mr. Hawkfbee's expe- 

 riments, the apparatus was contrived in fuch a way, as to produce perpetual abrafion of 

 particles of flint. In my experiment the flint was not fufficiently thin to produce light in 

 carbonic acid, confequently it ought to have produced none in vacuo ; but if (as the 

 fa£ls I am about to detail render probable) the light produced by flint, fluor fpar, phof- 

 phate of lime, &c. on collifion be eledrical, there are ftrong reafons for believing, that 

 in a Torricellian vacuum, or in a vacuum formed by the abforbtion of carbonic acid, by a 

 folution of pot-afli fufficiently concentrated to form a folid compound with it, no light 

 would be vifible. 



* Weft Country Contributions, t Pl>il. Tranf. No. XXIV. 1185. (01 Hawkfbee's Phyfico- 



mechan. Exper. id edit, oftavo, London, 1719, page i<>.) , 



- . 4. Mr." 



