\ 



I 



9 



8 



LIGHT, HEAT 



Sect. XIII. i. :> 



the form of gas in the funflilne; but not in the ni^h 



carbon is perfpired along with it. 



(1 



3. A third circumftance, in which the effeas of hght differ ( 

 tially from thofe of heat, appears in the blanching or etiolation of ve- 

 getables ; under whatever temperature of heat a plant is kept, it be- 

 comes white, if the light be excluded from it, and is (o far difeafed, 

 as mentioned iu Sed. XIV. 2. 4. Whence all vegetables turn towards 

 the window, if confined in a room, and in denfe woods grow taller, 

 than in open grounds, for the purpofe of acquiring accefs to this ne- 



cefTary fluid 



O 



th 



IS 



fubje6t 



ny 



periments are related by M 



Senebier on vegetables confined in a dark 



From the experiment lall: related of the nitrous acid becoming 

 loured, when the fuperabundant oxygen was volatilized by the fu 



to 



ht, or attrafted from it ; and from the experiments of bleaching 



by the hyper-oxygenated 



m 



acid.Hvh 



th 



union 



f 



oxygen with the colouring matter feems to deftroy the latter by 

 forming a new acid, which is colourlefs, it appears, that the abfence 

 of oxygen occafions the colour of vegetable bodies, probably by the 



mulation of hyd 



Q 



d that on this account, when they 



•fecluded from the light, they become white, or blanched 



d, by their not bein 



a fituation to part with fo much oxy 



white, and become 



to 



as when they are expofed to the light 

 Hence plants growing in the fhade 

 by being expofed to the fun*s light; for their natural colour beino- 

 blue, the addition of hydrogen adds yellow to this blue, and tans them 

 green. 



I fuppofe a fimilar circumftance takes place in animal bodies ; their 



perfpirable matter is probably hyper- oxygenated 



d 



the funfh 



lofes its fuperabundant oxy 



& 



gen being retained the Ikin becomes tanned yellow 

 mufi: occur in 



as it efcap 

 and by the hydn 



Though 



th 



lefs quantity in animals, as they perfpire fo much lefs 



th 



V 



