as ■Oijeffs of the Art ofDytng^ iSc. 369 



quantity of light they receive, and which, joining 

 with it, gives it elafticity. But plants, kept in 

 the dark, throw out none of this air, and are white. 

 Thofe of the fame kind, expofed to a weak light, 

 will have fome of the air feparated, and have 

 a faintdegree of colour; and thofe, which undergo 

 the aftion of a ftrong light, will exhibit vivid 

 tints. But though we allow of the dephlogifti- 

 cated air as producing whitenefs, yet we may alfo 

 acknowledge the effeft of phlogifton in pro- 

 ducing colour; and, in fad, the antiphlogiftians 

 are obliged to admit of inflammable gas as a 

 fubftitute for it; and, to acknowledge, that this 

 gas, which they fuppofe to be the other confti- 

 ttjent part of wat^r, is the principle of colour*. 



The colourlefs ingredients ufed in dying 

 confift of alkaline, acid, nitrous, earthy, and 

 metallic, falts, which contribute either to extrad 

 the colouring matter, from other fubflrances 

 which contain it; or, by either attenuating or 

 incraflating its particles, to caufe the colour to 

 afcend or defcend, according to the prifmatic 

 range. Tirus, acids raife the blue colour of ve- 

 getable juices to indigo, violet, red, and yellow, 

 while alkalis reduce the tints, thus raifed, to 

 violet, indigo, blue, and, on a farther addition, 

 to green. 



• Journal de Phyfjque^ tome XXVI. part I. 

 Vor,. III. B b In 



