498 PHILOSOPHICAL TRANSACTIONS. [ANNO 1784. 



comes over, and at the same time part of the quicksilver rises in its metallic 

 form, and also part of the white mass, united in all probability to a greater pro- 

 portion of acid than before, sublimes ; so that the rationale of the production of 

 dephlogisticated air from turbith mineral, and from red precipitate, are nearly 

 similar. 



True turbith mineral consists of the above-mentioned white mass, well washed 

 with water, by which means it acquires a yellow colour, and contains much less 

 acid than the unwashed mass. Accordingly it seems likely, that on exposing 

 this to heat, less of it should sublime without being decompounded, and conse- 

 quently that more dephlogisticated air should be procured from it than from the 

 unwashed mass. This is an instance, that the superabundant vitriolic acid may, 

 in some cases, be better extracted from the base it is united to by water than by 

 heat. Vitriolated tartar is another instance ; for, if vitriolated tartar be mixed 

 with oil of vitriol and exposed even to a pretty strong red heat, the mass will be 

 very acid ; but if this mass be dissolved in water, and evaporated, the crystals 

 will be not sensibly so. 



In all probability, the vitriolic acid acts in the same manner in the production 

 of dephlogisticated air from alum, as the nitrous does in its production from 

 nitre; that is, the watery part comes over first in the form of dephlogisticated 

 air, leaving the acid charged with its phlogiston. Whether this is also the case 

 with regard to green and blue vitriol, or whether in them the acid does not 

 rather act in the same manner as in turbith mineral, I cannot pretend to say, 

 but I think the latter more likely. There is another way by which dephlogisti- 

 cated air has been found to be produced in great quantities, namely, the growth 

 of vegetables exposed to the sun or day-light ; the rationale of which probably 

 is, that plants, when assisted by the light, deprive part of the water sucked up 

 by their roots of its phlogiston, and turn it into dephlogisticated air, while the 

 phlogiston unites to, and forms part of, the substance of the plant. 



There are many circumstances which show, that light has a remarkable power 

 in enabling one body to absorb phlogiston from another. Mr. Senebier has ob- 

 served, that the green tincture procured from the leaves of vegetables by spirit 

 of wine quickly loses its colour when exposed to the sun in a bottle not more 

 than -l part full, but does not do so in the dark, or if the bottle is quite full of 

 the tincture, or if the air in it is phlogisticated ; whence it is natural to conclude, 

 that the light enables the dephlogisticated part of the air to absorb phlogiston 

 from the tincture; and this appears to be really the case, as I find that the air in 

 the bottle is thus considerably phlogisticated. Dephlogisticated spirit of nitre 

 also acquires a yellow colour, and becomes phlogisticated, by exposure to the 

 sun's rays;* and I find on trial that the air in the bottle in which it is contained 



* If spirit of nitre is distilled with a very gentle heat, the part which comes over is high coloured 

 and fuming, and that which remains behind is quite colourless, and fumes much less than other ni- 



